This PDF file contains the front matter associated with SPIE Proceedings Volume 10706, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Concepts for the largest future space observatories have reached the limit of the most capable launch vehicles likely to be available over the next two decades. Moreover, unless there is a paradigm change in how future “flagships” are designed, developed, and deployed, it will be a major challenge to afford them. At the same time, significant advances are taking place in the coming decades that have the potential to enable high-priority major space observatories, including (1) significant cost reduction in medium-lift vehicles; (2) continuing advances in capabilities for robotic/telerobotic servicing and assembly; (3) deployment in cis-lunar space of a human habitation and operations facility; and (4) advances in the capabilities of scientific instruments. Taken together, these developments offer in the relative near term opportunities for creative designs for future major observatories to allow sophisticated on-orbit upgrade, as well as eventual space assembly. This talk will summarize work to date on servicing and space assembly, including HST, ISS, and robotic programs, as well as near-future developments that may be the only path to the most ambitious space observatories. Finally, although at present relatively little work has been undertaken on the topic, I will note some ways in which space servicing and assembly might enable lower-cost “flagship” missions.

Over its more than thirty-year history, the Advanced Technologies and Instrumentation (ATI) program has provided grants to support technology development for ground-based astronomy. Research from this program has advanced adaptive optics, high resolution and multi-object spectroscopy, optical interferometry and synoptic surveys, to name just a few. Previous and ongoing scientific advances span the entire field of astronomy, from studies of the Sun to the distant universe. Through a combination of literature assessment and individual case studies, we present a survey of ATI funded research for optical-infrared astronomy. We find that technology development unfolds over a time period that is longer than an individual grant. A longitudinal perspective shows that substantial scientific gains have resulted from investments in technology.

This contribution is focused on the innovative aspects of the design of the Laser Guide Star (LGS) Facility for the Gran Telescopio Canarias (GTC) Adaptive Optics (GTCAO) System [6]. After a trade-off process considering different alternatives, a preliminary opto-mechanical design was defined, based on a “TOPTICA SodiumStar” laser to be launched on-axis. To maximize throughput, different novelties around the optical, and mechanical design of the Laser Launch System, including the Laser Head, the Beam Transfer Optics and the Launch Telescope are emphasized in this paper. In particular, all the elements of the Laser Launch System have been compacted to be placed at the backside envelope of the GTC M2 mechatronics. To fit in that envelope the thermal enclosure of the Laser Head had to be redefined to avoid mechanical interferences and science beam vignetting. An innovative closed-loop Laser Head cooling approach was defined to be also arranged at the backside of GTC M2. Performance simulations running in parallel to the on-axis LGS design could not determine any difference in performance between the on-axis and the off-axis launch. Hence, considering the higher packaging and maintenance complexity required by the on-axis launch, GTC decided to define the off-axis configuration as the new baseline approach. All the solutions already defined for the on-axis approach that were applicable to the new off-axis baseline were reused. To reduce the cost of future upgrades, the LGS design allows generating and launching several LGS with just one launch telescope splitting the light from the Laser Head. In parallel with keeping the volume of the facility to a minimum, an effort to keep its maintenance as simple as possible has been also made to avoid the impact on the telescope operational costs.

The power of the next generation of telescopes that will rely largely on the combination of light-collecting area with excellent (ideally: diffraction limited) image quality. Therefore, the focus will heavily lean on adaptive optics and the near infrared wavelength regime. A severe limiting factor is the presence and strength of atmospheric OH emission lines in the NIR. OH suppression techniques involving fiber Bragg gratings (FBG) have been proposed, however as yet not fully demonstrated on sky. We are involved in the first generation FBG prototype development with partners in Australia, including the GNOSIS and PRAXIS on-sky experiments. Since the supply of suitable multi-notch filters is no longer available from industry, we have made an effort at innoFSPEC Potsdam to build a specialized laboratory for the development and manufacture of 2nd generation FBGs for OH suppression. Suppression of the strong NIR OH emission lines requires a single grating that reflects multiple wavelengths, spaced at non-periodic intervals, with flat-top profile and high suppression ratio. It has been shown that aperiodic fiber Bragg gratings (AFBGs) can provide such functions. However, the fabrication technology requires accurate optical alignment of several degrees of freedom as well as complex control of modulated beams to form a varying interference pattern. In our work, an algorithm is developed from the index profile of a multi-notch AFBG to the design of a complex phase-mask that can generate a matching UV diffraction pattern, which will in turn inscribe an single-mode fiber into the chosen AFBG. With such a phase mask, the fabrication of the AFBGs will be reduced to a simple UV-exposure process, i.e., the complex alignment and control processes of the interference pattern from modulated beams are avoided altogether. The resulting reliable and reproducible fabrication process will dramatically reduce of the cost of such filters. Packaging aspects for a complete sky emission filter system will also be discussed.

WEAVE is a new wide-field multi-object spectroscopy (MOS) facility proposed for the prime focus of the 4.2m William Herschel Telescope (WHT), situated on the island of La Palma, Canary Islands, Spain. To allow for the compensation of the effects of temperature-induced and gravity-induced image degradation, the WEAVE prime focus assembly will be translated along the telescope optical axis. The assembly comprises the prime focus corrector (PFC), a central mount for the corrector known as FTS^[1], an instrument rotator and a twin-focal-plane fibre positioner. SENER, that manufactured and delivered the FTS, is also responsible for the final design, manufacturing, integration, alignment and testing of the PFC and its ancillary equipment. This manuscript describes the final design of the PFC along with the analyses and simulations performed and presents the procedures for the integration and alignment of the lenses in the corrector.

The Fast-Steering Secondary Mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1m diameter segments with effective diameter of 3.2m. Each segment is held by three axial supports and a central lateral support with a vacuum system for pressure compensation. Both on-axis and off-axis mirror segments are optimized under various design considerations. Each FSM segment contains a tip-tilt capability for guiding to attenuate telescope wind shake and mount control jitter. The design of the FSM mirror and support system configuration was optimized using finite element analyses and optical performance analyses. The design of the mirror cell assembly will be performed including sub-assembly parts consisting of axial supports, lateral support, breakaway mechanism, seismic restraints, and pressure seal. . In this paper, the mechanical results and optical performance results are addressed for the optimized FSM mirror and mirror cell assembly, the design considerations are addressed, and performance prediction results are discussed in detail with respect to the specifications

With more rapid, affordable access to space and the emerging availability of large-volume fairings, owners and users of current and future space-based optical systems are desiring large-aperture or segmented-aperture primary mirrors for their missions. This demand is driving the need for new approaches to optical component fabrication to produce mirrors and mirror segments that are more cost-efficient with faster manufacturing lead times than traditional optical components. Harris Corporation is executing a mirror development strategy called Advanced Mirror Construction (AMC) to meet this need while still meeting the challenging requirements of space-based optics. A key component of this strategy is the utilization of replication to produce precision lightweight mirror components. We present the motivation and initial results for lightweight replicated, ultra-stable mirrors and mirror segments as well as other key elements of the AMC strategy.

The NASA Strategic Astrophysics Technology (SAT) Program was established in 2009 as a new technology maturation program to fill the gap in the Technology Readiness Level (TRL) range from 3 to 6. Since the inception of the program, 47 tasks have been awarded under the auspices of the NASA Physics of the Cosmos (PCOS) Program in the areas of optics and detectors as well as lasers, electronics, and micro-thruster subsystems. In addition, 31 tasks have been awarded under the auspices of the NASA Cosmic Origins (COR) Program to develop optics, coatings, cooling subsystems, and detectors from the Far-IR to the Far-UV. We present the PCOS/COR portfolio distribution in terms of specific technology areas addressed and show an analysis of the rate and cost of TRL advancements. We present highlights of the infusion success stories that have emerged from the SAT maturation program as it relates to enabling future NASA astrophysics strategic missions. Finally, we present an outlook for future technology priorities for investment by the SAT Program.

Segmented mirror technology is essential for large telescopes. Actually, the world largest telescopes such as Keck I and II, and GTC employ segmented mirrors for the primary mirrors, and all the planning extremely large telescopes (TMT, E-ELT, and GMT) also plan to use the segmented mirrors although the size of one mirror is far from each other. Needless to say, the technology of segmented mirrors realizes not only telescopes with the large apertures, which cannot be fabricated with a single dish, but also lightens the total weight of the telescopes. In addition, it enables the manufacture of the mirrors with a relatively small equipment and can simplify the mechanical structure of the telescope, resulting in saving the total cost for development. However, there are native difficulties and issues for the segmented mirrors technology. First, the segmented mirrors must be aligned to each other in the positions and angles with an accuracy of several tens of nanometers and arcsec, and it must be stabile for a long time by the active control as for TMT, the very complicated technique and the human resources are needed for precise control of as many as 492 mirrors. Secondly, individual polishing process of segmented mirrors produces, unavoidable sagging at the outer circumference of the mirrors. Because these local surface deformation cannot be compensated by the alignment of mirrors, the PSF by the telescope is strongly affected by the remaining wave front error, which is the higher order. Finally, the ambient thermal radiation leaked t from the gaps between segment mirrors , which becomes a background noise source, significantly degrades the sensitivity of the instrument, especially near-IR or mid-IR instruments, compared with a single dish telescope. These problems arises from the fact that each segmented mirrors are independently supported with the gaps. Therefore, we have been developing Alignment-Free Gapless Segmented Mirror (AFGSM), which is mechanically fixed to each other without any gaps between mirrors, as if it were a monolithic type of mirror. Specifically, after fan-shaped or similar segment mirrors are manufactured individually, they are mechanically fixed to each other by fastening, fusing or bonding. Since the Orthogonality or parallelism of the mirror surface from its reference surface is finished with a machine precision of 1 um or less, the assembly can be mechanically carried out with a well accuracy. Polishing to obtain a highly precise surface for use as a telescope, can be to the extent of corrected (re-)polishing. ^ In order to realize such a segmented mirror, we selected ceramics cordierite CO720 as a material, which is a type of fine ceramic developed by Kyocera. The cordierite CO720 has a coefficient of thermal expansion (CTE): <0±0.02ppmK - 1 for 23 deg., which is comparable to that of low thermal expansion glass such as Clearceram, Zerodur, or ULE. Since it can be easily polished, it is suitable for the base material of a mirror for a telescope application. Indeed, as a material comparable to low thermal expansion glass such as Zerodur, cordierite CO720 is widely used in cutting-edge technology of semiconductor manufacturing equipment which requires extremely high accuracy. Cordierite has a stiffness (E / ρ) of about 1.5 times that of general low thermal expansion glass material. With AFGSM, it is necessary to fasten / bond / join segments to each other. Cordierite CO720 is more suitable for gapless mirrors because the mirror surface is less likely to be deformed compared to glass against the stress generated during assembly, thanks to its high stiffness characteristics. Also, the high flexibility of formability of cordierite is also important in order to realize a gapless segmented mirror. In order to minimize the alignment error, the two contacting surfaces must ideally be processed as perpendicularity angles to the mirror reference. In addition, if there is a gap on the contacting surface, deformation will occur due to the tightening force at the time of fastening, so flatness also becomes important. Further, its high flexibility of formability of cordierite is an advantage also for providing a honeycomb structure for weight reduction. In ordinary glass materials, a honeycomb structure is realized by grinding from the bulk state, so that much processing time is required. On the other hand, in the case of cordierite ceramics, machining can be carried out at the stage of a soft molded body such as chalk after raw material forming and before firing. Therefore, costly grinding can be performed quickly and easily, which contribute overall cost reduction. Finally, the long term dimensional stability of cordierite is also suitable for general telescope mirrors. Low thermal expansion glass is cooled for a very long time in order to release the internal stress in the material during molding process. Therefore, the molded material takes a long time to deform. For example, in the case of Zerodur, deformation value 129 nm/m/1 year is expected as according to our research with PTB. In case of cordierite, deformation after firing is extremely small (< 3.8nm/ m/ year) compared to the low thermal expansion glass and it is possible to maintain stable dimensions over a long period of time. In order to demonstrate the feasibility of Gapless mirrors, in this study we made a prototype of Dia.300mm parabolic mirror sample. As a result of the structural analysis for fixing the mirrors, the shape of the segmented mirror was a fan shape with an internal angle of 60 degrees and it was divided into six parts. Triangle parts (three parts) was one of the concepts for this trial, but distortion at mirror surface coming from assembling each individual mirrors tend to be created easily, and therefore, we rejected this three parts option. Regarding the honeycomb structure, there are many cases where honeycomb designs of the same shape are used over the entire surface such as triangle and hexagon in the case of a monolithic mirror. Segmented mirror used for this evaluation, however, has a relatively small diameter of 300 mm, and it was confirmed by simulation that sufficient rigidity of cordierite material can be obtained without providing a complicated honeycomb structure. For this reason, we prioritize the workability for bolting in the horizontal direction on the contacting surface of the mirror, and an assembling structure was selected that can easily perform the assembly process. In addition, the thickness of the rib is made thicker than the other parts so that the contacting surface does not deform even by tightening with a bolt. It is confirmed that this structure does not lose practicality even if the mirror up to 1 m in diameter is scaled up. Individual segmented mirrors are manufactured independently from forming, green machining, firing and grinding, which is a standard ceramic manufacturing process, and then six segment mirrors are fastened with bolts with precision. After aligning the height of all mirror surfaces by grinding process, the polishing process is performed at the end in order to remove any height gap at the mirror surface. As a result, it was confirmed that sagging hardly occurred at the joint area, and ideal mirror surface condition was achieved measured by interferometer. Furthermore, in order to quantitatively investigate the occurrence of deviation of each segment after assembly, a flat surface sample was also prepared. After checking the surface accuracy using the laser interferometer for the polished flat mirror, we confirmed that there was no significant segment mirror misalignment by thermal cycle test and vibration test. In this presentation, in addition to the design results of the prototype AFGSM, the optical performance of the parabolic mirror obtained as a result of the polishing process, and the results of the environmental test are reported. We also discuss applicability of ceramic segment mirrors for space telescopes and some other observation devices.

Optimization techniques are powerful tools for producing lightweight structures with the maximum structural stiffness. They allow an optimized design to be produced directly for a given structure and, in this way, save considerable time in the design phase of a structure by avoiding multiple iterations between the definition of the design under computer-aided design (CAD) and the verification of the performance under finite-element (FE) analysis. There are three classes of optimization: size optimization, shape optimization and topology optimization. The topology optimization technique aims to find an optimal distribution of material given boundary conditions, i.e. the fixing points and the external loads. It starts from an initial volume representing a blank of the structure and removes the most unused material to meet the objective of mass reduction. In optomechanical engineering, this technique is met in the design of lightweight mirrors and especially in the design of their core-cell shapes. To provide reliable and useable results, this technique requires a fine and regular mesh of the mirror as well as a postprocessing of the results by the mechanical engineers. These constraints, combined with the necessity of using 3-D models, contribute an increase in the computation time and complicate the meshing. We propose here an innovative approach to this design problem by using topography optimization instead of topology optimization. Topography optimization, also named bead optimization, is a branch of the shape optimization and consists in introducing beads to a surface in order to increase its structural stiffness. The main advantage of this technique is that shell models can be used instead of solid models, easing the meshing operation and decreasing the number of degrees of freedom in the FE model, and thereby reducing computation cost. This paper presents an example of the application of this technique to the design of the primary mirror panel of the GCT (Gamma-ray Cherenkov Telescope), a dual-mirror 4-meter telescope proposed for the future Cherenkov Telescope Array. FE models and optimizations are made with MD.Patran and MD.Nastran respectively.

Large optic fabrication is a delicate and time consuming process. Obtaining a large prime optic is often in the critical path of a project and poses a serious risk to both the schedule and budget. The Optical Engineering and Fabrication Facility (OEFF) at the College of Optical Sciences, the University of Arizona, has developed a new way of optimizing its large optic fabrication process for maximum efficiency in convergence. The new process optimization takes the amount of stock material removal, tool characteristics, metrology uncertainty, optic prescription, optic material properties, and resource availability as input parameters and provides an optimized process along with an achievable convergence. This paper presents technical details of the new process optimization and demonstrates performance on 6.5m mirror fabrication at the University of Arizona. Two case studies for an 8.4m GMT off-axis primary mirror segment and a 3.1m TMT convex secondary mirror fabrication are also presented.

A manufacturing technology of mirrors for free-space optical communication is presented: a thin layer of Nickel is deposited on a master and bonded on a light-weighted structure by adhesive. After separation, the master is ready for another cycle. The process is cost-effective because only the master needs to be of optical quality. The structure is machined by traditional tooling, with figure errors compensated by the adhesive. Its curing time defines the process throughput to one mirror per day per master. Several 200 mm-aperture Ritchey-Chrétien telescopes have been manufactured and tested.

We present two methods for generating novel hyper-crossing tool paths for use with CNC and robotic sub-aperture polishing techniques. One generation method utilizes an optimization based on a Voronoi diagram. The second method is seeded by a unicursal pseudo-random pattern to generate a hyper-crossing tool path which features many self-crossings over the entire part surface. Each instance of generation for a given surface for either algorithm will result in a new hyper-crossing pattern. Tool paths can be generated for any surface area including those with interior holes. We also present results of an experiment using a hyper-crossing tool path to remove diamond turning marks.

Systems like TESS require specialized components that challenge all involved. These systems consist of many sub-components, but we are focused on the refractive and reflective optical components. One purpose of this talk is to introduce optical system designers to application specific manufacturing processes. We, as manufacturers, need to tailor our processes for the optic’s specific operational environment. In addition, we want to introduce some of our more unique manufacturing capabilities to allow system designers to widen their design space. It is now feasible to manufacture a wide range of sizes, shapes, and materials for many different applications.

We present a manufacturing process based on the deterministic polishing and figuring of thin glass substrates (shells), with thickness ranging from 0.5 up to a few millimeters, in “stand-alone” configuration or as part of a composite sandwich structure with low-density core. The methods will be well suited for a broad range of applications in astronomy like, e.g., the production of thin substrates for adaptive optics, the realization of sandwiched lightweight segments for the mirrors of future ground-based and space telescopes, and the realization of low-cost mirrors for amateur astronomy telescopes. The method foresees the pre-shaping of thin glass substrates via hot slumping technology followed by highprecision form correction of the optical surfaces via computer-controlled bonnet and ion beam figuring technologies. During the phase of bonnet polishing of a shell in stand-alone configuration, a removable holder stiffens it temporarily. This paper describes the main steps of the process under study and reports on the realization of the first prototypes.

Additive manufacturing (AM), more commonly known as 3D printing, is a commercially established technology for rapid prototyping and fabrication of bespoke intricate parts. To date, research quality mirror prototypes are being trialled using additive manufacturing, where a high quality reflective surface is created in a post-processing step. One advantage of additive manufacturing for mirror fabrication is the ease to lightweight the structure: the design is no longer confined by traditional machining (mill, drill and lathe) and optimised/innovative structures can be used. The end applications of lightweight AM mirrors are broad; the motivation behind this research is low mass mirrors for space-based astronomical or Earth Observation imaging. An example of a potential application could be within nano-satellites, where volume and mass limits are critical. The research presented in this paper highlights the early stage experimental development in AM mirrors and the future innovative designs which could be applied using AM.

The surface roughness on a diamond-turned AM aluminium (AlSi₁₀Mg) mirror is presented which demonstrates the ability to achieve an average roughness of ~3.6nm root mean square (RMS) measured over a 3 x 3 grid. A Fourier transform of the roughness data is shown which deconvolves the roughness into contributions from the diamond-turning tooling and the AM build layers. In addition, two nickel phosphorus (NiP) coated AlSi₁₀Mg AM mirrors are compared in terms of surface form error; one mirror has a generic sandwich lightweight design at 44% the mass of a solid equivalent, prior to coating and the second mirror was lightweighted further using the finite element analysis tool topology optimisation. The surface form error indicates an improvement in peak-to-valley (PV) from 323nm to 204nm and in RMS from 83nm to 31nm for the generic and optimised lightweighting respectively while demonstrating a weight reduction between the samples of 18%. The paper concludes with a discussion of the breadth of AM design that could be applied to mirror lightweighting in the future, in particular, topology optimisation, tessellating polyhedrons and Voronoi cells are presented.

WEAVE is the new wide field multi-object and integral field survey facility for the prime focus of the 4.2 m William Herschel Telescope. It is located at the Observatorio Roque de los Muchachos, in La Palma, Canary Islands, Spain. WEAVE fiber-fed spectrograph offers two resolutions, R ~ 5000 and 20,000. It has a collimator mirror and two cameras optimized for the wavelength intervals of 366 - 959 nm and 579 - 959 nm, respectively. One of the responsibilities of INAOE within the WEAVE collaboration is the polishing of the collimator mirror, made of OHARA CLEARCERAM®- Z HS. The collimator has a diameter of 660 mm, a central thickness of 44.7 mm and a weight of 56.8 kg. The main specifications are: 2 fringes irregularity in a clear aperture of 624 mm diameter and a radius of curvature of 1224.65 mm +/- 0.15. In this work, we present the polishing process and final results for the collimator. In particular, we describe the tools developed for its manufacturing, the modifications carried out to the conventional polishing machine to support the glass. Additionally, the interferometric optical irregularity measurements are presented. The collimator polishing process is finished fulfilling all the optical specifications.

The project "Novel Astronomical Instrumentation based on photonic light Reformating" is a DFG-funded collaboration to exploit the recognized potential of photonics solutions for a radically new approach to astronomical instrumentation for optical/infrared high precision spectroscopy and high angular resolution imaging. We present a project overview and initial development results from our Adaptive Optics-photonic test bed, Ultrafast Laser Inscribed waveguides for interferometric beam combination and 3D printing structures for astronomical instrumentation. The project is expected to lead to important technological breakthroughs facilitating uniquely functionality and technical solutions for the next generation of instrumentation.

COLIBRI is one of the two robotic ground follow-up telescopes for the SVOM (Space Variable Object Monitor) mission dedicated to the study of gamma-ray bursts, allowing determination of precise celestial coordinates of the detected bursts. COLIBRI telescope is a two-mirror Ritchey-Chrétien telescope whose concave primary and convex secondary mirrors have diameters of 1325mm and 485mm respectively. The mirrors are currently manufactured at LAM (Laboratoire d’Astrophysique de Marseille). In this article, the advancement of the work is presented. We also give a global overview and status of the COLIBRI project.

High-precision aspheric components are widely used in modern systems with the capability of high image quality, but an high-slope convex aspheric aspheric surface is more challenging to fabricate because of its more complex shape and measuring difficulty compared with other surfaces. As the traditional aspheric surface manufacturing will cause many problems like the tools cannot conform to the local varying curvatures of high slope convex aspheric optics. In this paper, a high efficient approach include CNC generating, MRF fine polishing and multi-wavelength interferometer measurement to get a high-precision convex aspheric surface is presented. A kind of flexible tools was designed to polish the surface and correct MHSF errors on the aspheric surface which can always conform to the surfaceduring the process. And the pressure needed during the polishing process is simulated by COMSOL software. A high-precision convex aspheric surface is successfully obtained and the final surface RMS is better than λ/30.

Cordierite ceramics offer several interesting advantages over traditional glass materials for ultra-lightweight and thermally-stable space optics. The authors have conducted a research and development activity to establish a technology for manufacturing lightweight cordierite mirrors for next-generation space telescopes.

In this activity, a 0.7-m spherical cordierite mirror was manufactured as a mock-up. The mirror substrate was formed to a lightweight rib structure using a near net shape forming process. The rib pattern was designed assuming a hexagonalshaped mirror segment, and the original outer shape was circular for an easy polishing process before outline machining. The weight was 21.3 kg with the original circular shape, but will be reduced to 12.3 kg (at areal density of 38.5 kg/m²) by processing it into the hexagonal outline. The surface figure accuracy was 154 nm RMS (root mean square). As the outer shape will then be processed to become hexagonal, there was no need to further improve the accuracy.

The prototype of a 0.3-m aspherical cordierite mirror was also manufactured with more difficulty. This mirror was parabolic in shape, assuming the primary mirror of a Cassegrain telescope, and its substrate was further reduced in weight. Thus, a weight of 1.91 kg was achieved (at areal density of 24.6 kg/m²), and the surface figure accuracy reached 35 nm RMS.

As a result of these prototyping efforts, cordierite mirrors are expected to be applied in space optics that require extremely high observation performance, combined with large-size, ultra-lightweight, and high-precision features.

ZERODUR is utilized in many ultra-precision applications such as IC and LCD Lithography, High-end Metrology, Aviation and space born or ground based Astronomy. Glass ceramics exhibit an extremely low coefficient of thermal expansion (CTE) together with an excellent homogeneity of CTE. Currently, the material demand of those ZERODUR applications is continuously growing. In parallel, CNC machined parts are getting more and more complex and require more advanced machining capabilities. This paper reports on the actions SCHOTT is taking to fulfill the increasing demand on high precision material and components. SCHOTT increased capacity along the entire value stream of ZERODUR production, starting from melting up through CNC machining. New CNC machines, together with process improvements, establish a new set of capabilities for up to four-meter-class substrates. Results are reported, demonstrating tighter tolerance on mirror surface figure together with reduced sub surface damage for accelerated polishing. The new equipment will enable SCHOTT to lightweight 4 m class mirror substrates for future space optics as well as serial production of smaller segments for larger diameter telescopes.

Most materials naturally expand when heated and contract when cooled; this is known as thermal expansion and is typically characterized by a Coefficient of Thermal Expansion (CTE). Competition between different materials, each with their own CTE, can push optic systems out of focus when the system’s temperature changes. The use of low CTE materials like Invar, carbon fiber composites, and silicon carbide help reduce these temperature effects. Unfortunately, they each have drawbacks such as the high density and low corrosion resistance of Invar, the polymer outgassing of carbon fiber composites, and the low fracture toughness of silicon carbide. In comparison, ALLVAR alloys shrink when heated, known as a negative thermal expansion (NTE), and have low density, high corrosion resistance, high ductility, and do not outgas. This NTE behavior, down to -16 x 10^-6 °C-1 at room temperature, offers a new way to athermalize optic systems by combining NTE alloys with positive CTE materials. The NTE alloy can compensate for a positive CTE material to achieve a desired CTE. Here we evaluate ALLVAR alloys as a potential material for optics applications.

The Liverpool Telescope group have been designing astronomical instruments for the LT and other 2-4m class telescopes for a number of years. This paper covers a variety of issues which need to be addressed in order to benefit from the unique advantages of 3D printing. In particular we discuss our experience of designing, building and testing a simple prototype structure that is analagous to a simple reflecting grating spectrograph.

The current quest for higher resolution and sensitivity for Astronomy and Earth Observation space missions is leading to larger entrance apertures for future optical payloads, resulting in new technological challenges in terms of optomechanical manufacturing, integration and testing. Ensuring feasibility and minimizing schedule impact of tight manufacturing and integration constraints or mitigating adverse in-orbit effects, Active Optics encompasses a range of enabling technologies for future large optical space instruments.

We present here an updated status overview of our current R and D activities in Active Optics, ranging from deformable space-compatible components to full correction chains. Finally we will share our perspectives on the way-forward to reaching technological maturity and ensuring implementation within future large optical missions.

The Optical Engineering and Fabrication Facility (OEFF) at the College of Optical Sciences, University of Arizona has successfully fabricated a 6.5m primary mirror and conducted integration and testing (I & T) of the primary mirror and telescope cell assembly for the University of Tokyo Atacama Observatory. The mirror has been fabricated using a new facility and advanced technologies developed by the group, including fabrication process optimization, a super-stable optical metrology support, infrared and visible metrology with high accuracy, and interferometry. Fabrication process optimization has simulated the entire fabrication process from the initial grinding to final polishing to specification, and optimized the tooling, frequency of metrology, and estimated convergence. Through the project the new process optimization successfully demonstrated the performance and guided the process in a deterministic way. The 6.5m primary mirror is made of E6 bolo-silicate glass with a honeycomb structure. Due to the scale it requires a mechanically and thermally stable metrology support to ensure highly accurate metrology. The new metrology support has demonstrated its extremely stable force stability and thermal stability over the project period. Metrology of large optics is always a challenge and the OEFF group has made outstanding advancement in IR and visible metrology and applied them seamlessly during the mirror fabrication with extremely low uncertainty. By applying the newly developed facility and technologies, the OEFF group successfully fabricated the 6.5m primary mirror in less than 7months, which is about 3 times faster than past 6.5m mirror fabrication at UA. After fabrication the mirror was integrated to the telescope cell and the primary mirror cell assembly has been tested using optical metrology to identify the static and dynamic behavior of the system. The testing includes support actuator influence functions, the nominal support force set, bending mode correction, and assessment of deliverable image quality. This paper presents the technical aspects of the mirror fabrication, advancement of metrology and I & T of the 6.5m primary mirror assembly.

The Richard F. Caris Mirror Lab at the University of Arizona continues the production of 8.4 m lightweight honeycomb segments for the primary mirror of the Giant Magellan Telescope. GMT will have a center segment surrounded by six identical off-axis segments, plus an additional off-axis segment to allow continuous operation as segments are removed for coating. Production highlights of the last two years include the spin-casting of Segment 5, preliminary polishing of Segment 2, and completion of the rear surface processing for Segments 3 and 4. We completed a preliminary design of the significant modifications of the test systems required for Segment 4, the center segment. We finished an upgrade of the 8.4 m polishing machine; both the upgrade and experience gained with Segment 1 have contributed to much faster polishing convergence for Segment 2. Prior to polishing Segment 2, we verified the stability and accuracy of the measurement systems by re-measuring Segment 1, achieving good agreement among multiple independent tests as well as good agreement with the original acceptance tests of Segment 1.

Green light for the construction of the 39-m aperture Extremely Large Telescope (ELT) was given by the Council of the European Southern Observatory (ESO) on Dec 4th, 2014. Procurement of the key elements, especially the optics, the dome and structure and the glass substrates, was soon after initiated by ESO team. Safran Reosc is proud to have been awarded all the key optical polishing and testing contracts with:

2015-07: the contract for thin glass petals of the Adaptive Optics M4 mirror unit,

2016-07: the contract for polishing the 4-m secondary convex mirror M2,

2017-02: the contract for polishing of the 4-m tertiary mirror M3,

2017-05: the contract for polishing and integration of the 931 1.45-m hexagonal segments constituting the giant 39-m primary mirror assembly M1.

This paper reports Safran Reosc’s work progresses along these four contracts with their various challenges and more specifically those related to the mass production of the M1 segments.

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs.

We describe the DESI corrector optics, a series of six fused silica and borosilicate lenses. The lens diameters range from 0.8 to 1.1 meters, and their weights 84 to 237 kg. Most lens surfaces are spherical, and two are challenging 10^th-order polynomial aspheres. The lenses have been successfully polished and treated with an antireflection coating at multiple subcontractors, and are now being integrated into the DESI corrector barrel assembly at University College London.

We describe the final performance of the lenses in terms of their various parameters, including surface figure, homogeneity, and others, and compare their final performance against the demanding DESI corrector requirements. Also we describe the reoptimization of the lens spacing in their corrector barrel after their final measurements are known. Finally we assess the performance of the corrector as a whole, compared to early budgeted estimates.

The European Extremely Large Telescope (E-ELT), with its primary mirror diameter of 39 meters, will be the largest optical/near-infrared telescope in the world and will allow scientists to investigate important unsolved issues of the universe.

The dome and telescope (DMS) are designed to ensure high performance in one of the most seismic active areas in the world, Cerro Armazones in Chile.

The Dome diameter is 86 m and sits on the top of a stiff concrete pier, which has been designed with horizontal seismic devices to reduce the seismic accelerations on the structures. The isolation system consists of a combination of High Damping Rubber Bearings (HDRBs) and lubricated spherical bearings.

The Telescope structure has been designed to be adaptive, during operation it is extremely stiff with low damping to guarantee the pointing and tracking (fixed condition) and when subjected to strong earthquakes it is flexible with high damping (isolated condition) to reduce the accelerations on the mirrors and instruments.

To fulfill these requirements, a 3D adaptive seismic isolation system has been designed with unique features. The telescope natural frequencies and damping change suddenly when the telescope is subjected to a 1-year return period seismic event, which is the maximum threshold acceleration acceptable without isolation. In the isolated configuration, the telescope frequencies range between 0.3 Hz (isolation frequency) and 30 Hz (highest frequency of interest), while in the fixed configurations the frequencies range between 2.6 Hz and 30Hz.

The vertical and horizontal acceleration reduction is obtained with special devices designed for this type of applications.

This paper presents the design and shows the results of the sophisticated nonlinear time history analyses performed on the DMS. The large finite element models consist of about 75000 nodes and over 110000 elements and include nonlinear spring damper elements calibrated experimentally to model the vertical and horizontal behavior of the seismic devices.

The new deployable tertiary mirror for the Keck I telescope (K1DM3) at the W. M. Keck Observatory has been assembled, tested and shipped to the telescope site, and is currently being installed. The mirror is capable of reflecting the beam to one of six positions around the telescope elevation ring or to retract out of the way to allow the use of Cassegrain instruments. This new functionality is intended to allow rapid instrument changes for transient event observations and improve telescope operations. This paper presents the final as-built design. Additionally, this paper presents detailed information about our alignment approach in the attempt to duplicate the instrument pointing orientation of the existing M3.

The demanding science goals of future astrophysics missions currently under study for the 2020 Decadal Survey impose significant technological requirements on their associated telescopes. These concepts currently call for apertures as large as 15 m (LUVOIR), and operational temperatures as low as 4 Kelvin (OST). Advanced mirror technologies, such as those implementing a high degree of actuation at the primary, can help to overcome the challenges associated with these missions by providing in-situ wavefront correction capabilities. Active mirrors can also greatly reduce the cost/complexity associated with mirror fabrication as well as system I and T as on-orbit performance specifications can be achieved under a variety of test conditions (i.e. room/cryogenic temperatures, 0g/1g). JPL has significant experience in this area for visible/near-infrared applications, however future mission requirements create a new set of challenges for this technology. This paper presents design, analysis, and test results for lightweight silicon-carbide mirrors with integrated actuation capabilities. In particular, studies have been performed to test the performance of these mirrors at cryogenic temperatures.

For the development of the Focus Mechanism of the CLUPI instrument of the ExoMars 2020 mission, the CSEM implemented a design based on flexible structure technology and the use of Commercial Off-The-Shelf (COTS) components. This choice was essentially motivated by the availability of the miniature sensor and actuator components. Such approach presents many challenges such as:

the qualification of the OTS voice-coil motor and Linear Variable Differential Transformer (LVDT),
the implementation of a reliable launch locking system,
the design of a flexible structure mechanism compatible with harsh mechanical environment.

The present article describes each of the above problematics and the investigation carried by CSEM to find solutions meeting the mission needs and constrains.

The construction of the next generation of 40 m-class astronomical telescopes poses an enormous challenge for the design of their instruments and the manufacture of their optics. Optical elements typically increase in both size and number, placing ever more demands on the system manufacturing and alignment tolerances. This challenge can be met by using the wider design space offered by freeform optics, by for instance allowing highly aspherical surfaces. Optical designs incorporating freeform optics can achieve a better performance with fewer components. This also leads to savings in volume and mass and, potentially, cost.

This paper describes the characterization of the FAME system (freeform active mirror experiment). The system consists of a thin hydroformed face sheet that is produced to be close to the required surface shape, a highly controllable active array that provides support and the ability to set local curvature of the optical surface and the actuator layout with control electronics that drives the active array.

A detailed characterisation of the fully-assembled freeform mirror was carried out with the physical and optical properties determined by coordinate measurements (CMM), laser scanning, spherometry and Fizeau interferometry. The numerical model of the mirror was refined to match the as-built features and to predict the performance more accurately.

Each of the 18 actuators was tested individually and the results allow the generation of look-up tables providing the force on the mirror for each actuator setting. The actuators were modelled with finite element analysis and compared to the detailed measurements to develop a closed-loop system simulation. After assembling the actuators in an array, the mirror surface was measured again using interferometry. The influence functions and Eigen-modes were also determined by interferometry and compared to the FEA results.

The European Extremely Large Telescope (ELT) is a 39-m Class telescope with active and adaptive capability included into the telescope being developed by the European Southern Observatory (ESO).

The Telescope Secondary (M2) and Tertiary (M3) Mirrors are 4-metre class Zerodur mirrors close to 3.2 Tons that are passively supported by Cells with an 18 points axial whiffletree and a warping harness system that allows to correct low order deformations of the Mirrors. Laterally the Mirrors are supported on 12+2 points by Lateral Supports. In addition, the Cells have alignment capabilities by means of a high precision hexapod.

SENER has been contracted by ESO for the design, construction, validation and delivery of the ELT Secondary Mirror (M2) and Tertiary Mirror (M3) Cells.

The Cells’ mechanisms guarantee the alignment of the Telescope during observation while correcting optics deformations. In this process, a high precision hexapod will be responsible for aligning and tracking the mirrors and an active structure will be used to compensate errors in the mirrors’ surface. These are large-size critical elements of the Telescope that require extremely high precision levels to give the Telescope optimal image quality.

This manuscript describes the preliminary design and key aspects of the ELT M2 and M3 Mirrors Cells mechanisms, in particular the Mirror Suppor.

TNO is developing Deformable Mirror (DM) technology, targeted for aberration correction in high-end Adaptive Optics (AO) applications in the field of lithography, astronomy, space and laser communication. The heart of this deformable mirror technology is a unique actuator technology based on the variable reluctance principle. The main advantages of this technology are the inherent high reliability, linearity (>99%), and high efficiency in terms of force per volume and unit power. Based on this actuator technology TNO built and tested a prototype DM, with 57 actuators, and a mirror diameter of Ø160mm. The test results show a highly linear actuator response, with less than 1% hysteresis over a stroke of 40μm. Atmospheric aberration correction has been shown with these DM’s in a free space laser-communication bread board. The same actuator technology is also used in the application of a highly compact Fine Steering Mirror (FSM), with an overall volume of Ø27x30mm, with a Ø20mm mirror. This FSM is targeted for satellite-based laser-communication terminals. Furthermore, a design study has been carried out to show the scalability of this technology towards large (~Ø1m to ~Ø3m) adaptive (secondary) mirrors with several hundreds, up to thousands of actuators. In this paper these different DM and FSM’s are discussed, and the latest test results obtained with the DM prototypes are presented.

MATISSE is the mid-infrared interferometric spectrograph and imager for ESO’s Very Large Telescope Interferometer (VLTI). A core mechanism inside the Cold Optical bench is the photometric slider, that enables the choice of observation with or without photometric beams which is achieved by sliding in 4 mirrors or 4 beam splitters into the four telescope beams. To achieve the stringent requirements on beam precision -which asks for mounting pad differences of order of 1 micrometer- all optical components were mounted on a single body and one lapped surface. Test results on the final instrument showed behavior significantly outside specification suggesting contact point height differences up to 6 micrometer. Also repeatability was non-compliant. We will present the cause analysis, the suspected culprit, unsuspected side effects and the implementation of the final solution which lead to a photometric slider well within specification.

The CEA Cryo-Mechanism (CM) was created to actuate infrared instruments wheels equipped with filters, coronographs or diffractive optics. Based on an optimized integration of basic industrial components, the CM operates with a high positioning repeatability (down to ±13 arcsec) in infrared astrophysical environment (very low temperatures and under vacuum). In 2004, for the first light of the mid-infrared imager/spectrometer VISIR, 12 CM units were produced. Among them, 10 units are operating once every hour since 13 years with a very high reliability.

From 2010, the CM was improved with the goal of space missions. Today, the CM reaches the status of a flight model mechanism already delivered for the EUCLID space mission (launch expected by 2021). It is also derived into a cost optimized actuator so called ICAR that will be manufactured in approximately 20 units for the ELT-METIS ground based instrument.

This paper gives an overview of the CM design and its different configurations. The paper will describe more in details the different tests that were carried out on the Euclid-CM, covering performances, vibrations, electromagnetism, thermal cycles, exported torques and life-time tests.

We present the design and performance of a cryogenic, angle-scanned Fabry-Pérot interferometer for far infrared astronomical spectroscopy. Novel features of the design are discussed, and the spectral response of the instrument is modeled. Experimental methods being developed to validate the spectral response are presented.

The European Southern Observatory (ESO) is building the Extremely Large Telescope (ELT), a 40-m class telescope to be installed on top of the 3046 m high mountain Cerro Armazones in the central part of Chile’s Atacama Desert. Once operational the ELT will be the largest optical/near-infrared telescope in the world. Powerful facility instruments that can deliver the science cases for the ELT are under development. The instrument roadmap lists more than six scientific instruments, each of them in the 15-35 tons range. While the telescope optics operate at ambient temperature, the instrument optics structure and in particular the detectors will be cooled to cryogenic temperatures down to as low as 4 Kelvin. ESO is aiming to implement proven technologies and commercial off-the-shelf components to build the cryogenic infrastructure for the ELT instruments. A combination of open loop Liquid Nitrogen cooling and low-vibration mechanical cryo-coolers will be installed to provide the required temperature levels and cooling capacities. ESO’s vacuum and cryogenic standards required major updates in order to match with the needs and challenges of this new class of huge instruments, each of them coming with up to 50 m³ vessel volume and more than 5 tons cold mass.

The paper outlines the instruments vacuum and cryogenic requirements, gives a brief overview of the ESO vacuum and cryogenic standards, and of the ELT cryogenic infrastructure baseline concept. The current testing approach for selected standard components such as low-vibration cryo-coolers and vibration damping systems will be presented.

One of the major challenges of optical fabrication is measurement of the surface when first polished out, before its figure is within the capture range of interferometry. A high dynamic range instrument with good accuracy is needed to efficiently guide the processing. Our approach is to use the Software Configurable Optical Test System (SCOTS), a deflectometry technique that uses a camera and liquid crystal display to measure the surface slope. We describe the use of SCOTS in the fabrication of a 6.5 m on-axis mirror and an 8.4 m off-axis mirror segment (Giant Magellan Telescope primary). SCOTS has the dynamic range to measure high slope errors early in the mirror figuring process, with sufficient accuracy to corroborate later interferometric measurements. Accurately measuring low order figure errors with SCOTS requires careful calibration of the system geometry. Details of the data collection and processing, and comparison to interferometry measurements are presented.

We measured the influence functions of a 9-actuator warping harness of an ELT primary mirror segment prototype using a fiber interferometer. The compact setup consists of a stiff, lightweighted aluminium plate with a similar diameter as the segment (1.25 m), holding 24 fiber-fed collimators arranged in three concentric rings. We measure simultaneously the 24 absolute distances to the mirror surface with a nominal precision of 0.5 ppm. The recorded noise level in a quiet environment was below 50 nm rms. We found good agreement between the measured influence functions and the finiteelement model by the segment support manufacturer. These measurements were performed at ESO Garching in June 2017, with the “Absolute Multiline” metrology system.

Telescope design advancements are leading to the need for larger convex secondary elements, making the use of traditional refractive test geometries impractical. In response to requests for larger convex components, Harris has developed the Plano Holographic Aspheric Stitching Technique (PHAST)^[1], a novel metrology approach that offers versatility as well as improved performance for large convex components. This approach was conceived initially for the in-process testing of the Large Synoptic Survey Telescope (LSST) M2^[2], a 3.4-meter diameter convex asphere and has since been expanded to a versatile design that can be quickly modified to test multiple prescriptions with minimal cost and schedule impacts. The metrology system has facilitated the production of the largest convex optic that Harris has processed and tested.

The metrology approach is a sub-aperture stitching technique that uses a diffractive nulling element. This leverages the rapid production times of the lithography industry to reduce the lead time for test set assembly. For the most common convex component geometries, this test can be ready for use in as little as six months from receipt of specifications.

We will present the development and design of this test methodology. Existing PHAST systems are providing high resolution and accurate data while demonstrating the stability of the overall approach. In addition, the approach is capable of rapid reconfiguration to accommodate testing of multiple convex optics over a range of sizes and specifications.

Break through large astronomical telescopes of the near future (ELT, TMT, MSE, LOT, etc.) will be comprised of extremely large optical elements, requiring segmented primary mirrors. Optical performance of the primary mirror requires an optical shape with an accuracy of a fraction of a wavelength over the whole radius. This can be practically achieved by composing the largest primary mirrors of scores to several hundreds of individually actuated hexagonal mirrors. Multi-layered control of these actuators is performed over sensors observing the position of non-surface parts of these mirror elements. Alignment calibration or co-phasing to the front-surface is required. This procedure needs to be performed at the initial assembly and updated after each (scheduled) daily mirror replacement and to compensate for residual drift. Capital investment costs of these telescopes create the necessity to minimize the duration of maintenance during the valuable night time hours. TNO has developed an affordable instrument methodology, capable of delivering coordinates of each mirror element with respect to its neighbors during day time. This instrument combines nanometer accuracy/precision with low latency and meets the strict requirements of co-phasing the large multi-segmented telescopes of the future. This article describes the requirements, design and specifications of this instrument. TNO benefits from a rich heritage of designing world class optical instruments for science and industry. This metrology system takes advantage of the development of fast, full-field, time-domain, white-light interferometry, which has been demonstrated previously for in-line quality inspection at harsh industrial machining workshops.

Spectrographs in high-multiplex fiber integral-field spectroscopy tend to have fast large field-of-view camera systems in order to meet the desire of packing as many spatial elements and wide a spectral bandpass as possible, thereby maximizing the use of detector real estate. This, very often, leads to a camera design with a field flattening lens very close to the detector active area with tight tolerances in the relative alignment between those two, on the order of a few hundredths of a degree and millimeter. This requires dedicated optical metrology process, particularly in cases where a large number of spectrographs, on the order of 100 or more, need to be accurately and reliably aligned and integrated. We have developed such a metrology process for the 156 camera systems in the VIRUS instrument. We detail the working principle of this metrology process, the implementation for the VIRUS camera systems, and how it can be applicable to multi-lens camera system alignment and integration.

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the methods and results for the commissioning instrument metrology program. The primary goals of this program are to calculate the transformations and further develop the systems that will place fibers within 5μm RMS of the target positions. We will use the commissioning instrument metrology program to measure the absolute three axis Cartesian coordinates of the five CCDs and 22 illuminated fiducials on the commissioning instrument.

High-resolution spectropolarimetry is a useful astronomical technique, in particular to study stellar magnetic fields. It has been extensively used in the past but mostly in the visible range. Space missions equipped with high-resolution spectropolarimeters working in the ultra-violet (UV) are now being studied. We propose a concept of a polarimeter working with temporal modulation and allowing to perform Stokes IQUV measurements over the full UV + Visible range. The purpose of this article is to describe the polarimeter concept, two prototypes and the bench developed to perform on ground testing to establish the performances of this new polarimeter.

One of the highest scientific priorities for the ELT is to image and characterise Earth-like planets around Sun-like stars. This will be achieved with the dedicated planetary camera and spectrograph, ELT-PCS. As ELT-PCS will push current contrast limits for high-contrast imaging, R and D needs to be undertaken to ensure the top-level requirements for the instrument will be met. In this paper we discuss plans to progress the required R and D for the integral field spectrograph technology, with the aim of qualitatively determining the best contrast achievable with both a lenslet-array and an imageslicer based spectrograph. More specifically, we present progression of the design for a new bench spectrograph capable of accepting either of the two competing technologies as its input.

Astrophysical calibration sources which can be used for high-precision radial-velocity spectroscopy require a calibration with even higher precision and accuracy. Calibration of these sources can be achieved with a high-resolution Fourier-Transform-Spectrograph (FTS). The precision (~ 20 m/s) of the FTS is mainly driven by its reference, often a stabilized HeNe-laser. To reach an acceptable precision, either averaging over a large number of measurements or a better reference is needed.

We developed a setup including a Laser-Frequency-Comb (LFC) for referencing a high-resolution FTS. Due to the pulsed source specific evaluation methods have to be used to retrieve the spectrum properly. We extend the sub-nominal method used in absorption spectroscopy by showing an algorithm to determine the interferogram cut points from the interferogram itself, rather than calculating them from the repetition rate and reference laser wavelength. Furthermore, we show that line position errors measured from comb spectra are associated with amplitude variability and phase noise. We give an estimate of the measured line position stability for different evaluation methods (truncation, shifting, apodization, zerofilling) on scales not dominated by these errors.

In the frame of the test of NISP instrument for ESA Euclid mission, the question was raised to perform a metrology measurement of different components during the thermal vacuum test of NISP instrument. NISP will be tested at Laboratoire d’Astrophysique de Marseille (LAM) in ERIOS chamber under vacuum and thermal conditions in order to qualify the instrument in its operating environment and to perform the final acceptance test before delivery to the payload. One of the main objectives of the test campaign will be the measurement of the focus position of NISP image plane with respect to the EUCLID object plane. To simulate the EUCLID object plane, a telescope simulator with a very well know focal distance will be installed in front of NISP into ERIOS chamber. We need to measure at cold and vacuum the position of reflectors installed on NISP instrument and the telescope simulator. From these measurements, we will provide at operational temperature the measurement of references frames set on the telescope simulator and NISP, the knowledge of the coordinates of the object point source provided by the telescope simulator and the measurement of the angle between the telescope simulator optical axis and NISP optical axis. In this context, we have developed a metrology method based on the use of a laser tracker to measure the position of the reflectors inside ERIOS. The laser tracker is installed outside the vacuum chamber and measure through a curved window reflectors put inside the chamber either at ambient pressure or vacuum pressure. Several tests campaigns have been done at LAM to demonstrate the measurement performance with this configuration. Using a well know reflectors configuration, we show that it is possible to correct the laser tracker measurement from the window disturbances and from the vacuum impact. A corrective term is applied to the data and allows retrieving the real coordinates of the reflectors with a bias lower than 30μm, which is lower than the laser tracker measurement uncertainties estimated at 60μm. No additional error term of the laser tracker measurement is observed when using the laser tracker with the curved window and in vacuum, comparing with a classical use of the laser tracker. With these test campaign, we have been able to demonstrate the possibility to use a laser tracker to measure in real time during a vacuum thermal test the position of different mechanical parts into a vacuum chamber with an accuracy better than 60μm.

The James Webb Space Telescope is a large, deployable telescope that will operate at cryogenic temperatures at the Earth-Sun Lagrange 2 point. The Webb Optical Telescope Element (OTE) consists of 18 actively controlled Primary Mirror Segment Assemblies (PMSAs), an actively controlled Secondary Mirror Assembly (SMA), and an Aft-Optics Subsystem (AOS) that contains a fixed Tertiary Mirror and a Fine Steering Mirror. The OTE is combined with the Integrated Science Instrument Module (ISIM) to create the full optical train called OTIS (OTE and ISIM).

OTIS has recently undergone cryogenic vacuum testing in Chamber A at Johnson Space Center in Houston, TX. A key outcome of this test was to verify there is adequate range of motion in PMSA and SMA actuators to align them to AOS/ISIM under flight-like conditions. The alignment state of the PMSAs and SMA was measured using photogrammetry and cross-checked optically using a variation of a classical Hartmann test. In the “Pass-and-a-Half” (PAAH) configuration, fiber sources near the Cassegrain focus propagate light through the full optical train and small tilts on the PMSAs create an array of spots on the science instrument detectors, mimicking the effect of a Hartmann mask. Comparison of measured and modeled spot arrays provides the alignment state of the SMA and the global tilt of the primary mirror. This paper will discuss the methodology, testing, and analysis performed to measure the alignment state of OTIS using the Hartmann method and verify the primary and secondary mirrors can be successfully aligned on orbit to meet performance requirements.

The first large Fabry-Perot etalon (Ø35 cm) of the VTF instrument was coated successfully using IBS technique. The High Reflective (HR) coatings need to meet the reflectivity specifications (95 +/- 1%) over the entire wavelength range 520-870 nm and the entire aperture (Ø25 cm) and also preserve the plate's flatness and airgap uniformity between the two platesto be better than 3 nm RMS. The change of the figure error of the individual faces after HR coating was exceptionally small: For plate 1 (upper) it changed from 1.7nm RMS before coating to 2.12 nm after coating, no change at all for plate 2 (lower).

The Dark Energy Spectroscopic Instrument (DESI), currently under construction, will be used to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers, in turn, feed ten broad-band spectrographs. We will describe the broadband AR coating (360 nm to 980nm) that was applied to the lenses of the camera system for DESI using ion assisted deposition techniques in a 3 m coating chamber. The camera has 6 lenses ranging in diameter from 0.8 m to 1.14 m, weighing from 84 kg to 237 kg and made from fused silica or BK7. The size and shape of the surfaces provided challenges in design, uniformity control, handling, tooling and process control. Single surface average transmission and minimum transmission met requirements. The varied optical surfaces and angle of incidence considerations meant the uniformity of the coating was of prime concern. The surface radius of curvature (ROC) for the 12 surfaces ranged from nearly flat to a ROC of 611 mm and a sag of 140 mm. One lens surface has an angle of incidence variation from normal incidence to 40°. Creating a design with a larger than required bandwidth to compensate for the non-uniformity and angle variation created the ability to reduce the required coating uniformity across the lens and a single design to be used for all common substrate surfaces. While a perfectly uniform coating is often the goal it is usually not practicable or cost effective for highly curved surfaces. The coating chamber geometry allowed multiple radial positions of the deposition sources as well as substrate height variability. Using these two variables we were able to avoid using any masking to achieve the uniformity required to meet radial and angle performance goals. Very broadband AR coatings usually have several very thin and optically important layers. The DESI coating design has layers approaching 3 nm in thickness. Having sensitive thin layers in the design meant controlling layer thickness and azimuthal variation were critical to manufacturing repeatability. Through use of strategically placed quartz crystal monitors combined with stable deposition plumes, the manufacturing variability was reduced to acceptable levels. Low deposition rates and higher rotation rates also provided some stability to azimuthal variation.

The reflectivity of telescope primary mirror is one of the fundamental parameters that shows the telescope performance. However, it has been difficult to obtain absolute value, especially the wide range spectroscopic performance measured in-situ on the primary mirror due to the lack of suitable measuring instrument. To overcome this challenge, we developed a portable spectrophotometer to measure the absolute spectroscopic reflectivity of telescope primary mirror. Its small dimension and light weight enable in-situ measurement on the primary mirror. This spectrophotometer covers the spectral range from 380 nm to 1000 nm with 2 nm resolution. The incident angle to the measuring surface is 12 degrees. The measurement beam size is about 12 mm in diameter. To obtain the absolute value, we adopted the principle of V-N method for the spectrophotometer. A sequential measurement also enables us to cancel the instability of the instrument.

The Subaru Telescope primary mirror was recoated with Aluminum on October 20, 2017. It was the eighth coating work from its arrival at Maunakea, Hawaii in 1998 and was about four years from the previous recoating. Before the recoating work, the reflectivity measured with the spectrophotometer was 70~76 % (@400 nm), 75~80 % (@600 nm), and 73~78 % (@800 nm). The large dispersion of the reflectivity is from non-uniform contamination of the surface, especially from the accumulation of dust particles on the mirror.

After the fresh coating of Aluminum, the values returned to 92.1 % (@400 nm), 90.5 % (@600 nm), and 85.8 % (@800 nm) with standard deviation less than 0.6 %. There were the data taken at the outside of the vacuum chamber right after the recoating.

The great advantage of our spectrophotometer is its capability of getting absolute spectroscopic reflectivity of the primary mirror in-situ. We can continue to monitor the reflectivity of the primary mirror in-situ using this spectrophotometer, even after the primary mirror is mounted on the telescope. This helps us better understanding of the long-term reflectivity degradation.

Many optical surfaces such as space and telescope mirrors are historically "uncleanable" and extraordinary measures are utilized to remove, recoat and therefore subsequently realign astronomical telescope systems resulting in extensive downtimes. Others, such as those used in space systems are extremely sensitive to organic contamination and particulate and residue removal is critical to performance. In this paper we present some recent data and examples that the strip coating First Contact Polymer, resulting from R&D from our labs, restores astronomical mirrors to like new condition by cleaning in situ and provides superior cleaning & protection from recontamination for telescopes, space instruments and other technologically important surfaces. We will also present data that these polymeric systems clean to the atomic level and that Laser Induced Damage (LIDT) results indicate that it leaves no residue. We will present details and supporting evidence that that our polymers, that were a critical enabling technology in LIGO’s Gravity wave discoveries of 2016, can greatly extend the lifetime of current mirror coatings on large astronomical mirrors.

University of California Observatories has undertaken an effort to develop improved coatings for optical astronomy, both reflective and anti-reflective. We report of the latest developments in this program. This effort includes new interface materials between silver and protective over-layers, one of which (nickel oxide) shows great promise for enhanced durability and works well to λ~340nm, as shown by aggressive environmental stressing. In addition, we have been exploring atomic layer deposition (ALD) for building protective metal-oxide layers for silver-based coatings, using a new facility capable of coating optics up to 0.9-m in size. This new facility has just been delivered, but we have already obtained excellent uniformity with Al2O3 coatings across the full diameter. We are exploring different deposition parameters with the goal of achieving excellent thin films at lower temperature than typically used in ALD by employing both remote plasma enhancement and/or alternate oxidizing agents. We plan to explore nitride and fluorides also. Finally, we report on continued development and deposition of broad-band anti-reflection coatings based on silica sol-gel. These developments are particularly important with regards to the next generation telescopes and instruments, but of course could be applied to existing telescopes and instruments.

The Phase A study for the high-resolution spectrograph for the Extremely Large Telescope (ELT-HIRES) has been concluded in late 2017. We present the main outcome for a polarimetric light feed from the intermediate focus (IF) and a Nasmyth focus of the telescope. We conclude that the use of the IF is mandatory for high-precision spectropolarimetry. Among the description of the product tree, we present phase-A level opto-mechanical designs of the subunits, describe the observational and calibration modes, the PSF error budget, and the preliminary FEM structural and earthquake analysis.

An update on the development of a ray tracing polarimetric simulator to estimate the instrumental polarization including both the telescope mirrors and the optical elements of the polarimeter is reported. Trade-off strategies and ongoing solutions in view of the Phase B are outlined too.

Vertically aligned carbon nanotube arrays are world renowned for their excellent optical absorption properties. However, at low angles, they suffer from higher reflection coefficients, due to the aligned structure. NanoLab has researched the potential for carbon nanotube loaded paints, (now marketed as Singularity Black) to create a more randomized structure with high optical and infrared absorption that will have better grazing angle performance. Other drivers for the development of a paint version include the desire to apply these coatings in large areas, on lower temperature substrates, and at lower cost. This paper describes the structures necessary for highly absorbing black coatings, and reviews the approach and data collected for two products, Singularity Black paint and the vertically aligned nanotube coating adVANTA.

Parasitic light is an important issue in optical systems and may be responsible for huge limitation of final performances. Use of absorbing coated surfaces is known to be an efficient means to reduce such parasitic light sources and various solutions exist that can be applied to mechanical surfaces such as black paints, carbon nanotubes or surface passivation.

In this paper, we show how thin film multilayer coatings can be a solution to answer this problematic as it is possible to design accurate spectral response that presents a very low level of reflectance with a zero value of transmittance.

After a description of the design steps, we will focus on the realization of such sophisticated metal-dielectric multilayer stacks using dense coating techniques; in particular, we will show that master of refractive index of very thin metallic layers is an asset to achieve accurate performances and how in situ optical broadband monitoring allows excellent reproducibility of production processes even for few nanometers-thick layers required in metal-dielectric absorbers.

Spectral and angular measurements of different coatings solutions will be given on various types of substrates (glass or metallic). Environmental qualification tests and spectral characterizations are also presented showing the stability of the performances in severe conditions compatible with severe environment. In particular, coatings developed for various projects will illustrate this study.

Surface relief gratings are well-established elements for high power laser applications, e.g. ultra-short pulse compression. A binary submicron period profile, realized by e-beam lithography and reactive ion beam etching in a dielectric material, is utilized for nearly one-hundred percent diffraction efficiency. Because these gratings are manufactured without any replication techniques, a high wave front accuracy and a low stray light background can be achieved. Spectroscopic applications require additional properties, i.e. a larger spectral bandwidth and Off-Littrow operation. We present new approaches for surface relief gratings realized either via multi-level staircase profiles or exploiting sub-wavelength features. The RVS spectrometer grating in ESA’s GAIA mission is a prominent example where these techniques are already in use. The current contribution focuses on the results achieved during a pre-development performed for the MOONS instrument intended to operate at VLT.

From the ultraviolet to the infrared, modern astronomical spectrographs are workhorse instruments at any wide-purpose observatory, enabling both follow-up and survey science across all fields of astrophysics and astronomy. As the critical optical element of determining the performance of any spectrograph, the key parameters of the dispersing element —resolution, throughput, bandwidth, and dispersion — must all be optimized for highest performance of the instrument. There are a growing number of alternatives in the domain of diffraction gratings and dispersing elements thanks to the development of new technologies (from holography to lithography and micromachining). Some of these technologies are not specifically developed for astronomy, but have exciting potential applications in this field. In order to make the best design choices for new instrumentation, it is necessary to understand the advantages and the limitations of each technology. Although many of the new developments will naturally focus on instrumentation for the new generation of Extremely Large Telescopes, any new developments will leverage the scientific impact of the small and medium facilities as well. In this talk, the outcomes of a dedicated workshop organized in October 2017 will be reported. The goals of that workshop were to bringing together scientists and engineers involved in the design and construction of spectrographs with our commercial partners who help produce and develop the necessary technology.

We present the latest developments at HORIBA of large size and high performances diffraction gratings for astronomy and space application. A new facility, called NANO-structure Larger Area Master (NANOLAM), has been built at HORIBA France SAS (Palaiseau, France), dedicated to the production of the largest gratings in the world. This new facility allows us to design and produce very large gratings, in reflection or transmission with various possibilities of groove profiles and densities. From meter size pure holographic gratings up to 6000gr/mm on any substrate shape, to ion-etched transmission gratings competing favorably with VPH technology, HORIBA has developed the widest innovative diffraction gratings portfolio dedicated to astronomy application. The fused silica etched technology used to manufacture transmission gratings is unique and offer a number of consequent advantages over VPH technology such as a better wavefront, performances homogeneity or lifetime thanks to its bulky all glass material. This technology allows HORIBA to offer GRISMs (grating on a prism face) as well. Apart from these exclusive holographic and ion-etched capabilities, HORIBA is also offering ruled gratings, generally dedicated to infrared spectral range with low groove densities. Echelle grating and immersed grating are also part of the HORIBA new capabilities. In addition, HORIBA continues to develop another proprietary technology, the Variable Groove Depth (VGD) gratings that allows in a single grating a continuous blaze wavelength adjustment. All the HORIBA gratings product range is cryogenic compatible, TRL9 space qualified and shows the best straylight performances on the market. Finally, HORIBA is also currently performing several studies in partnership with laboratories and space agencies to further improve the state-of-the-art gratings straylight performances, as well as developing gratings on free-form surfaces.

Silicon immersion gratings will allow the Giant Magellan Telescope Near-IR Spectrograph (GMTNIRS) to achieve continuous coverage over the entire J, H, K, L and M photometric bands with resolution R~65,000 at J, H and K and R~80,000 at L and M. Gratings for J, H and K will be blazed at R3, while the L and M gratings will be blazed at R4 to achieve the desired resolution. The higher blaze angle of the L and M gratings requires that we use 150mm diameter substrates rather than the 100mm substrates that our standard process was built for. In order to accommodate the larger substrates we have constructed a custom UV exposure system for contact printing of grating lines, and constructed fixtures for coating and etching of the larger substrates. These updates to our process have resulted in the successful production of a grating for the GMTNIRS M-band.

With the recent development of new ultra fine aluminium alloys and progress in the field of directly machined freeform surfaces, diamond machined freeform gratings could play an important part in future spectrographs or integral field units, particularly at SWIR and LWIR wavelengths where the improved thermal performance of metal optics at cryogenic temperatures is well established. Freeform diamond machined gratings can offer a cost-effective, compact, and flexible alternative to gratings fabricated by other methods such as ion beam etching or complement these technologies. In this paper, both the advantages and limitations of 5 axis diamond machined freeform gratings are presented and potential applications are discussed.

ESPRESSO is a fiber feed ultrastable High Resolution Spectrograph designed to work in the Combined-Coudé focus of Very Large Telescopes (VLT). A high resolution (R~100000) and an ultra-high resolution (R~220000) mode will be available to collect the light coming of one VLT telescope. In addition, ESPRESSO has an observing mode which allows to collect light of 2, 3 or 4 VLT units. This mode can feed simultaneously the spectrograph using a 4x1 fiber combiner. In the combiner, the light from 4 octagonal fibers will be mixed when projected onto a square fiber, as a double scrambler device. Here it is presented the design, manufacture, integration and tests for the 4x1 combiner of the ESPRESSO Fiber Link.

We introduce a design for a tip-tilt sensor with integrated single-mode fiber coupling for use with the front-end prototype of the iLocater spectrograph at the Large Binocular Telescope to detect vibrations that occur within the optical train. This sensor is made up of a micro-lens array printed on top of a fiber bundle consisting of a central single-mode fiber and six surrounding multi-mode fibers. The design in based on a previous prototype that utilized a multi-core fiber with seven single-mode fibers.¹ With this updated design, we are able to achieve a better sensing throughput. We report on the modeled performance: if the beam is perfectly aligned, 69% light is coupled into the central single-mode fiber feeding the scientific instrument. When the beam is not aligned, some of the light will be coupled into the outer sensing fibers, providing the position of the beam for tip-tilt correction. For this design we show that there is a linear response in the sensing fibers when the beam is subject to tip-tilt movement. Furthermore we introduce an adaptive optics testbed, which we call the Koenigstuhl Observatory Opto-mechatronics Laboratory (KOOL), this testbed currently simulates vibrations at the Large Binocular Telescope, and in collaboration we have extended it to allow single-mode fiber coupling tests.

The Dark Energy Spectroscopic Instrument (DESI) is under construction to determine the expansion history of the Universe using the Baryon Acoustic Oscillation technique. Over the life of the experiment DESI will measure the spectra of 35 million galaxies and quasars over 14,000 square degrees out to a redshift of 3.5. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5,000 robotic fiber positioners located at the prime focus. The fibers in turn will feed ten broad-band spectrographs covering the wavelength range from 360nm to 980 nm. Rapid and accurate targeting of the fibers is provided by precision theta-phi robotic fiber positioners. The fiber positioners are manufactured at the University of Michigan. Following assembly each positioner passes through a burn-in and verification sequence. We describe the testing of the positioners and discuss the performance achieved.

The ability to simultaneously position many ‘large’ payloads over the focal surface overcomes some of the potential barriers faced by future Extremely Large Telescopes. These devices, called ‘Hoverboards’ are currently capable of positioning payloads up to 3 kg over large focal surfaces (more than 3m). This is achieved by the combination of air pressure and vacuum forces, with either two or more Starbugs or stepper motors for precise positioning. Hoverboards could conceptually position compact deformable mirrors over the focal surface for implementing multi-object adaptive optics. Hoverboards could also position large fiber-based integral field units for multi-object spectroscopic surveys. We report on the development of a low-cost Hoverboard prototype suitable for flat and curved focal-plane surfaces for either the Giant Magellan Telescope or European Extremely Large Telescope.

MEGARA is an integral-field and multi-object medium-resolution spectrograph for the GTC 10.4m telescope, which was commissioned on June - August 2017. MEGARA offers two observing modes, the LCB mode, a large central IFU; and a Multi-Object Spectrograph (MOS) mode, composed by 92 robotic positioners carrying 7-fiber minibundles each. This paper presents the models and measurements developed for the alignment between the image of the telescope pupil and the 100-μm fiber cores during the integration and verification at the laboratory. On the one hand, the error in the positioner-minibundles assembly was optimized with the aim of achieving a fiber-to-fiber flux homogeneity better than 10%. On the other hand, the positioner pointing was characterized in order to achieve a pointing precision of 1/5 of the spaxel size (which has been designed to be 0.62 arcsec). The on-sky measurements obtained during the commissioning to verify our laboratory results are also presented.

Long-slit astronomical spectroscopy has various limitations when dealing with optimum slit width, atmospheric dispersion, extended source spectroscopy, etc. to name a few. Most of these issues can be solved by the use of optical fibers as the light carrier from the telescope focal plane to the spectrograph. The approach is technically and scientifically flexible in terms of instrument modularity and target acquisition. Implementation of Integral Field Unit (IFU) provides a continuous sampling of extended objects and has a distinct advantage over the single fiber. Using a microlens array in front of the fibers improves the sky coverage by increasing the fill factor. Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a novel instrument being built by the Inter-University Centre for Astronomy and Astrophysics, Pune for the 3.6m Devasthal Optical Telescope (DOT) constructed by Aryabhatta Research Institute of Observational Sciences, Nainital. Each of the 16 DOTIFS IFUs consist of 12x12 spatial elements (spaxels) distributed in a hexagonal honeycomb structure covering 8.7"x7.8" in the sky. Each IFU is made by a photolithography technique to transfer the corresponding microlens array pattern to create a mask which holds the fibers at the focal plane end of an integral field unit. These masks are aligned with the microlens array and fibers are inserted before gluing and polishing. The fiber array can be positioned with a peak positioning error less than 5 μm from the desired position within a fiber array, compared to a requirement of 10 μm. The slit end is made by wire EDM cutting technology and fibers are placed with an accuracy of ~0.3 pixels compared to a 6.75 pixel center-to-center gap between two spectra on the detector. In this paper we provide details of deriving requirements and error budgets. The process of photolithography and the use of generated masks to create an IFU are also discussed. The technique allows very cost effective mass production of IFUs which are very accurately matched with the corresponding microlens array.

Digital Micromirror Devices (DMDs) are programmable arrays of up two million tiny mirrors (typically 7 to 14 microns square) that can be tilted into one of two binary states. Typically, they are used to generate video images using digital light modulation, and are most commonly found in DLP projectors, televisions, and more recently 3D printers. In astronomical applications, DMDs can be used as a programmable slit mask in a spectrograph. This paper discusses the development of a new DMD controller, one optimized for near infrared astronomy applications; one that produces static frames, and operates at a much slower data rate with much lower power dissipation, and with fewer signal leads having much longer lengths, sufficient to significantly reduce the thermal load on the DMD.

Digital micromirror devices (DMDs) can be used as rapidly reconfigurable "slit mask" object-selectors in space- based UV multi-object spectrometers (MOS). There are several missions currently in the planning process, which are developing concepts for multi-object spectrometers. For example, both LUVOIR and HabEx plan to include such an instrument, working into the deep UV. Currently, DMDs are the only alternative technology to microshutter arrays, which were developed for the infrared MOS on the James Webb Space Telescope. However, the deep UV (100 - 300 nm) reflectivity of DMDs needs to be substantially higher for efficient mission operation. We have re-coated commercially available DMDs (which use aluminum alloy mirrors) with high reflectivity aluminum, which is protected from oxidation by a AlF3 overcoat. We found that DMDs remain functional after being re-coated and show a dramatic reflectance improvement in the region of 100 - 300 nm. The scattering properties of re-coated DMDs can be further improved by masking the gaps between individual micromirrors during the coating process.

In recent decades, spectroscopic capabilities have been significantly enhanced by new technological developments, in particular spatial reformatting. Spatial reformatting allows multiple functionalities: the observation of a larger area of sky, obtaining the spectra of all spatial elements under the same atmospheric conditions; modification of the shape and size of the field of view; focal-ratio conversion for the optimized coupling between the telescope and the spectrograph; increase in the spatial and spectral resolving power; the observation of multiple objects; homogeneity in the illumination; scrambling of spatial and/or phase induced structure with the instrument, thus improving the system stability; relocation of the exit pupil, especially important for telecentric systems. The impact of reformatting and the breadth of science cases is so great that many alternative methods and technologies have been proposed: image slicers using refractive or reflective solutions; optical fibers with different core sizes and geometries; microlenses used in isolation or combined with fibers and more recently, photonic devices such as Photonic lanterns to produce modal decomposition. In this paper, a comparison between all currently available options is presented, with a detailed analysis of their advantages and limitations and a proposal for a new reformatter combining slicers and photonic devices. This proposal presents the advantages of the other alternatives and additionally offers: minimization of focal-ratio degradation; produces image and modal decomposition; improves the throughput along the spectral range, increases the spectral resolving power and adds the functionality of scrambling. All of these advantages are combined in a system where photonic and astronomical instrumentation capabilities are joined in an innovative solution with many applications, like for example, the Extremely Large Telescope.

One of the most useful techniques in astronomical instrumentation is image slicing. It enables a spectrograph to have a more compact angular slit, whilst retaining throughput and increasing resolving power. Astrophotonic components like the photonic lanterns and photonic reformatters can be used to replace bulk optics used so far. This study investigates the performance of such devices using end-to-end simulations to approximate realistic on-sky conditions. It investigates existing components, tries to optimize their performance and aims to understand better how best to design instruments to maximize their performance. This work complements the recent work in the field and provides an estimation for the performance of the new components.

One of the highest scientific priorities for ESO's Extremely Large Telescope is imaging and characterising Earth-like planets around Sun-like stars, requiring contrast ratios of 10^-9 only achievable through a combination of extreme adaptive optics, advanced coronagraphy, and data post-processing. The dedicated planetary instrument ELT-PCS uses an integral field spectrograph to simultaneously obtain a homogeneous set of spectra over a two-dimensional field on the sky. Here we present the design and early results from prototyping activities for a lenslet-array and an image-slicer based IFU that are being studied in the context of the ELT-PCS R and D. In particular for the image slicer we investigate classical polishing techniques, like used for SINFONI and SWIFT, and diamond machining.

The Optimal Optical CoronagraphWorkshop at the Lorentz Center in September 2017 in Leiden, the Netherlands gathered a diverse group of 30 researchers working on exoplanet instrumentation to stimulate the emergence and sharing of new ideas. This contribution is the final part of a series of three papers summarizing the outcomes of the workshop, and presents an overview of novel optical technologies and systems that are implemented or considered for high-contrast imaging instruments on both ground-based and space telescopes. The overall objective of high contrast instruments is to provide direct observations and characterizations of exoplanets at contrast levels as extreme as 10^-10. We list shortcomings of current technologies, and identify opportunities and development paths for new technologies that enable quantum leaps in performance. Specifically, we discuss the design and manufacturing of key components like advanced deformable mirrors and coronagraphic optics, and their amalgamation in "adaptive coronagraph" systems. Moreover, we discuss highly integrated system designs that combine contrast-enhancing techniques and characterization techniques (like high-resolution spectroscopy) while minimizing the overall complexity. Finally, we explore extreme implementations using all-photonics solutions for ground-based telescopes and dedicated huge apertures for space telescopes.

Direct imaging systems are now designed for specific telescope apertures and specific high-contrast diffraction 2D patterns. Current coronagraphic masks are not adaptive components, and different apertures and science requirements must result in different masks, which always come in a small number in a real-life instrument. Adaptive components would make it possible to adapt to changes in the aperture transmission (which will likely happen on a daily basis with the near future highly segmented telescopes, such as ESO's ELT), as well as to reconfigure at will the high-contrast area for different observation modes. In particular, the prospect of characterizing planets with a known position at a high spectral resolution pushes for adaptive coronagraphs capable of creating high-contrast in a small area of the image plane. Micro-mirror arrays are commercially available MOEMS that may be used as binary adaptive amplitude mask. They adaptively redirect light in either one of two directions using millions of micron-sized, bi-stable mirrors. Their spatial resolutions is compatible with 2D binary apodization patterns, in addition to Lyot stops. We have conducted a series of laboratory tests to assess the compatibility of an off-the-shelf micro-mirror array with high-contrast imaging requirements. This communication first presents the context and the scope of the project. It then details the results of our initial characterization of the device, in particular a measurement of the wavefront aberrations and of the level of scattered light that it introduces. Finally, it presents high-contrast point-spread functions obtained with this device, and summarizes the limitations of current components to derive a possible roadmap for the development of scientific-grade adaptive pupil masks.

Active coronagraphy is deemed to play a key role for the next generation of high-contrast instruments, notably in order to deal with large segmented mirrors that might exhibit time-dependent pupil merit function, caused by missing or defective segments. To this purpose, we recently introduced a new technological framework called digital adaptive coronagraphy (DAC), making use of liquid-crystal spatial light modulators (SLMs) display panels operating as active focal-plane phase mask coronagraphs. Here, we first review the latest contrast performance, measured in laboratory conditions with monochromatic visible light, and describe a few potential pathways to improve SLM coronagraphic nulling in the future. We then unveil a few unique capabilities of SLM-based DAC that were recently, or are currently in the process of being, demonstrated in our laboratory, including NCPA wavefront sensing, aperture-matched adaptive phase masks, coronagraphic nulling of multiple star systems, and coherent differential imaging (CDI).

High-contrast imaging (HCI) techniques appear like the best solutions to directly characterize the atmosphere of large orbit planets and planetary environments. In the last 20 years, different HCI solutions have been proposed based on coronagraphs. Some of them have been characterized in the laboratory or even on the sky. The optimized performance of these coronagraphs requires a perfect wavefront unreachable without active control of the complete electrical field (phase and amplitude) at the entrance of the instrument. While the correction of the phase aberrations is straight forward using deformable mirrors (DM), correcting amplitude defects is complex and still under study at the laboratory level. The next generation of HCI instrument either for ground-based (PCS instrument for ELT) or space-based (LUVOIR, HabEx) telescopes will require a practical and operational solution for amplitude corrections. The implementation of a DM located at a finite distance from the pupil is a simple solution that has been chosen by most of the projects. There have been only a few investigations on the optimization of the mirror positions for dedicated optical designs. In this paper, we give an intuitive approach that helps defining the best deformable mirror position in an instrument. Then, we describe its application to the THD2 and the performance in the laboratory that reaches a contrast level below 10^-8 at distance larger than 6 λ/D.

The objective of the Evanescent Wave Coronagraph (EvWaCo) project is to develop a new kind of simple and cost effective coronagraph, first for ground-based telescopes and then for space-based telescopes. The principle involves the tunneling effect to separate the star light from the companion light. The star light is directed transmitted toward a WaveFront Sensor (WFS) that measures the wavefront distortions in the immediate proximity of the occulting mask with minimum non-common path errors. The beam reflected by the mask propagates toward the Lyot stop and forms the images of the companion and of the star residuals on the camera.

The EvWaCo concept has been demonstrated and this instrument is achromatic over the I-band of the Johnson- Cousins photometric system in unpolarized light. We have measured over this photometric band an Inner Working Angle (IWA) equal to 6 λ/D and contrasts of a few 10^-6 at distances greater than 10 Airy radii from the star Point Spread Function (PSF) center.

This paper describes the continuation of the project, from this setup of demonstration to the first prototype operating on the sky at horizon 2020. The objective is to show the capability of the full system to provide IWA and raw contrasts close to the state-of-art performance with the Thai National Telescope, by observing through an unobstructed elliptical pupil of major axis length equal to 1 m. The system will demonstrate over the full I-band an IWA close to 3 λ/D and raw contrasts equal to a few 10^-4 at a distance equal to the IWA from the PSF.

Phase-Induced Amplitude Apodization Complex-Mask Coronagraph (PIAACMC) designs provide the high-contrast required to directly image exoplanets over a region of interest at a small inner-working angle (IWA) while preserving planet throughput. A PIAACMC consists of a set of optics designed to work in relayed pupil and image planes, with several components which are challenging to fabricate. The optical design for PIAACMC is a two-stage set of aspheric optics responsible for lossless apodization by beam profile re-shaping, followed by a multi-zone focal plane mask (FPM) which alters the phase and amplitude of the incident light field across each zone using optical path length delays. Each zone corresponds to an optical path difference such that their combined effect in the science plane produces a broadband null - up to 20% in recent designs. A Lyot stop follows to further filter the diffracted starlight, or use it in a feedback loop for minimizing low-order aberrations such as wavefront tip and tilt. Finally, a set of inverse-PIAA optics may be implemented to restore the original beam profile to image the science plane unaffected by the distortions induced by the PIAA optics. The aspheric profiles of the PIAA and inverse-PIAA optics are reduced by the introduction of the multi-zone complex FPM; all of these are custom optics which require care to fabricate to within a few percent of their ideal design surface profiles. However, the cost of fabrication and implementation can be well worth the effort because in addition to small IWA performance, PIAACMC designs are robust against the increasingly complicated telescope pupil architectures being developed for future generation telescopes. PIAACMC has been successfully fabricated for and installed at the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument at the Subaru telescope, and, among other places, is being developed for segmented telescope architectures at the NASA Ames Coronagraph Experiment (ACE) testbed. We are now developing a design for MagAO-X, a 2000 actuator ExAO system on a 6.5 m telescope aperture at the Las Campanas Observatory in Chile; MagAO-X will deliver Strehl ratios above 70% with high-resolutions ranging between 14 and 30 mas. Similarly, the system contrast requirements are at least 10-4 between ~1 and 10 λ/D. MagAO-X, as well as the future generation Giant Magellan Telescope (GMT) offer opportunities to field-test design changes, and demonstrate the robustness of PIAACMC to telescope pupils with complicated architectures including segments, spiders, and secondary obscurations. We present designs for MagAO-X and GMT, discussing improvements in their design toward producing easily manufactureable components. Moreover for MagAO-X, we present the current state of fabrication for the PIAACMC with predictive models of performance from surface profile measurements of the custom optics.

The imaging quality and resolution of telescopes are deeply affected by the vibration that caused by electromechanical system and wind shake. Normally, vibration is caused by insufficient damping of the structure. In this paper, an active damper system based on linear motor is proposed to suppress vibration. The model of the whole control system is established at the beginning of this paper. LQR (Linear Quadratic Regulator) algorithm is proposed and the simulation is performed based on actual parameters of system. The results show that the system has a higher stability with higher Q value. The dynamic characteristics of the structure was obtained by analyzing the modal test data from accelerators. The experiments have been carried out to test the performance of the system. The results indicated that the active vibration damper can reduce the structure vibration 93.8% at 5.5Hz and increase the stiffness of structure.

The surface accuracy of the telescope focal plate plays a key role in high-precision astronomical observations. The 6- DOF parallel Focal Plane Pose Test Platform (FPPTP) is used to measure the deformation and surface accuracy of the focal plate in different space pose, and precise pose adjustment is an important indicator of the platform's performance. But the factors affecting the pose error of the platform are complex and difficult to describe accurately with mathematical model. Comparison of pose error compensation for the focal plate in different space pose using Generalized Regression Neural Network (GRNN) and Classification Regression Tree (CART) is studied in this paper.

The use of Additive Manufacturing (AM) processes for space and terrestrial applications is a constantly growing topic of interest from the main actors in the industry. In the perspective of its future developments in the space field and for terrestrial applications, CSEM tackled the challenge of producing compliant structures based on SLM (Selective Laser Melting). In this framework, high performance stainless steel flexures with thickness below 380 micron offering bending fatigue resistance above 15 million cycles under realistic load cases were produced. On the other hand topology optimization software and specific design rules are applied to produce optimized structural parts and monolithic compliant structures. The second part of this paper describes the successful redesign of electrical SlipRings Assemblies (SRA) rotors intended for space applications. This project was run jointly with RUAG Space Switzerland, based on their expertise in the field of space grade SRAs and thanks to the know-how developed by CSEM in the field of AM-based mechanical (re)design. The novel architecture based on the combination of additive manufacturing, casting and remachining enables a significant reduction of the manufacturing and assembly costs and risks.

This work is focused on the analysis of optomechanical mountings based on hexapodal kinematics architecture to obtain efficient supports and proper alignment of an optical device. It has been implemented a parametrized approach considering different conditions of load in terms of operative and survival conditions for the analysis. The project is organized in the following steps:

Definition of the structure with all the geometrical parameters as input for the code. Any type of initial condition (dimension and shape) can be considered starting from the kinematic chain between each part.
Definition of all the parameters required for the analysis. All the physical proprieties of the materials are defined in terms of mechanical and thermal behavior.
Definition of the proper mesh, with the selection of proper elements type, boundary conditions and applied loads.

Thanks to these three steps is possible to obtain practically any layout. Realistic survival and operational requirements of both ground and space based application has driven the analyses done. A comparison between the numerical simulations and a real example has been done to validate the modelling technique. The final result is a validated code with user’s interface, and a parametric analysis of the behavior of the optomechanical mountings based on hexapodal kinematics architecture.

The presented in this paper the IMCU (Intelligent Motion Control Unit) is part of the IMCS (Intelligent Motion Control System). That is a cost and time effective solution to implement complex and high performance motion control/test systems or prototypes. It constitutes a family of ready–to-use hardware and firmware components. A bespoke solution can be quickly and easily assembled from these components, corresponding to a particular combination of actuators and sensors (see [1]).

The paper present interesting alternative against a centralized configuration applying the developed Intelligent Motion Control Unit (IMCS) based on the modular design and distributed intelligence concept. It was already tested and implemented into different control structures of scientific instrumentation as Mosfire, Sofia, IAC etc. The IMCS is a cost and time effective solution to implement complex and high performance motion control/test systems or prototypes. It constitutes a family of ready-to-use hardware and firmware components. A bespoke solution can be quickly and easily assembled from these components, corresponding to a particular combination of actuators and sensors.

The Zwicky Transient Facility (ZTF) is a new time-domain survey project that will use a new camera with a 47 square degree field of view mounted on the Samuel Oschin 48-inch Schmidt telescope. To achieve good image quality over all sixteen 6K*6K CCDs (386mm＊395mm corner to corner), a trim plate was added in front of the existing cemented achromatic doublet to form an air-spaced triplet corrector. The trim plate is a Schmidt corrector using fused silica with 1348mm in diameter but only 15mm in thickness. The plate has been completed at NIAOT and already been mounted to the ZTF, the PSF seems very good.

The detailed fabrication process and testing to the trim plate from fine grinding to finish are presented in this paper, which includes CMM test, NULL test design, and Computer Controlled Polishing process developed at NIAOT.

This paper describes the technology of production and testing of mirrors for DAG Telescope (Doğu Anadolu Gözlemevi) produced by Belgium Company AMOS. JSC LZOS fulfils works on production and testing of three mirrors: primary concave hyperbolic mirror of diameter 4 m, secondary convex hyperbolic mirror – 764 mm and tertiary elliptical mirror with flat working surface with dimensions 890х650 mm. The primary mirror is produced from Zerodur, while the secondary and the tertiary ones – from Astrositall. Some auxiliary elements, containers and handling tools, etc. are also produced at JSC LZOS. Special aspects of mirrors machining and testing are also reflected in this article.

In this paper the design, analysis and development of an aluminum 1-m diameter prototype mirror for the telescope of the ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) mission are described.

ARIEL has been selected by the European Space Agency (ESA) as the next medium-class science mission (M4) to be launched in 2028. The aim of the ARIEL mission is to study the atmospheres of a selected sample of exoplanets.

The payload is based on a 1-m class telescope ahead of a suite of instruments: two spectrometric channels covering the band 1.95 to 7.80 μm without gaps, three photometric channels working in the range 0.5 to 1.2 μm, and a low-resolution spectrometer in the range 1.25 to 1.95 μm.

The telescope layout is conceived as an eccentric pupil two-mirror classic Cassegrain configuration coupled to a tertiary off-axis paraboloidal mirror. The telescope will be realized on-ground, i.e. subjected to gravity and at room temperature, but it shall operate in space, at 0 g, and at a temperature of about 50 K. For this reason, the telescope expected “as-built” in-flight performance has to be determined via a detailed thermo-elastic analysis.

A trade-off on the material to be used for manufacturing the 1-m diameter primary mirror (M1) was carried out, and aluminum alloys have been selected as the baseline materials for both the telescope mirrors and structure.

The use of metals, like aluminum alloys, is nowadays frequently considered for the fabrication of space telescopes observing in the infrared wavelength range. Small-size aluminum parts have been proved to be popular both for IR mirrors and structural components, but the manufacturing and stability of large metallic optics still have to be demonstrated. The production of a large aluminum mirror such as that of ARIEL is a challenge, and to prove its feasibility a dedicated study and development program has been started. A prototype, with the same size of the M1 flight model but a simpler surface profile, has been realized and tested.

Large-amplitude anomalous events have been observed in CCDs due to radioactive emission from high-index optical glasses, some producing charge-trapping like artefacts. We have identified the source of these events from one glass (Ohara S-YGH51) as α-particles from trace amounts of nuclides in the actinium decay series, parent ²³⁵U. We present measurements of the anomalous event rate for samples of 15 separate optical glasses with n_d ≥ 1.6. There is a variation in anomalous count rates of orders of magnitude range over these materials. Care should be taken in the selection of optical glasses to be located in close proximity to detectors.

The coefficient of thermal expansion of ZERODUR^® is optimized for an application temperature between 0°C to 50°C. Nevertheless ZERODUR^® can also be used at other temperatures. It has been shown elsewhere, that ZERODUR^® can be used at deep, down to cryogenic temperatures. At higher temperatures, the use of ZERODUR^® is restricted by the required accuracy of the coefficient of thermal expansion. As given in the ZERODUR^® catalog, the maximum application temperature is 600°C. Slight changes of the CTE may occur if ZERODUR^® is cooled down from application temperatures between 130°C and 320°C with rates that differ from the initial production annealing rate. This can be relevant in coating processes that work at temperatures above 130°C. In this paper, the effects of high temperature treatments on ZERODUR^® properties are discussed. Advices are given how to avoid material property or geometric changes if heat treatment cannot be avoided.

Since many years, SCHOTT has continuously published a broad range of statistical data on bending strength of ZERODUR^®. With this data it is possible to do lifetime calculations utilizing on threshold values for the bending strength of ZERODUR^® under various given surface treatments and environmental conditions. The bending strength of ZERODUR^® is mainly a function of the sub-surface damage (SSD) residues after final surface processing. Due to the nature of the bending strength of brittle materials, a surface that is free of sub-surface damage will have a significantly higher strength, compared to a surface with remaining SSD. Glass surfaces free of sub-surface damage need to be actively protected or handled with care to avoid any new defects like scratches that subsequently would reduce the strength of the surface. However, there is no data available that answers the questions: “Is every visible scratch automatically reducing the strength of the surface?”, “How easy is it to generate scratches on a ZERODUR^® surface?”. This publication discusses various sub-surface damage measurements on ZERODUR^® surfaces in relation to their surface treatment, including artificially generated scratches on polished and acid etched surfaces.

The development of smart devices based on new materials is a possible strategy for renew small telescopes which nowadays are loosing appeal. In this scenario, we propose a FPM (Focal Plane Mask) based on photochromic materials for MOS spectroscopy. Photochromic MOS masks consist of polymer thin films which can be reversibly made opaque or transparent in a restricted wavelength range using alternatively UV and visible light. Slit patterns can thus be easily written by means of a red laser directly at the telescope place, making possible to optimize their dimensions to the observing conditions and also any kind of shape can be obtained, included curved geometry, without mechanical limitations. To test the technique we designed and produced two different photochromic masks, which were successfully used at the national Copernico telescope in Asiago (Italy).

The Large Millimeter Telescope (LMT), located in Central Mexico, saw completion of the final construction phase in 2017 with the installation of the full 50-meter primary reflector, following three years of operation as a 32-meter facility. The task required the assembly and alignment of 96 primary surface segments, each comprising 8 laminated Nickel subpanels. These segments are installed on the antenna back structure in two concentric rings, expanding the existing 3- ring 32-meter configuration.

Prior to assembly of the new segments, a review of the original surface support system was carried out. Based on previous experience with the alignment and stability of the inner rings, it was decided to upgrade a large number of the early subpanel support and adjustment components. A key modification was the inclusion of lateral adjustment for subpanel support points, helping to minimize bending moments on the panels both during and after integration. Improvements in the ease of surface setting and greater surface stability were immediately observed following component overhaul. Form setting of individual segments was carried out at the LMT facilities in Puebla and again at the telescope site, using the iterative process developed previously that makes use of laser tracker surface measurements.

While the original implementation of the subpanel support system enabled the setting of individual segments to a mean surface error of around 30 micrometers RMS, this mean value was improved to around 20 μm for the entire set of 96 segments for the outer two rings, with the best segments coming in at around 18 μm RMS surface error. We believe this brings us close to the limit of achievable surface accuracy for the LMT design of laminated composite subpanels supported on simple mechanical differential adjusters.

We present an overview of primary surface improvements since 2011, and the main aspects of the LMT aperture expansion relating to the assembly and alignment of the surface segments for the outer two rings of the 50-meter primary.

Many of the current spectrographs available at state-of-the-art telescopes facilities, possess specifications that are strongly limited by the dispersing elements that are used. Therefore, a refurbishment of these devices would potentially increase the performances if innovative designs are considered. We propose a solution for designing stacked VPHG that is able to secure efficiently different spectra in a single shot. This could be possible considering parameters that are specific for a particular class of holographic material, the photopolymers, that are well known for bringing reliability and precise throughput. We demonstrate the applicability of our solution, through the example of the new spectrograph designed for the 1m telescope at SAO RAS. The spectrograph will cover a spectral range 444-706 nm with the spectral resolving power of R=4273-5176 and the throughput maximum of 64%. The working ranges of the gratings are selected to provide more diffraction efficiency around the main important lines used in astrophysics.

Direct laser writing is a powerful technique for the development of astrophotonic devices, namely by allowing 3D structuring of waveguides and avoiding in-plane crossings that can induce losses and crosstalk in multi-telescope beam combiners. In this work, a multiplexed device is proposed in order to increase the spectral bandwidth to hundreds of nm, for a central wavelength of 1580nm. Our device is fabricated by ultrafast laser inscription of type I waveguides in bulk IR-grade fused silica glass. A first part of the study was devoted to finding the optical fabrication parameters in terms of depth, speed and number of tracks needed to achieve an optimal waveguide, single mode in the near IR. A second part was focused to the fabrication of different optical lanterns, from one multimode input to several (4 or 16) single mode outputs. The optical chip consists of a multimode input slit-waveguide, that adiabatically converts into an aligned matrix of 4 or 16 single-mode channel waveguides, with a pitch corresponding to the detector pixel size. Two separations (20 μm and 64 μm) were studied, in order to avoid crosstalk between parallel waveguides (directional coupling) and from extracted flux into the detector (pixel crosstalk). A final part is dedicated to the spectrometer realization, based on the sampling of a stationary wave inside the waveguide.

We present a new single-shot, full-Stokes optical astro-polarimeter design using stress-engineered optics (SEOs). The SEO is a cylindrical glass window under static stress by radially-inward forces in three symmetrically-space regions, producing spatially-varying birefringence throughout (Spilman and Brown, Applied Optics IP, 46, 2007), and can be produced by using o-the-shelf supplies and some machining. By collimating light collected by a telescope through the SEO and then focusing it onto a detector, the system's point spread function (PSF) acquires a shape uniquely dependent on the full polarization vector of the input light (Beckley and Brown, Proc. SPIE, 757011, 2010). By measuring the imaged PSFs, the full-Stokes polarization states of all point sources (stars) in the field can ideally be determined from a single exposure and without division of amplitude techniques. Prior to our instrument, these techniques and technology had not yet been applied to astronomy. Aside from filter wheels and focusing elements, our instrument contains no moving parts. The instrument will operate by first taking a set of calibration exposures of 100% polarized light using swap-in polarizers in one of its filter wheels. Once the calibration images are taken, the polarizers are removed form the light path, and the science target (star) is imaged. Using techniques described in this paper, the calibration images allow one to determine the unknown polarization of the science target. This process is repeated in multiple photometric bands at visible wavelengths for color-dependent studies. The successful application of this polarimeter technology in astronomy would mark a step forward for increasing polarimetry efficiency (no temporal modulation required) and simplicity of instrumentation (no spatial modulation required). Contained in this paper are the on-sky commissioning results of our polarimeter on an 0:2m (8in) telescope at the University of Denver, and an in-depth look at the effect of Earth's atmospheric turbulence on the polarization-dependent PSF detection. We have also begun testing the instrument's capabilities in measuring both linear and circular interstellar polarization, and a look at the variability of historic polarized and unpolarized "standard" stars. Better understanding of the interstellar component of the polarization of stars and the nature of calibration stars are required for all future polarimetric measurements. The authors are grateful to the estate of William Herschel Womble for the support of astronomy at the University of Denver.

Compact yet highly functional optical components are desired in modern astronomical instruments targeted at low system cost and reduced maintenance complexity. Integrated photonic spectrometers based on planar lightwave circuits are attractive as the planar miniature device can provide high spectral resolution but also great robustness and flexibility in the design of spectrograph systems. Arrayed waveguide gratings (AWGs) have the potential to be adapted and optimized to function as compact spectrometers in astronomical spectrographs. In this work high-resolution AWGs based on low-loss silica waveguides have been designed, fabricated and characterized. The measured spectral resolution exceeds 104 with Δλ = 150 pm at 1548 nm. The insertion loss (including two times fiber-chip coupling) is merely 2.07 dB, amounting to a peak throughput of 62%. Adiabatic fiber taper is developed to bring down the mode field diameter of a standard single mode fiber to match the mode size of the designed waveguide, resulting in almost lossless coupling from the fiber to the waveguide. The free-spectrum range is 48 nm and the side-band suppression is 22 dB. The AWG is also polarization-insensitive. Rotating the linearly polarized input light by 180° results in a slight shift of the central wavelength ~ 30 pm. The excellent overall performance makes this AWG an ideal candidate as the key building block for the development of an integrated astronomical spectrograph module.

The Meteosat Third Generation’s extreme pointing requirements call for a highly stable bracket for mounting the Star Trackers. HB-Cesic^®, a chopped fibre reinforced silicon carbide, was selected as a base material for the sensor bracket. The high thermal conductivity and low thermal expansion of HB-Cesic^® were the key properties to fulfil the demanding thermo-elastic pointing requirements of below 1μrad/K for the Star Trackers mounting interfaces. Dominated by thermoelastic stability requirements, the design and analysis of the Bracket required a multidisciplinary approach with the focus on thermal and thermo-elastic analyses. Dedicated modal and thermal post-processing strategies have been applied in the scope of the light weighting process. The experimental verification of this thermo-elastic stable system has been a challenging task of its own. A thermo-elastic distortion measurement rig was developed with a stability of <0.1μrad/K in all three rotational degrees of freedom.

SWIMS-IFU is an image-slicer integral field unit designed for Simultaneous-color Wide-field Infrared Multi-object Spectrograph (SWIMS) of the University of Tokyo Atacama observatory 6.5m telescope. Its field-of-view, slice width and slice number are 17.2 ′′ × 12.8 ′′, 0.4 ′′ and 26, respectively. Due to the space limitation inside SWIMS, the IFU should fit in the dimension of 60mm×170mm×220mm. After finishing development of optical design, we have conducted tolerance analysis. The results show that the probability of vignetting of less than 5% is ∼90%, although at a slice of one side it drops to 50%. We plan to fabricate the mirror arrays monolithically by a ball-end milling with an ultra-high precision machine tool, and have conducted a demonstration process to prove its feasibility. Our requirement for shape error is less than 100 nm P-V and that for surface roughness is less than 10 nm r.m.s. Results of the latest demonstration satisfies the requirement. We will fabricate the mirror arrays and the support structures in 2018, and the IFU will be installed into SWIMS in 2019.

Several mirrors for the upgrade of the CRyogenic high-resulution InfraRed Echelle Sprectrograph (CRIRES) at the Very Large Telescope, were manufactured by diamond turning and polishing. These mirrors will be used in the crossdispersion unit (CDU) and the fore optics of the instrument. For background level reasons, the operational temperature of the CDU is set to 65 K. Therefore, the flat and spherical mirrors used in the CDU, which are made of melt-spun aluminum alloy Al6061, had to be artificially aged, to improve the dimensional stability at cryogenic temperatures. After diamond turning, magnetorheological finishing (MRF) was used for a deterministic shape correction and to remove the turning marks of the RSA6061 mirrors. To reduce the micro-roughness, a further smoothing step was necessary. A micro-roughness between 1 nm RMS and 5 nm RMS as well as shape deviations below 35 nm RMS were achieved. The mirrors were coated by inline magnetron sputtering with a high-reflective gold layer or protected silver, respectively.

We investigate the scattered light properties of a Luneburg lens approximated as a series of concentric shells with discrete refractive indices. The stepped Luneburg lens has been previously modeled at microwave wavelengths with full solutions for the electromagnetic field equations when the lens is of comparable size to the wavelength. We investigate the properties of a Luneburg lens at optical wavelengths using a geometric ray tracing technique. We develop a stack-based ray tracing algorithm with the python programming language that tracks all reflected and refracted rays generated at each optical interface. The code shows that a Luneburg lens with 40 steps and a refractive index power-law exponent of 0.55 will produce images of nearly all naked eye (<6) magnitude stars with an enclosed energy of 50% at a spatial resolution of 3.2 degrees. We find 72 cases of blended stars where a star with magnitude <6 falls within 3 degrees of angular separation from a star with magnitude < 1. The optical stepped Luneburg lens has promising applications for low-cost, continuous all-sky monitoring to obtain transit light curves of bright, nearby stars.

Future space X-ray mission concepts like STAR-X, AXIS and Lynx foresee optics with both high angular resolutions (HEW ~ 0.5 to 5 arcsec) and large collecting areas (~0.2-2.0 m²). These optics are very challenging to be produced and their manufacturing is under study. The Ion Beam Figuring (IBF) is one of the few techniques that is capable of correcting the residual manufacturing errors of the mirror shells and obtain the desired final optical figure. INAF-OABrera has two IBF facilities and is investigating the use of IBF on thin foils made by different materials, namely Silicon and Fused Silica. In this paper we describe the results obtained in a preliminary study on Silicon shells.

WEAVE is the new wide field multi-object and integral field survey facility for the prime focus of the 4.2 m William Herschel Telescope. WEAVE fiber-fed spectrograph offers two resolutions, R ~ 5000 and 20,000. The dual-beam spectrograph has two cameras: the blue one optimized for the wavelength interval of 366 - 606 nm and the red one for 579 - 959 nm. Each camera is formed by eight lenses, one aspherical and seven spherical. The lenses of the red camera are identical to the lenses of the blue camera only differentiated by the anti-reflection coating wavelength range. The diameter of the largest surface is 320 mm while of the smallest is 195 mm. INAOE, as a member of the collaboration is responsible of the manufacturing of the 14 spherical lenses and the collimator mirror. Here, we describe the main characteristics of WEAVE high precision cameras lenses, the manufacturing challenges giving the combination of OHARA glasses properties, dimensions and specifications. We discuss the solutions developed to achieve the very demanding specifications.

The use of 3M^TM Trizact^TM diamond tiled abrasive pads was proven as a cost-effective pre-polishing technique. Thanks to the low subsurface damages introduced it allows to speed up the polishing phases, reducing the amount of material to be removed. Nowadays, different kind of abrasive pads are available on the market and some of these are dedicated to the last phases of the surface finishing. In this paper, we present the results obtained with 3M^TM Trizact^TM Hookit^TM Film Disc 268XA as last step of the polishing phases. The test activity has been carried out on fused silica samples prepared with initial R_q around 50 – 70 nm. In particular, we focused on the wear rate of the pads, the material removal rate and the micro-roughness evolution, in dependence of several parameters as the amount of water, pH, velocity and pressure. The removal rate depends on the status of the abrasive pad and on the polishing conditions, while the micro-roughness of the surface can be decreased well below 1nm rms on millimetre scale. Moreover, a combined process of bonnet pre-polishing followed by 3M^TM Trizact^TM polishing has been proven as a cost-effective solution to realize super-polished optical surfaces.

A machining grating is remarkable for infrared use because it is difficult to get an ideal shape by traditional ruling engine. Canon has many kinds of gratings for the infrared on sale now by our processing technology. Our commercial grating is not only a conventional (reflection) grating but also an immersion grating. An immersion grating is very powerful and key device for the infrared high-resolution spectroscopy. It is sure that an immersion grating becomes next generation standard diffractive device for the infrared. However, there was no opportunity, which can be obtained easily before we enter this field. Our machined grating has very high absolute diffraction efficiency by the actual measurement. Furthermore, our surface flatness is the excellent compared before us. These are the performances already proved through our productions. Those will be the standard performance of a grating for astronomy. In this paper, we report that the performances and restrictions of machined grating in Canon.

The GMTIFS instrument requires multiple rotary mechanisms that will operate in a cryogenic environment. Angular precision up to one arc-second is required without the use of IR sources as part of an encoder. A general design that uses an annular conical rim bearing supported by three pairs of tapered pinch rollers has been proposed. One pair of pinch rollers is mounted on a flexure hinge to provide preload and accommodate thermal expansion. A pair of off set cylindrical cams carried by the rotor, and four capacitive distance sensors fixed to the stator are utilized to implement a resolver. This provides a measure of the rotor orientation that is insensitive to runout of the rotor. A prototype of this design was constructed and tested in the lab to investigate the effect of runout in the tapered rollers and assess the performance of the rim bearing and various resolver designs. We present the results of this testing.

HARMONI is a visible and near-infrared (0.47 to 2.45 μm) integral field spectrograph, providing the ELT's core spectroscopic capability at first light. A pre-optics subsystem provides four selectable spatial pixel scales, in addition to other beam conditioning functions such as shutter and pupil masks. For the validation of the mechanisms in charge of these functions (fast shutter and the plane mask wheel) we have planned some prototypes to test the design solutions.

The focal plane mask wheel sits in the input focus of the cryostat. It provides 16 user-selectable positions for masks (28x40 mm) used in observation. The key driver for this mechanism is the high repeatability (±2.5 μm) required, equivalent to ~1mas in the input focal plane. The IAC has previously designed, manufactured, tested and put in operation cryogenic wheels with high repeatability; however, the challenge of obtaining a wheel with such repeatability requires testing new concepts of detent positioning systems.

The shutter allows for exposures shorter than the minimum read time of the near-IR detectors and is needed for any CCD observations with the visible cameras. A dual shutter design is needed to achieve the necessary open/close times (<20 ms), but this also provides some redundancy and a graceful failure mode for this critical device. To mitigate risks on the proper behaviour of a fast cryogenics shutter a prototype based on a simple concept has been manufactured. We present the design and results for the performed cryogenic tests of a mask wheel and a shutter prototypes that we have developed.

Reflective optical system free from chromatic aberration is essential for astronomical instruments, which usually require wider wavelength coverage. However, it cannot always be the optimum choice compared with refractive optical system in terms of cost-effectiveness because mirrors require high surface accuracy and also because non-co-axial systems force tough alignment work. This dilemma could be overcome by a monolithic reflective optical system made entirely of cordierite CO-720, a ceramic material by Kyocera, which is the first material that offers both high-precision 3D-shaping and surface polishing for optical quality. This material also possesses a very low coefficient of thermal expansion (CTE) enabling a genuine athermal system useful for various astronomical applications. This athermality could make a significant breakthrough especially for cryogenic infrared instruments since optical systems made of cordierite are expected to keep as-built performance throughout the cooling process, providing extremely high wavefront accuracy that has never been possible at cryogenic temperature with conventional optical systems made of glasses or metals. In this paper, we report the first cryogenic optical testing of a small cordierite-made imaging optical system that was simply assembled with mechanical accuracy at room temperature. We confirmed that the diffraction-limited optical performance is kept even down to ~80K as built in the room temperature.

Application of CMOS image sensors with non-destructive readout capability have several advantages over current CCD sensors in detecting Near-Earth Objects (NEOs). They include detection of temporal changes, cosmic ray rejection, no charge blooming, expanded dynamic range, and lower dark current. Since wide field survey usually requires large mosaics, a “rolling shutter” operation simplifies the challenge of large mechanical shutters. Being able to readout parts of the field in destructive mode offers the possibility of providing guiding feedback to the telescope during exposure. We have carried out preliminary testing of a prototype CMOS camera built by Spectral Instruments Inc. on a one-meter telescope on Mt. Lemmon, Arizona as applied to rapidly moving NEOs. We have also demonstrated “post facto” guiding on a known NEO that significantly improves the signal to noise.

Over half of the light incident on the Earth from the Universe falls within the Far-Infrared (FIR) region of the spectrum. Due to the deleterious effects of the Earth's atmosphere and instrument self-emission, astronomical measurements in the FIR require space-borne instrumentation operating at cryogenic temperatures. These instruments place stringent constraints on the mechanical and thermal properties of the support structures at low temperatures. With high stiffness, tensile strength, strength-to-mass ratio, and extremely low thermal conductivity, carbon fibre reinforced polymers (CFRPs) are an important material for aerospace and FIR astronomical applications, however, little is known about their properties at cryogenic temperatures. We have developed a test facility for exploring CFRP properties down to 4 K. We present results from our ongoing study in which we compare and contrast the performance of CFRP samples using different materials, and multiple layup configurations. Current results include an evaluation of a cryostat dedicated for materials testing and a custom cryogenic metrology system, and preliminary cryogenic thermal expansion measurements. The goal of this research is to explore the feasibility of making CFRP-based, lightweight, cryogenic astronomical instruments.

Digital micromirror devices (DMDs) have the potential to revolutionize near infrared spectroscopy of crowded fields in astronomy. These devices, however, are not designed to operate at cryogenic temperatures as necessary for the infrared bandpass. The purpose of this study is to evaluate the viability of DMDs for use in infrared applications by testing the devices at cryogenic temperatures. In total, eleven DMDs were tested, each being cooled in a cryo-vacuum chamber to cryogenic temperature; approximately 90 K. Each device endured three cooldown and warmup cycles on average. Units tested include six stock, unaltered, DMDs from Texas Instruments™, as well as five re-windowed devices. Results indicate that stock devices function reliably at cryogenic temperature, however window-replaced devices had a high failure rate; likely due to contamination in the window-replacement process. Based on these results, it appears that stock devices perform reliably enough at cryogenic temperatures for reliable use in an instrument, but more research is needed into the re-windowing process before re-windowed devices are used within spectrographs.

The integrated cooling system with multi curved composite grooves on the surface of focal plate was designed to solve the problem that high-density heat resource is distributed on the focal plate. The new active heat dissipation experimental system was proposed considering the wide ambient temperature variation around the focal plate. The temperature field and deformation of the focal plate in the integrated cooling system under the environment of large temperature difference were analyzed by the simulation, and the active heat dissipation system for the focal plate was achieved by precise temperature control of the cooling medium. Meanwhile, the influence of active heat dissipation system on telescope observation was analyzed by the simulation. The simulation and experimental results suggested the integrated cooling system of focal plate can ensure the temperature of the focal plate constant and the deformation error of the focal plate is within the permitted range under the large temperature difference. And the new active heat dissipation system of focal plate can have a fast response speed and good adjustment ability in the condition of the varied ambient temperature, meanwhile, can effectively reduce the effect on the telescope observation.

The 1m telescope introduced in this paper is made for Nanjing University to do the study on the time-domain survey. The optical system of this telescope is a kind of the primary focus system. Tube designed for the 1m telescope is extremely important to support and define the optical elements and the 6K × 6K camera, because the alignment requirements between these assembles are pretty tight. Two types of the tube structure are designed in this paper, one is the cylindrical enclosed tube, the other is the open truss tube. The parameters of cylindrical tube and truss tube are optimized via the finite element analysis software ANSYS Workbench. Based on the mass, stiffness, cost performance etc. the performance of these two kinds of tube is compared to find a feasible and reliable tube design. Considering the main factors, truss tube is selected for the NU 1m telescope.

With the continuous exploration of the universe and astronomy’s development, the telescopes are bigger and bigger. Horizon structure is widely used in the modern large telescopes rack, which carries dozens, even thousands of tons of the rotary parts and demands high accuracy and good stability. Therefore, it is one of the key technologies for large telescope to develop the precision support technology integrated direct drive with large load, high stiffness, low friction, even frictionless. Magnetic suspension bearing has not only the advantage of non-contact, no friction, high rigidity, high precision, low power, low mechanical assembly requirements, but also is integrated with the driven torque motor, which simplifies the structure, reduces the cost. This paper explores one kind of active bias magnetic suspension bearing integrated with direct drive technology based on multidisciplinary design optimization (MDO), which provides a new choice and view for the modern large astronomical telescope tracking system.

GIANO-B is the high resolution near-infrared (NIR) spectrograph of the Telescopio Nazionale Galileo (TNG), which started its regular operations in October 2017. Here we present GIANO-B Online Data Reduction Software (DRS) operating at the Telescope.

GIANO-B Online DRS is a complete end-to-end solution for the spectrograph real-time data handling. The Online DRS provides management, processing and archival of GIANO-B scientific and calibration data. Once the instrument control software acquires the exposure ramp segments from the detector, the DRS ensures the complete data flow until the final data products are ingested into the science archive. A part of the Online DRS is GOFIO software, which performs the reduction process from ramp-processed 2D spectra to extracted and calibrated 1D spectra.

A User Interface (UI) developed as a part of the Online DRS provides basic information on the final reduced data, thus allowing the observer to take decisions in real-time during the night and adjust the observational strategy as needed.

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the universe using the Baryon Acoustic Oscillation (BAO) technique. The spectra of 35 million galaxies and quasars over 14000 deg² will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 robotically positioned optic fibres. The fibres in turn feed ten broadband spectrographs. Proper alignment of focal plate structure, mainly consisting of a focal plate ring (FPR) and ten focal plate petals (FPP), is crucial in ensuring minimal loss of light in the focal plane. A coordinate measurement machine (CMM) metrology-based approach to alignment requires comprehensive characterisation of critical dimensions of the petals and the ring, all of which were 100% inspected. The metrology data not only served for quality assurance (QA), but also, with careful modelling of geometric transformations, informed the initial choice of integration accessories such as gauge blocks, pads, and shims. The integrated focal plate structure was inspected again on a CMM, and each petal was adjusted according to the updated focal plate metrology data until all datums were extremely close to nominal positions and optical throughput nearly reached the theoretically best possible value. This paper presents our metrology and alignment methodology and complete results for twelve official DESI petals. The as-aligned, total RMS optical throughput for 6168 positioner holes of twelve production petals was indirectly measured to be 99:88±0.12%, well above the 99.5% project requirement. The successful alignment fully demonstrated the wealth of data, reproducibility, and micron-level precision made available by our CMM metrology-based approach.

The High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph (HARMONI) will be one of the instruments installed on ESO's 39-meter Extremely Large Telescope (ELT) at first light. The instrument will operate from 0.47 - 2.45 μm with Δλ/λ = 3,000 - 17,000. On-sky spatial pixels (spaxels) are divided between four spectrographs, each equipped with 11 transmission diffraction gratings to cover the ranges of wavelengths and spectral resolutions. These spectrographs will be cooled to ~140 K to decrease thermal radiation at longer wavelengths.

In all configurations, the diffraction grating will lose a greater fraction of scientific light than any other single optic in the instrument. Additionally, manufacturers are often unable to measure the fraction of transmitted light at HARMONI's longest wavelengths. For these reasons, we have developed a setup to measure the efficiencies of transmission diffraction gratings across HARMONI's bandpass. The setup uses modulated signals, a single detector, and a lock-in amplifier to minimize sources of systematic errors. A modified version of this setup may be used to measure stray light. These setups and initial results are presented.

A new 2.7-meter segmented secondary reflector has been delivered to the Large Millimeter Telescope (LMT) for coupling to the recently completed 50-meter primary. The segmented reflector was designed and manufactured by Media Lario S.r.l. in Lombardy, Italy, using the same laminated Nickel panel technology employed by the LMT for the full 50- meter primary surface.

Media Lario used their in-house coordinate measuring machine to adjust the surface during assembly, with the reflector panels facing upwards. As part of the Final Acceptance Review measurements of the surface were undertaken by LMT staff at the Media Lario factory, using both a laser tracker and photogrammetry. Measurements were also made of the electroforming mold for the central panel. The reflector was mounted on a rotating stand allowing surface measurements to be performed according to the respective gravitational load cases. Measurements at the Media Lario factory provided a useful reference for repeat data taken at the LMT site, since the reflector was shipped as a fully assembled unit, designed to require no further adjustment after leaving the factory.

In this paper we present the surface measurements conducted during the review, and comparisons of the observed gravitational load deformations with those predicted by FEA. Although the latter were often at the level of measurement uncertainty, we were able to verify specific cases, as well as performing a sanity check on the manufacturer's design analysis. The measurements confirmed final surface error values leading to reflector acceptance by the project. An RMS surface error of the order of 25 microns over the entire reflector was recorded at 60 degrees elevation using photogrammetry data after adjusting to the best-fit parabola, showing compliance with the LMT specification. Acceptance review measurements also provided a baseline for surface measurements at site prior to installation.

The Large Millimeter Telescope (LMT), located in central Mexico, saw completion of the final construction phase in 2017 with the installation of the full 50-meter primary reflector, following three years of operation as a 32-meter facility. The task was accomplished by adding two more concentric rings of surface segments to the existing three inner rings. Various techniques have been used previously to measure and align the 32-meter surface, including multiple laser trackers and far-field phased holography. Whilst the former method is time-consuming, requiring a full night to obtain a single surface map, holography provides low spatial resolution and requires removal of the secondary reflector for installation of the twin-horn receiver at the primary focus.

Photogrammetry has been used as an alternative measurement technique for the 32-m primary since 2015¹, and has gradually replaced our use of holography and laser trackers for this task² during recent years. Once the object has been targeted, photogrammetry maps may be obtained in around one hour. The technique does not require the installation of special equipment on the antenna, and has the advantage of allowing surface maps to be taken at any chosen elevation. The main drawbacks for the LMT application are environmental, since the antenna operates without an enclosure; strong winds may prevent use of the site tower crane for image taking, while the formation of condensation and frost on the reflector surface will "switch off" the reflective targets.

In this paper we discuss comparative measurements taken as the first outer segments were installed, and the use of photogrammetry to carry out the alignment of the fully installed 50-meter surface. At the time of writing this activity is still in progress, however full-surface alignment to the order of just over 100 microns was achieved quite quickly, with multiple elevation maps allowing the development of a usable 50-m active surface model for compensation of gravitational distortions.

An integrating sphere is often used to approximate a flat illumination field at some distant surface, but in the design of a tunnel which bridges the integrating sphere and the surface it illuminates, many opportunities exist to contaminate the geometric purity that would exist in the tunnel’s absence. It is shown that when constraining the tunnel/baffle geometry to a cylindrical tube with flat baffles and circular apertures, a potentially optimized first-order design exists and provides a suitable basis for more nuanced elaborations, such as the addition of secondary baffles or non-flat surfaces. A parametric design formula is derived and provided for real-world use, non-sequential stray light analyses with comparisons to alternate baffle designs is provided, and two reference designs as used in the CCD test facilities for the Large Synoptic Survey Telescope are shown.

As part of the telescope completion plan, the Large Millimeter Telescope (LMT/GTM) project replaced the hexapod positioner for the secondary (M2) mirror. The new hexapod was provided by Symetrie of Nimes, France. The particular challenges for the LMT/GTM hexapod are that it is both large and precise. After completion of the fabrication and internal contractor verification of the system, the project conducted a series of characterization tests, both at the fabrication facility and at the telescope site. During the factory tests, the project team tested the hexapod in both vertical and horizontal positions, verifying the motion range, accuracy, repeatability, and velocity, all at the maximum operational payload. Additionally, the team performed verification checks on the stiffness of the hexapod. The results were excellent, with calibrated errors of less than 5 microns in the translation degrees of freedom and less than 1 arcsec in the rotations, which was at the limit of the metrology of the tests. Following the successful factory test, the system was transported to the telescope site and the tests were repeated. While the calibration step was not performed during the site tests, the raw results were comparable to the factory values, clearing the way for installation on the telescope. The new hexapod was installed, along with a new M2 mirror, in the Fall of 2017 in advance of the LMT/GTM’s first observing season as a 50 m telescope. This paper presents the test program, the metrology approach, the characterization tests, the calibration method, and the final factory acceptance test results.

The Fast-steering Secondary Mirror (FSM) of Giant Magellan Telescope (GMT) consists of seven 1.1 m diameter circular segments with an effective diameter of 3.2 m, which are conjugated 1:1 to the seven 8.4 m segments of the primary. Each FSM segment contains a tip-tilt capability for fast guiding to attenuate telescope wind shake and mount control jitter by adapting axial support actuators. Breakaway System (BAS) is installed for protecting FSM from seismic overload or other unknown shocks in the axial support. When an earthquake or other unknown shocks come in, the springs in the BAS should limit the force along the axial support axis not to damage the mirror. We tested a single BAS in the lab by changing the input force to the BAS in a resolution of 10 N and measuring the displacement of the system. In this paper, we present experimental results from changing the input force gradually. We will discuss the detailed characteristics of the BAS in this report.

Fiber spectroscopic telescopes, such as LAMOST, require accurate alignment between the fiber ends and their corresponding celestial targets. In the measurement, the center of a light spot obtained through gray centroid method is regarded as the center of a fiber end. Nevertheless, we’ve observed that these two centers don’t coincide under wide visual angles when integrating sphere (Built in light source for bromine tungsten lamp) is used as light source. Basing on these phenomena we observed, this paper proposes a hypothesis that the maximum intensity of the light transmitted by the optical fiber to the end of the optical fiber is outside the end of the fiber. The intensity distribution at the output end of fibers under integrating sphere light source is simulated in this study. Keywords: accurate alignment

We present novel methods for mounting lenses in a pair of instruments that presented challenging optical and mechanical requirements. The first instrument is the replacement Natural Guide Star Sensor (NGS2) for CANOPUS at Gemini South, which incorporates an objective consisting of a stack of six lenses mounted in a common bore. A compliant radial spacer was used to eliminate lens decentre resulting from the additional radial clearance required to accommodate differential thermal strains between the low thermal expansion lenses and a common bore. In the same instrument, tangent contact toroidal spacers were deployed in place of traditional conical spacers to further reduce contact stresses in fragile calcium fluoride lens elements. The toroidal faces were specified with a 10μm profile tolerance to avoid possible edge contact between the spacers and lenses. We investigated milling and turning machining processes for the production of the spacers by comparing their results via Coordinate Measuring Machine (CMM) measurements. In the second instrument, Veloce, built for the Anglo-Australian Telescope, a lens decentre requirement of 40μm led us to develop a simple means of in-situ centring adjustment of the cell mounted lens. Physical testing of the finished instruments verified the performance of each of these methods. NGS2 produced images at the factory acceptance test in which 94% of encircled energy was captured by a single 16um detector pixel, surpassing the specification of 80%. Bench testing of Veloce during assembly showed that the adjustment mechanism allowed centring of the lens over a range of +/- 0.1mm with a precision of 5μm.

Measuring the position of the end of 4000 optical fibers on the spherical focal plate for the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope) optical fibers positioning system is one of the key problems for LAMOST. The accuracy of optical fibers positioning system is guaranteed by feedback from measuring the position of the end of optical fiber. The position of the end of optical fiber is measured by photogrammetry with precision calibration. However, given the complexities in the optical fiber focal plane and the fiber positioner, the accurate standard point is considerably difficult to obtain, which results in insufficient calibration accuracy. To solve this problem, a convenient calibration method based on the Flexible Planar Target (FPT) is proposed. In this method, each fiber positioning unit positions the fiber to 16 designed locations, which are relatively accurate. These points form a high-precision 2D point array that can be used as the planar target. In this manner, each fiber positioning unit can be regarded as a small high-precision planar target. All small high-precision planar targets are assembled to form the Flexible Planar Target (FPT), which is used for calibration. Experimental results indicate that this improved method can reach a higher precision than that of previous method.

High precision measurements of the filters bandpass used on wide-field imagers mounted on large telescopes is critical for type Ia supernovae studies. A dedicated spectrophotometric bench is used to re-measure the now decommissioned ugriz filters used for the SNLS on CFHT-MegaCam. A full characterization of the optical response with respect to the location on the surface and the angle of incidence was performed for each filter. Strong variation over the filter surface is observed. The impact of the actual response on the observation is evaluated and we demonstrate an improvement with respect to the previous published results (SNLS1 and 2).

When long term instrument stability is required, traditional alignment techniques based on bulky and/or flexible mountings can not be used due to their reduced stiffness. Mechanical alignment of optical systems is nowadays possible thanks to different 3D Coordinate Measuring Machines, as the Laser Tracker, the Articulated and Cartesian Arms. In this paper we describe the methods we considered for the integration and alignment of ESPRESSO, the very high resolution visible spectrograph for the ESO VLT, now under commissioning phase at Paranal Observatory. Different examples of the Front End (FE), the Anamorphic Pupil Slicer Unit (APSU), and the spectrograph itself will be provided, to demonstrate that it is possible to align an optical system with mechanical methods with minimal optical feedbacks, reaching in an almost ‘blind’ way the best optical performances.

We present the design, capabilities and applications of a cryogenic test facility for astronomical instrumentation located at ETH Zurich, Switzerland. This facility was designed, built, and commissioned with the purpose to support opto-mechanical performance measurements of cryo-mechanisms for astronomical instruments. In particular, the facility was developed initially to test the opto-mechanical stability and repeatability of the wheel-mechanisms for the ERIS/VLT instrument that are developed in house. However, the facility has a generic application portfolio and can be used for other development projects as well. The unique setup allows optical access from the warm end with short working distance to the cold elements of only a few millimeters. Electrical, mechanical, and liquid feedthroughs provide a flexible infrastructure for a large variety of thermal, mechanical, electrical and optical tests. To provide maximum mechanical stability, the cooling is provided by a low vibration pulse tube cooler that cools the facility down to approximately 8 K.

The goal of this project was to build a device capable of measuring both the specular reflectivity of black materials, as well as the Lambertian reflectivity of white materials over their full range of incident and observed angles, respectively. The MADLaSR (Multi-Angle Detection of Lambertian and Specular Reflectivity) is a device designed for specular reflectivity testing in the range of 10° < θ < 160° and for Lambertian reflectivity testing in the range of 10° < θ < 85°. The data collected from this device may be used to influence the design of optical systems, aerospace structures, or other devices in which maximum light control is a necessary consideration. This paper will discuss the design and functionality of the MADLaSR.

Traditional alignment techniques for optical systems are usually based on iterative procedures where each optical element is positioned and aligned with push-pull systems and the feedback is provided by the images acquired on the focal planes. The long-term stability of those optomechanical mounts can be critical and, in order to overcome this limitation a new mounting has been proposed together with a new alignment strategy based on the direct mechanical measurement of the optical surfaces. In this paper, the practical alignment limitations of this technique and the best possible strategy will be presented with the support of different experiments. A software used to predict the accuracy of the CMM measurements will also be described together with the validation results on a dummy optical system.

Traditional alignment techniques for optical systems are usually based on iterative procedures where each optical element is positioned and aligned with push-pull systems and the feedback is provided by the images acquired on the focal planes. The long-term stability of those optomechanical mounts can be critical and, In order to overcome this limitation a new mounting has been proposed together with a new alignment strategy based on the direct mechanical measurement of the optical surfaces. The contact between the probe and the surfaces of the optics can be a critical point and lead to different alignment strategies. In this paper, the forces applied by different Coordinate Measuring Machines (CMMs) will be presented together with a derived theoretical model. Moreover, the results of the damage tests performed on different optical elements will be shown and some general prediction rule will be presented.

Unlike conventional astronomical telescopes, there are telescope systems that have fixed altitude primary mirrors over which prime focus cameras track the sidereal motion. Examples include the Hobby Eberly Telescope (HET) in Texas and the South African Large Telescope (SALT) in Cape Town. These systems benefit from the economy of fixed primary mirrors but pose a unique challenge in active alignment control of such telescope systems using wavefront sensor feedbacks. To handle this situation, we developed a way of estimating orthonormal aberration coefficients over dynamically varying pupil geometries and implemented this as part of the multi-year upgrade of the HET. We detail the theory, implementation, and on-sky performance of this technique in the active alignment control of the HET based on the data collected during the HET upgrade commissioning and science operations since late 2015.

Over the past twenty-five years, ground based telescopes have made the leap from single, continuous primary mirrors to segmented apertures. This transition was motivated by the cost and complexity of large, monolithic optical surfaces. Space telescopes, driven by the same practicalities, are beginning to make this same transition. The challenge is to accurately phase these apertures such that they behave as a single monolithic mirror. Here we introduce a new method for this co-alignment based upon a classic knife-edge technique. The advantage of this method is: 1) it has a very large dynamic range, 2) it works with broadband light and is therefore very photon efficient, 3) it requires only a single mechanism and single sensor, 4) it works equally well with sparsely filled apertures as well as filled apertures, 5) it phases all the segments simultaneously, 6) requires no additional segment motion diversity for sensing. In this paper, we review the knife-edge method, provide context for the segment phasing problem, perform numerical simulations of the sensor, and provide preliminary laboratory confirmation of this method with a demonstration with a segmented deformable mirror.

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. To achieve this goal, it is crucial to guarantee that fiber positioners work properly under the extremes of potential operating conditions, including the full range of temperatures, high speed wind disturbance etc. Thermal testing provides valuable insight into the functionality of the fiber positioners that can be used to help mitigate poor performance at extreme temperatures and wind disturbance test provide guidance to design of ventilation system. Here, we describe the thermal and wind disturbance tests for DESI fiber positioners and how the test results helped improve the robustness of the positioners.

As compared to single-mode fibers (SMFs), photonic lanterns could ease the coupling of starlight to single-mode astrophotonic instruments. Here we investigate numerically the advantage of using lanterns as compared to SMFs for seeing-limited and low-order adaptive telescopes. We find the turbulence strength below which focal-ratio-matched photonic lanterns provide an average flux per output equal to that of a sole SMF. Lastly, we look into the advantage of having a low-order adaptive optics (AO) as a way of relaxing the demand on the lantern size and complexity.

Fibre Bragg gratings have been demonstrated to be a powerful tool with which to filter atmospheric emission lines from astronomical spectra. Multicore fibre technology has the potential to simplify the fabrication of fibre Bragg gratings, since all cores can be inscribed simultaneously rather than individually which is both time consuming and expensive to do. Solving the multicore challenge has fundamental implications for many fields outside of astrophotonics. To realise a working multicore fibre Bragg grating (MCFBG), all cores must be written with identical gratings providing uniform depth, Bragg wavelength and bandpass. However, to date, all multicore fibre Bragg gratings display a variation in the Bragg wavelength of the central cores compared to the outer cores. This seems to be a property of the multicore fibre itself, and is not due to the Bragg grating writing process.

We investigate the origin of these core-to-core variations using finite difference time domain and finite element simulations, combined with analysis of fabricated multicore fibre. We find that the ellipticity of the core, the size of the core, and the coupling between cores all affect the propagation constants. However, the dependence on ellipticity is very weak, and cores would have to be highly deformed in the manufacturing process for this to be a concern. A variation in radius of ~ 2:5% could account for the observed variation in propagation constants. However, the measured variation in the fabricated MCF is too small and does not display any radial trend. The coupling between cores is too small to change the propagation constants significantly, but even if it were significant any effect would be expected increase the Bragg wavelengths of the central cores, the opposite of what is observed.

The optical instrument used to measure and characterize sky quality at the IAC observatories is the DIMM (differential image motion measurements). The optical system and its mode of operation are relatively simple. It consists, basically, placing two equal apertures at the entrance of a telescope, in one of them an optical wedge is located. In this way, two beams of the same object are obtained which will lead to two on the focal plane of the telescope but laterally separated a few seconds arc. The complexity of this optical system lies in the "simplicity" of the plate used to separate the beams, it is a flat-faced wedge of a few minutes, and this is where problems arise when manufacturing it.

In this paper we present a new optical system concept to separate the beams. This is done using two optical flats tilted. The optical flats are not placed at the entrance of the telescope, but in the convergent beam. The optical design, manufacture and the test results obtained are presented.

Specific astronomical science cases could take advantage of VPHG devices with design and features tailored for achieving the best performances. The manufacturing process require materials where it is possible to precisely control the efficiency response, specially in complex optical designs, where the realization tolerances have to be strictly fulfilled. In this paper, we present an innovative design for the DOLORES spectrograph @ TNG as an example of complex VPHG (in GRISM mode) based on photopolymers. This dispersing element and its prisms were designed to cover, with low R, more than one octave and to disentangle 1st and 2nd diffraction orders avoiding the typical contamination. The ok-sky results are finally presented.

WEAVE is the next-generation optical spectroscopy facility for the William Herschel Telescope (WHT). It shows two channels (blue and red) and two working modes, a low-resolution (R=3,000-7,500) and a high-resolution (R=13,000- 25,000). The dispersing elements of the spectrograph are Volume Phase Holographic Gratings (VPHGs), two for the lower resolution mode and three for the higher resolution mode. Such gratings have a large size (clear aperture > 190 mm) and they are characterized by some key features, i.e. diffraction efficiency, wavefront error and dispersion that affect the final performances of the spectrograph. The VPHGs have been produced by KOSI based on the WEAVE design. After that, the VPHGs have been characterized, showing interesting results in terms of diffraction efficiency that reached peak values of 90%. As for the wavefront distortion, which is one of the critical aspect in VPHG technology, a different behavior between medium and high resolution elements was found. A larger wavefront distortion have been measured in the high resolution elements, because of the higher aspect ratio. A polishing process on the assembled VPHGs has been performed in order to reduce the wavefront distortion. Here, the results are presented and the specific issues discussed.

Due to the increase of astronomical projects and of their instruments, the request of large optics with higher optical performances does not stop growing. An important step in the manufacture of these optics is the deposition of high-precision optical coatings.
To answer to this request we developed coatings working at different angles of incidence and spectral ranges on large surface:

• - anti-reflective coatings for large lenses with strong curvatures,


• - dichroic coatings with sharp transition for large optics.

Main results will be presented on the basis of several examples of realization.

Spectroscopy is a key technique in astronomy and nowadays most major telescopes include at least one spectrograph in their instrument suite. The dispersive element is one of the most important components and it defines the pupil size, spectral resolution and efficiency. Different types of dispersive elements have been developed including prisms, grisms, VPH and echelle gratings. In this paper, we investigate the design and optimization possibilities offered by metallic freeform gratings using diamond machining techniques. The incorporation of power in a diffraction grating enables several functionalities within the same optical component, such as the combination of dispersion, focusing and field reformat. The resulting benefit is a reduction in the number of surfaces and therefore, an improvement in the throughput. Freeform surfaces are also interesting for their enhanced optical performance by allowing extra degree of freedom in the optimization. These degrees of freedom include the shape of the substrate but also additional parameters such as the pitch or the number of blaze angle. Freeform gratings used as single optical component systems also present some limitations such as the trade-off between optical quality versus field of view or the spectral range versus spectral resolution. This paper discusses the possibility offered by the design of freeform gratings for low to medium spectral resolution, in the visible and near-infrared, for potential applications in ultra-compact integral field spectrographs.

Volume Phase Holographic Gratings (VPHGs) are diffractive elements widely employed in the field of astronomical spectrographs. Photosensitive materials are used for the production of such elements and photopolymers represent a very interesting possibility. In particular, Bayfol^® HX solid photopolymers are high performance holographic materials that have been already used for the realization of VPHGs working in the visible for small spectrographs. Recently, a new set of GRISMs have been commissioned at BFOSC spectrograph in order to replace worn or outperforming ones and improve the instrument throughput. The first dispersing element covers the Hα band, while the second one is designed to work in the UV down to 330 nm. Issues related to the material absorption and to the light scattering were faced at short wavelengths. A step forward in the implementation of this class of holographic materials is the design of VPHGs working in the infrared. Two gratings were designed, covering the ZJ band (0.8 – 1.35 μm) and the JH band (1.05 – 1.9 μm). RCWA simulations were performed to find the parameters (refractive index modulation and thickness) required to obtain high efficiency in the target spectral ranges. Material absorptions are not negligible in the NIR and have to be taken into account during the design phase. Preliminary writing tests were performed giving interesting results. In order to make the design phase more reliable, a study of the dependence of the refractive index modulation on wavelength was performed.

Germanium Immersion Gratings (GIGs) may be an important component for a compact, high-resolution spectrograph for the infrared. Germanium’s large index of refraction reduces the length of the grating by a factor of four compared to conventional reflection gratings. Germanium transmits light from roughly 2 to 11.5 μm, which includes spectral regions largely unavailable from the ground because of molecules in Earth’s atmosphere. This combination makes GIGs a compelling technology for space missions focused on molecules in astrophysical environments. We are beginning testing of a GIG supplied by Canon, Inc., and anticipate eventual detailed testing of the Canon grating and a similar GIG supplied by LLNL. We also discuss potential science observations that demonstrate the significance of high-resolution, infrared spectroscopy from space.

We present the optical design of the ELT polarimeter in the context of the Phase-A study for HIRES. It is well known that in order to reduce the instrumental polarization and cross-talk, the optimal position for a polarimeter along the optical path of a telescope is the rotationally symmetric focus.

In the particular case of ELT this is represented by the intermediate focus (IF) below M4 which is not directly accessible and needs therefore a reimaging to a safety distance of at least 500 mm. The design of a transfer optics unit for such location is challenging due to the constraint of having an allowed vignetting area of maximum 5 arc min. We focus in our paper on two optical design solutions.

The first one is deploying a double Cassegrain system to reimage the IF, which includes the polarization optics and feeds the other ELT mirrors, redirecting the ordinary and extraordinary beams to the front end module (FE) onto the Nasmyth focus. This module comprises components for sky derotation, atmospheric dispersion correction (ADC), wavelength splitting in two bands (UBVRI, zYJH), field stabilization and conversion to f/20, dispatching the light into two pairs of fiber bundles to feed the HIRES spectrograph.

The other solution considers a fiber based compact IF module, using a Schwarzschild Collimator with Foster prism, ADC and beam splitters for the two spectral bands. The two polarized beams are sent by pupil imaging through four separate long fibers to the fiber link module of the spectrograph. There we convert the output fiber f ratio from f/2.5 to f/20.

Silicon immersion gratings take advantage of the high index of refraction of silicon (3.4) to significantly improve the performance and reduce the volume of near-infrared spectrographs. The immersion gratings we discuss here are produced by contact photolithography. Lithography is followed by plasma etching of a silicon nitride hard mask, which defines the pattern for wet etching of the silicon v-grooves in potassium hydroxide that form the blazed grating. We have shown that interference fringes between the photomask and the polished silicon nitride on silicon substrate produce a phase error in the completed grating. With our standard process, the lines in photoresist formed during the lithography step have a slope with an additional “foot” at the base of the line. The thickness of this foot can vary and may be partially etched away causing a shift in the position of the line during etching. To reduce the effect of the foot, we have added a plasma etch step designed to remove the foot prior to completing the silicon nitride etch. We have also found that thinning the photoresist to better control the profile formed during contact printing and subsequent etching results in very uniform gratings over a 125 mm grating length. We will also describe a method to predict the phase uniformity at the patterning stage, which allows us to pattern and evaluate the potential grating before etching, saving both time and material costs.

NASA's Europa Clipper will carry two cameras as part of the Europa Imaging System (EIS). Both the wide angle camera and narrow angle camera have identical focal plane modules, each containing a CMOS image sensor and patterned optical filter array. The filter array enables multispectral pushbroom imaging in six bands, spanning 380nm to 1000 nm, adding additional science capability for surface characterization and searching for evidence of recent activity. The EIS filter array is monolithic in construction, with all bands coated on a single substrate. Each stripe measures only 320 μm wide-equivalent to 32 pixels on the image sensor-leaving most of the field of view clear for full frame panchromatic imaging. Using photolithography, a mask is applied to the filter substrate and developed, leaving only the desired pattern exposed. The filter is then deposited onto the substrate and the mask removed. This process is repeated for each additional band on the array until all filters have been applied. The filters are then aligned with the image sensor rows using a machined metal housing, placing it as close as possible to the focal plane. As part of a technology development program to qualify them for space flight, several filters have been performance tested for resistance to radiation exposure, thermal cycling, vibration, and dry heat microbial reduction for planetary protection.

Astrophotonics is the new frontier technology to make suitable diffraction-limited spectrographs for the next generation of large telescopes. Astrophotonic spectrographs are miniaturized, robust and cost-effective. For various astronomical studies, such as probing the early universe, observing in near infrared (NIR) is crucial. Therefore, our research group is developing moderate resolution (R ~ 1500) on-chip photonic spectrographs in the NIR bands (J Band: 1.1-1.4 μm; H band: 1.45-1.7 μm). To achieve this, we use the concept of arrayed waveguide gratings (AWGs). We fabricate the device using a silica-on-silicon substrate. The waveguides on this AWG are 2 μm wide and 0.1 μm high Si₃N₄ core buried inside a 15 μm thick SiO₂ cladding.

To make the maximal use of astrophotonic integration such as coupling the AWGs with multiple single-mode fibers coming from photonic lanterns or fiber Bragg gratings (FBGs), we require a multi-input AWG design. In a multi-input AWG, the output spectrum due to each individual input channel overlaps to produce a combined spectrum from all inputs. This on-chip combination of light effectively improves the signal-to-noise ratio as compared to spreading the photons to several AWGs with single inputs. In this paper, we present the design and simulation results of an AWG in the H band with three input waveguides (channels). The resolving power of individual input channels is ~1500, while the overall resolving power with three inputs together is ~500, 600, 750 in three different configurations simulated here. The device footprint is only 16 mm x 7 mm. The free spectral range of the device is ~9.5 nm around a central wavelength of 1600 nm. For the standard multi-input AWG, the relative shift between the output spectra due to adjacent input channels is about 1.6 nm, which roughly equals one spectral channel spacing. In this paper, we discuss ways to increase the resolving power and the number of inputs without compromising the free spectral range or throughput.

Black coatings are used in infrared instruments for the suppression of stray and scattered photons. We previously reported on a diamond-like carbon (DLC) coating that exhibited extremely low outgassing for high vacuum applications¹. The nature of the plasma deposition process limits the shapes that can be coated to flat plates or openended tubes. Additionally, the IR reflectivity, though low, is highly specular, which can be problematical in certain situations. We have since examined a number of other surface treatments including paints and electrodeposited coatings using a hemispherical directional reflectometer. Specular and diffuse reflectance is reported as functions of wavelength and incidence angle. Some vacuum considerations will be discussed. We show the application of black coatings to the design of a light trap/air vent.

The Rapid Infrared Imager/Spectrograph (RIMAS) is an instrument designed to observe gamma ray burst afterglows. Dispersion in the moderate resolution mode (R~4000) is provided by ZnSe grisms: one covering the Y and J bands and the other covering the H and K. Each has a clear aperture of 44 mm. For the HK grism the blaze is 49.9° with a 20 line/mm period. The grooves cover an area of 69 mm x 45 mm.

The HK grism was diamond machined on the Precision Engineering Research Lathe (PERL) at LLNL. Chipping of the grooves increased from moderate to severe as the cutting progressed resulting in excess scattered light and reduced diffraction efficiency. High magnification optical microscopy and SEM of the cutting edges indicated damage to the tool caused by wear.

A comparison of the outcomes of ZnSe gratings and grisms machined at LLNL indicated that chipping was minimal in low blaze angle cuts but moderate to severe with the blaze angle near 45° as in the HK grism. Vendor records showed that the (100) crystal planes of the diamond were aligned parallel to the tool shank. Therefore the (100) planes are closely aligned with the cutting edge in low blaze angle tools but 45° off in the HK tool. We believe that this misalignment of the cutting edge with the (100) crystal plane in the HK tool produced excessive tool wear resulting in the chipped grooves observed.

We present the novel design of microfabricated, silicon-substrate based mirrors for use in cryogenic Fabry-Perot Interferometers (FPIs) for the mid-IR to sub-mm/mm wavelength regime. One side of the silicon substrate will have a double-layer metamaterial anti-reflection coating (ARC) anisotropically etched into it and the other side will be metalized with a re ective mesh pattern. The double-layer ARC ensures a re ectance of less than 1% at the surface substrate over the FPI bandwidth. This low reflectance is required to achieve broadband capability and to mitigate contaminating resonances from the silicon surface. Two silicon substrates with their metalized surfaces facing each other and held parallel with an adjustable separation will compose the FPI. To create an FPI with nearly uniform finesse over the FPI bandwidth, we use a combination of inductive and capacitive gold meshes evaporated onto the silicon substrate. We also consider the use of niobium as a superconducting reflective mesh for long wavelengths to eliminate ohmic losses at each reflection in the resonating cavity of the FPI and thereby increase overall transmission. We develop these silicon-substrate based FPIs for use in ground (e.g. CCAT-prime), air (e.g. HIRMES), and future space-based telescopes (e.g. the Origins Space Telescope concept). Such FPIs are well suited for spectroscopic imaging with the upcoming large IR/sub-mm/mm TES bolometer detector arrays. Here we present the fabrication and performance of multi-layer, plasma-etched, silicon metamaterial ARC, as well as models of the mirrors and FPIs.

Massively multiplexed spectroscopic stellar surveys such as MSE present enormous challenges in the spectrograph design. The combination of high multiplex, large telescope aperture, high resolution (R~40,000) and natural seeing implies that multiple spectrographs with large beam sizes, large grating angles, and fast camera speeds are required, with high cost and risk. An attractive option to reduce the beam size is to use Bragg-type gratings at much higher angles than hitherto considered. As well as reducing the spectrograph size and cost, this also allows the possibility of very high efficiency due to a close match of s and p-polarization Bragg efficiency peaks. The grating itself could be a VPH grating, but Surface Relief (SR) gratings offer an increasingly attractive alternative, with higher maximum line density and better bandwidth. In either case, the grating needs to be immersed within large prisms to get the light to and from the grating at the required angles. We present grating designs and nominal spectrograph designs showing the efficiency gains and size reductions such gratings might allow for the MSE high resolution spectrograph.

A new atomic layer deposition (ALD) tool has been designed, constructed, and tested to apply uniform protective coatings over a substrate 36” in diameter. The new tool, named the meter-scale ALD system (MSAS), employs a novel chamber design which utilizes a large substrate to be coated as a wall of the chamber. Conceptual design and implementation of this new tool are discussed with potential applications to large astronomical telescope optics, specifically protective coatings for silver mirrors, and other future large structures. In this work, aluminum oxide was deposited by thermal ALD using trimethylaluminum and water at a low reaction temperature of 60°C. Thickness uniformity across a 36” substrate is within 2.5% of the average film thickness. MSAS aluminum oxide deposition process parameters are compared with those of a conventional 4” wafer-scale ALD tool. The results show promising application of transparent robust dielectric films as uniform barriers across large optical components as well as multiple wafer assemblies encountered in semiconductor processing.

We report on an expanded catalog of total and specular reflectance measurements of various common (and uncommon) materials used in the construction and/or baffling of optical systems. Total reflectance is measured over a broad wavelength range (250 nm < λ < 2500 nm) that is applicable to ultraviolet, visible, and near-infrared instrumentation. Characterization of each sample's specular reflection was measured using a helium-neon laser in two degree steps from near normal to grazing angles of incidence. The total and specular reflection measurements were then used to derive the specular fraction of each material.

We present total reflectance measurements and Lambertian characterization of various materials that are commonly (and uncommonly) used as a screen for imaging system calibration (such as flat fielding). We measure the total reflectance of the samples over a broad wavelength range (250 nm < λ < 2500 nm) that is of interest to astronomical instruments in the ultraviolet, visible, and near-infrared regimes. A Helium-Neon laser was used to determine how closely the various materials' diffuse reflectance characteristics match that of a Lambertian surface.

In this work we present the coatings of the spectrograph red camera of WEAVE -the new multiobject survey facility for the 4.2m William Herschel Telescope. The initial requirements of WEAVE red camera lenses, with reflectances as low as 0.4% through the wavelength interval from 590 nm to 959 nm at angles of incidence of 18° +/- 17° represented a challenge for both design and production. Based on initial requirements, several solutions to the same problem were achieved and tested. The customized designs have been continuously improved through theoretical and experimental approximations. From transmittance measurements at normal incidence we developed a method to determine the reflectance at different angles of incidence. We show the designs and coating transmittance obtained for the four glasses on test runs to guarantee that the designs were achievable experimentally. Additionally, we present the reflectance obtained on the lenses of the the first four lenses of WEAVE red camera.

MEGARA is the new integral field unit (IFU) and multi-object (MOS) spectrograph successfully commissioned at Gran Telescopio Canarias, in August 2017. MEGARA provides spectral resolutions R (fwhm) ~ 6000, 12000 and 20000, via volume phase holographic gratings, at very high efficiency in both IFU and MOS modes. In the case of MEGARA main optics and pupil elements optics, the surfaces in contact with air have an anti-reflective (AR) coatings to minimize the Fresnel losses at the interface glass-air. In this work we present the designs and calculation of the total throughput of the optical system based in the transmission measurements of the AR coated witness samples. The results reflect the benefits of having implemented customized AR coatings for the mean angle of incidence on each surface as the measured throughput was better than the requirements. We analyze the effects of the pupil elements AR coatings for each spectral configuration.

We present concept and laboratory demonstration of high-contrast apodization baffle for instruments to be carried on exploration missions of the solar system. The primary science objective of the high-contrast baffle is to reveal escape of atmosphere on Mars, while other faint objects around blight sources are potential targets. We diverted heritages studied for exoplanet science and instrumentation to this work. The apodization in this work is realized by edge with microscopic Gaussian shaped structure. A simulation to confirm the concept and design of the high-contrast apodization baffle was carried out. Then, a baffle which was consisting of transparent flat substrate and thin film of aluminum on it was manufactured. The experiment was executed with He-Ne laser with wavelength of 633 nm. As the result, it was demonstrated that the apodization by the Gaussian edge is significantly working to improve the contrast. Achieved contrast is better than 10^-6.5 and 10^-8 in θ > 0.5 degree and θ > 1 degree, respectively. These results satisfy the requirement for remote sensing of the atmospheric less on Mars.

Proxima b is a terrestrial exoplanet orbiting in the habitable zone of our closest star Proxima Centauri. The separation between the planet and the star is about 40 mas and this is with current instruments only reachable with direct imaging, using a visual extreme AO system like SPHERE/ZIMPOL. Unfortunately, the planet falls under the first airy ring at 2λ/D in the I band, which degrades achievable contrast. We present the design, optical simulations and testing of an amplitude pupil mask for ZIMPOL that reshapes the PSF, increasing the contrast at r = 2λ/D about an order of magnitude. The simple mask can be inserted directly into the current setup of SPHERE.

Starshades, combined with future space telescopes, provide the ability to detect Earth-like exoplanets in the habitable zone by producing high contrast ratios at small inner working angles. The primary function of a starshade is to suppress light from a target star such that its orbiting planets are revealed. In order to do so, the optical edges of the starshade must maintain their precise in-plane profile to produce the necessary apodization function. However, an equally important consideration is the interaction of these edges with light emanating from our own Sun as scattered and/or diffracted sunlight can significantly degrade the achievable contrast. This paper describes the technical efforts performed to obtain precision, low-scatter optical edges for future starshades. Trades between edge radius (i.e. sharpness) and surface reflectivity have been made and small-scale coupons have been produced using scalable manufacturing processes. A custom scattered light testbed has been developed to quantify the magnitude of scattered light over all sun angles. Models have also been developed to make predictions on the level of reflected and/or diffracted light for various edge architectures. The results of these studies have established a current baseline approach which implements photochemical etching techniques on thin metal foils.

Future space-based observatories such as WFIRST will be equipped with high contrast imaging instruments designed to study extrasolar planets and disks in the absence of atmospheric perturbations. One of the most efficient techniques to achieve this goal is the combination of wavefront control and broadband coronagraphy. Being able to achieve a high contrast over a wide spectral bandwidth allows us to characterize the chemical composition of exoplanet atmospheres using an integral field spectrograph (IFS). In this paper, we report on the development of such an IFS for the High Contrast Imaging Lab (HCIL) at Princeton University, downstream of a Shaped Pupil coronagraph. Our final lensletbased design calls for the light in an 18% band around 660 nm to be dispersed with a spectral resolution of 50. We also present our new laboratory control software written in Python, allowing the import of open-source packages such as CRISPY to ultimately reconstruct 3D datacubes from IFS spatio-spectral science images. Finally, we show and discuss our preliminary first light results, reaching a contrast of ~10^-5 using in-house focal-plane wavefront control and estimation algorithms with two deformable mirrors.

We present designs for fully achromatic vector Apodizing Phase Plate (vAPP) coronagraphs, that implement low polarization leakage solutions and achromatic beam-splitting, enabling observations in broadband filters. The vAPP is a pupil plane optic, inducing the phase through the inherently achromatic geometric phase. We discuss various implementations of the broadband vAPP and set requirements on all the components of the broadband vAPP coronagraph to ensure that the leakage terms do not limit a raw contrast of 10^-5. Furthermore, we discuss superachromatic QWPs based of liquid crystals or quartz/MgF2 combinations, and several polarizer choices. As the implementation of the (broadband) vAPP coronagraph is fully based on polarization techniques, it can easily be extended to furnish polarimetry by adding another QWP before the coronagraph optic, which further enhances the contrast between the star and a polarized companion in reflected light. We outline several polarimetric vAPP system designs that could be easily implemented in existing instruments, e.g. SPHERE and SCExAO.

The Mid-infrared Imager, Spectrometer Coronagraph (MISC) instrument studied for the Origins Space Telescope (OST) Mission Concept 1 is designed to observe at mid-infrared (MIR) wavelengths ranging from 5 to 38 microns for OST. In the OST Mission Concept 1 study, MISC consists of three separate optical modules providing imaging, spectroscopy, and coronagraph capabilities. The MISC Coronagraph module (MISC COR) employs Phase-Induced Amplitude Apodization (PIAA) coronagraph (Guyon et al. 2014) in which pupil apodization is modified by reflection on mirrors and central starlight is blocked by focal plane mask and Lyot mask. The performance target of MISC COR is to achieve 10^-7 contrast at 0.5” from the central star with covering wavelength of 6-38 microns using 2 optical channels. MISC COR will be a powerful tool to bring a revolutionary progress in exoplanet sciences. In this paper, we present detailed design of its optics and optomechanics, and discuss expected performances for a variety of combination of focal plane mask and Lyot mask.

Phase-Induced Amplitude Apodization Complex Mask Coronagraphs (PIAACMC) offer high-contrast performance at a small inner-working angle (< 1 λ/D) with high planet throughput (> 70%). The complex mask is a multi-zone, phase-shifting mask comprised of tiled hexagons which vary in depth. Complex masks can be difficult to fabricate as there are many micron-scale hexagonal zones (> 500 on average) with continuous depths ranging over a few microns. Ensuring the broadband PIAACMC design performance carries through to fabricated devices requires that these complex masks are manufactured to within well-defined tolerances. We report on a simulated tolerance analysis of a "toy" PIAACMC design which characterizes the effect of common microfabrication errors on on-axis contrast performance using a simple Monte Carlo method. Moreover, the tolerance analysis provides crucial information for choosing a fabrication process which yields working devices while potentially reducing process complexity. The common fabrication errors investigated are zone depth discretization, zone depth errors, and edge artifacts between zones.

A new field re-configuration technique, Multiple Rooks of Chess, for multiple deployable Integral Field Spectrographs has been developed. The method involves a mechanical geometry as well as an optimized deployment algorithm. The geometry is found to be simple for mechanical implementation. The algorithm initially assigns the IFUs to the target objects and then devises the movement sequence based on the current and the desired IFU positions. The reconfiguration time using the suitable actuators which runs at 20 cm/s is found to be a maximum of 25 seconds for the circular DOTIFS focal plane (180 mm diameter). It is similar to some of the fastest schemes currently available. The Geometry Algorithm Combination (GAC) has been tested on several million mock target configurations with object-to-IFU ( τ ) ratio varying from 0.25 to 16. The configuration had both contiguous and sparse distribution of targets. The MRC method is found to be extremely efficient in target acquisition in terms of field revisit and deployment time without any collision or entanglement of the fiber bundles. The efficiency of the technique does not get affected by the increase of number density of target objects. For field with τ >1 prioritization of target objects is an optional feature and not necessary. The GAC can be modified for an instrument with higher or lower number of IFUs and different field size without any significant change in the flow. The technique is compared with other available methods based on sky coverage, flexibility and overhead time. The proposed geometry and algorithm combination is found to have advantage in all of the aspects.

Digital Micromirror Devices (DMDs), a type of Micro-Opto-ElectroMechanical System (MOEMS) device, are commonly used in Digital Light Processing (DLP) televisions and projectors. These devices consist of an array of hundreds of thousands to millions of micron-scale mirrors, each of which can be programmed to tilt in one of two directions. DMDs have proven useful in astronomy instrumentation where they have been used as a programmable slit, allowing light from a star or galaxy to be separated from the remainder of the field by tilting those mirrors aligned to the target toward the spectroscopic arm of the spectrograph, while the remaining mirrors are tilted to direct light to an imaging camera. When mirrors are tilted away from the spectroscopic arm, some light may still scatter back towards it, increasing the background noise. Characterizing this noise source is crucial to determining the sensitivity of the spectrograph. In this paper, we present contrast ratio measurement results for a Texas Instruments DLP7000. Two methods were used to determine the contrast ratio: 1) the ratio of the light intensity with all mirrors turned “on” to the intensity with all mirrors turned “off”; and 2), the ratio of the total number of mirrors illuminated compared to the number of mirrors required to reproduce the back-scattered light intensity. Additionally, we measured the ratio of the total light incident on the DMD surface compared to the total light back scattered to determine how much of the unwanted light entering the system becomes light scattered into the spectrograph. A variety of LEDs were used in the testing, ranging from 385 nm to 1050 nm. Both silicon and InGaAs photodiodes were used to measure the reflected light. In this work we present the details of the setup used to conduct the scattered light measurements, compare the two measurement methods, discuss the results of our testing, and provide analysis of the measured contrast.

This paper gives a scheme of optical fiber positioner structure of a miniature, by use of the DC servo motor with the diameter of 3mm driver, the distance can designed to 8.5mm, and can arrange more than 12000 fibers in the focal plane with the diameter of 1 meters, it is especially suitable for telescope with small dimension focal plane and has high density fiber positioning requirements. Based on the principle of double rotary fiber positioning principle, It consists of a hollow shaft revolving mechanism, and eccentric axis revolving mechanism relative to hollow shaft. The hollow shaft turns round at the range of -180 degrees to +180 degrees and the eccentric axis turns round at the range of -90 degrees to +90 degrees at the half of radius driving by each control motor. When positioning, the optical fiber end moves on the focal plate throughout, and can never deviate from focal plane. optical fiber is fixed in the mounting hole of fiber support which installed on the eccentric rotary shaft (fiber support’s hole axis is parallel to the axis of the hollow shaft), and fiber will lead to pass through the inner hole of the hollow shaft and focal plate then connected to the spectrometer. positioner center shaft adopts planetary gear driving principle, with small module motor’s gear and the fixed ring gear can driving motor and positioner planetary rotate, the eccentric shaft by DC servo motor with the diameter of 3mm drived coaxial optical fiber on the eccentric shaft, the center and the eccentric shafts adopts micro rolling bearing support; in order to prevent the positioner’s center and eccentric shaft to rotate out of bounds, both limiting devices have designed to ensure the safety of fiber positioning; both center and eccentric shaft are designed with a spring structure to eliminate the influence of gear clearance; because positioner size is very small, the positioner driving wire is embedded in the slot of the hollow shaft sleeve wall. This will not affect the fiber go through the center shaft’s holes and pass through the focal plane; positioner sample test results show that the closed-loop positioning can reached accuracy of 0.01mm unit, and can meet with the demand of optical fiber positioning.

The AAO Starbugs is a multi-functional positioning device used in the TAIPAN instrument currently being commissioned on the UK Schmidt Telescope at Siding Spring Observatory in Australia. TAIPAN is part of a design study for MANIFEST which is a fibre positioning instrument proposed for the Giant Magellan Telescope. The acquisition and guiding system for TAIPAN uses nine standard Starbugs, referred to as Guide Bugs. Each one uses a 7000 core coherent polymer fibre bundle on individual guide stars. This provides an astrometric reference frame for science fibre positioning, telescope guiding, instrument alignment and focus, all of which are invariant to telescope and atmospheric geometric anomalies. Guide Bugs are a technology that will enable improved science results for the TAIPAN instrument. In this paper we outline the design features and provide an update on software development.

Fiber spectroscopic telescopes are important tools for astronomy research. In spectroscopic telescopes, the positioning of thousands of fibers on the focal plane is a big issue, which is usually solved by some compact structured devices with small-size motors installed. Stepper motors are normal choice for fiber positioner, however, stepper motors’ low efficiency leads to serious heating, so brushless DC motor becomes a more possible option when the fiber positioner is required to be less heating. Moreover, the size of brushless motor is much smaller than stepper motor in same situation. Brushless DC motor are synchronous motors powered by DC electricity via an inverter. Brushless DC motors complete commutating by switching power supply with an inverter, instead of with the help of carbon brush. Because of the absence of Mechanical Structures like carbon brush and slip ring, BLDC Motors can prevent problems like friction that caused by carbon brush. Both brushless DC motors and Steppers are DC synchronous motors, they generally share the same mechanical structures, but they have many different features. Brushless DC motors perform well in acceleration and they are less likely to generate remarkable amount of noise or heat. Steppers is made for position control, but they sometimes step out, what’s more, they generate a lot of heat and noise while running. Brushless DC motors are usually used when high speed and small size are required, while Steppers are used for positioner. If we can use brushless DC motors for position control, in one way, we can solve the stepping out problem of Steppers and managed to achieve higher accuracy and performance control of position, in the other way, circumstances that need small size and low heat and position control, which may have bothered us a lot, may have an convenient economic solution by using BLDC Motors. Although BLDC Motors are not made for position control, but the Mechanical Structure similarity with Steppers make it possible to realize some kind of position control theoretically. By now, there many ways (with sensor and without sensor) to detect the position of the brushless DC motors’ rotor’s position, which make the idea of using BLDC Motors for position control possible in practice. Generally, ways with sensors detect the rotor position by placing a sensor in the motor, and those without sensors usually calculate the rotor position by detect the voltage and current of the motor. This paper presents our efforts in applying sensorless rotor positioning technology in driving the brushless DC motors and in using the method of sensorless positioning to realize position control. During the process of rotor position detection, a three-terminal resistance network of star arrangement and a simple RC filter is used to get the zero-crossing point of the back EMF. The resistance network is used to extract the neutral voltage and the filter can filter high-frequency background and direct current component. The filtered signal’s zero-crossing point is a shift of the back EMF’s zero-crossing point and almost can be directly used as a reference of the rotor position. Pulse-width-modulation is used to make it possible for the driver to adapt to different brushless motors and different torque. For the purpose of inspecting the performance of the technique when used in position control, the brushless DC motor is mounted to an optical fiber positioner to avoid no-load running and to verify the possibility of applying it for small positioner. The detailed control scheme is introduced, the circuit is analyzed and experimental results obtained form position control experiment are shown to estimate the accuracy of the motor. The result of this paper may help to simplify the control of brushless DC motor and improve the performance of brushless DC motor.

4MOST is a fibre-fed, multi-object spectroscopic survey facility to be installed on the VISTA telescope at ESO's Paranal observatory. This paper presents the final mechanical design of the optical fibre route from the fibre positioner at the focal plane of VISTA to the fibre-slits within the high- and low-resolution spectrographs below the azimuth platform. The technical challenges are to provide a safe, durable and efficient fibre route for over 2400 fibres. To accommodate the movements of the telescope, a Cassegrain Cable Wrap and a novel elevation chain concept has been prototyped and extensively tested to validate the design solutions.

The optical-fiber-based Integral Field Unit (IFU) is a very important device for astronomical observation. The IFU can obtain higher spatial resolution and good transmission efficiency. In this paper, a small IFU with 242 fibers was built for the prototype of the Fiber Arrayed Solar Optical Telescope (FASOT). It adopts the method of “micro lens + fiber array”. We designed the fiber with the core diameter of 35μm and NA 0.12. Two quartz positioning plates with micro pores were chosen to localize these fibers. And the micro lens was designed according to the parameter requirement. The coupling efficiency and the focal ratio between the micro lenses array and the fiber array are analyzed when position mismatch. The angular error is the main effect to influence the coupling efficiency.

The original optical fibre imaging bundles called `hexabundles' have proven to be exceptionally effective in the Sydney-AAO Multi-object IFS (SAMI) instrument, enabling one of the worlds largest IFS galaxy surveys^{5, 6}. We are now developing an improved next-generation hexabundle design. These IFUs use a novel assembly technique developed in the Sydney Astrophotonic Instrumentation Laboratories (SAIL) at the University of Sydney, that enable very high fill-fraction and an evenly distributed, hexagonally packed, array of 217 fibre cores. These new hexabundles will see first light in 2019 on the new Hector-I instrument for the Anglo-Australian Telescope (AAT). The large number of fibre cores will measure spatially-resolved spectroscopy of galaxies out to 2 effective radii. The hexabundles are currently being prototyped, and characterised. The impact of the hexagonal packing of the fibre cores on Focal Ratio Degradation (FRD), total throughput of the device and overall performance will be presented.

Modal noise has been shown to critically limit the signal-to-noise ratio achievable in fiber-coupled, high-resolution spectrographs. We are investigating new fiber technologies that can potentially solve the modal noise issues in the NIR region. The new technology that we present is a combination of a multicore fiber (MCF) and a photonic lantern (PL) specifically designed to provide highly efficient phase scrambling in the NIR with a low mode count. In this paper we give an overview of the specifications, design and manufacture of the multicore fiber and photonic lantern. We also present the initial modal noise test results for the MCF-PL and an octagonal multimode fiber for comparison.

The fiber positioner of LAMOST is used to realize the accurate positioning of optical fiber in the process of astronomical observation. However, the existence of various error sources can affect the position accuracy of the fiber, and cause the actual results cannot satisfy the requirement of precision. In this paper, a fiber positioner is taken as research object, and the sources of positioning error, including mechanism error and joint clearance, are taken into consideration. The corresponding error model is established based on Monte Carlo numerical simulation method and virtual prototyping technology respectively, and the impact of different error sources on positioning accuracy of fiber positioner is analyzed. The results show that when only considering mechanism error, the mean positioning error of the fiber positioner is small, which can satisfy the requirement of the observation accuracy. Furthermore, when the clearance between journal and bearing is considered, there is a deviation between fiber’s actual trajectory and ideal trajectory. With the increase of clearance, the deviation is becoming larger and larger making positioning accuracy of the fiber positioner worse even cannot meet the requirements of precision. The above analysis provides a theoretical basis for the design of a new generation of high precision fiber positioner in the future.

Major improvements to the SALT prime focus guidance system have been implemented over the last two years in the form of a new compact, modular and removable system with high optical efficiency. A double-probe positioning system allows both translation and rotation guidance, while optional beam-splitting allows closed-loop focus feedback to stabilise the focal plane. The features of this new system, its mechanical and optical performance and its control system architecture are presented.

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. We will describe the production and manufacturing processes developed for the 5000 fiber positioner robots mounted on the focal plane of the Mayall telescope.

This paper describes the design of an optical metrology system for fiber positioners. The system can be used for accurate calibration and verification of fiber positioners with SCARA-like RR planar kinematics. It is capable of measuring accurately the absolute position and tilt of the fiber tip over the whole workspace of the positioner. The metrology system works by back illuminating the optical fiber of the positioner with a laser. The position and tilt of the exiting cone at the tip of the fiber is measured with two optical cameras.

Microbends in multimode optical fibers are shown to lead to focal ratio degradation which compromises fiber fed spectrograph design and performance. By propagating specific vortex mode patterns through multimode fibers containing a single controlled microbend the mechanisms for FRD can be understood. For example, we see both experimentally and through ray tracing analysis that a microbend can produce spiral patterns in the far-field. These patterns are potentially useful tools for diagnosing termination problems in fiber assemblies. For example, by analyzing the spiral patterns produced by a single microbend it is possible to determine the location of a microbend hidden in the fiber termination.

White pupil arrangements using parabolic off-axis mirrors are commonly used by instrument designers of high-resolution spectrographs. Their advantage is a non-chromatic, spherical free collimation, an intermediate focus providing the possibility for stray light apertures, and the compression of the beam diameter using a second, a transfer, collimator. However, these arrangements suffer from off-axis aberrations in the field. Many configurations create the intermediate focus, after double-passing the primary collimator, in the vicinity of the spectrograph input. This makes it necessary to introduce small angles at the main collimator, further increasing off-axis aberrations. Furthermore, image curvature is high and requires toroidal surfaces to be added near the spectrograph focus in front of the CCD. In high-precision radial velocity measurements, it is of great importance to properly model the spectrographs transfer function in order to derive exact line positions. Therefore, clean and very well defined spots, even when working near the sampling limit, which can simply be represented by gaussians will benefit such measurements. This point is usually considered less by instrument designers. We have studied several possible off-axis mirror arrangements for white pupil spectrographs and discuss our results here. We focus on the image quality generated by the mirrors, on-axis as well as in the field. We come to the conclusion that a fairly uncommon arrangement provides best performance in the sense of image quality and focus accessibility.

We present a concept low-resolution spectrograph design for the Southern African Large Telescope (SALT) based on the O’Donoghue-Clemens Spherical Transmission Grating Spectrometer (STGS) principle. The design delivers R ~ 700 between 380 nm and 760 nm with a peak total efficiency estimated at 45%. This instrument type remains largely invariant with telescope size and can fit into a very compact volume (650 mm × 650 mm × 400 mm). This can truly be a new technology which may transform future instrument design — especially when matched to extremely large telescopes.

Here is presented the tests results and the lessons learnt concerning an opto-mechanical device to scan the GREGOR telescope field of view. The scanning is done by means of a set of mirrors and a mechanism which allows to keep the optical path length constant, regardless the portion of the field being scanned. This system is intended to feed a static image slicer used for solar observations. The tight level of tolerances required makes its design and tests a real challenging activity which produces a lot of unexpected lessons to learn. The story after the issues detection, the consequent root cause analysis, the additional tests and tools developed to study the phenomena, and the construction of the solutions and issue mitigation mechanisms provides a good background to elaborate some recommendations for future developments.

OCTOCAM is the new large Gemini instrument in building. It is an imaging spectrograph with 8 cameras covering the range 370 nm to 2350 nm at a typical resolution of 3000-4000. It will have 2 IFUs, one for normal operation over all wavelengths, the other for AO in the NIR only and with a smaller field but a higher spectral resolution. Currently, no IFU exists that covers the entire range of VIS and NIR in a single observation. Such an IFU would have a number of applications: It can be used for resolved studies of HII regions over a broad wavelength range and emission line galaxies over a broad redshift range using the same set of emission lines. Another application is to observe transients with only arcseconds localization very early without waiting for a sub-arcsecond position, hence allowing to obtain very valuable early data. For bright transients such as SNe and GRBs we can study the immediate environment in detail, and even use the actual transient as AO tip-tilt star to study the environment at high spectral and very high angular resolutions. The IFUs will be Advanced Image Slicers, a proven concept now in use in many instruments around the world including Gemini NIFS, VLT MUSE and KMOS, and JWST NIRSpec. The normal operation slicer will have a field of 9.7" x 6.8" with 17 slices 0.4" wide giving 0.18" x 0.4" spaxels. The slices are smaller than the standard slit size of 0.54" (3 pixels) so will deliver higher spectral resolution. This IFU will deliver much higher performances than the GMOS IFU and NIFS with a larger field of view and spectral range but also considerably fewer pixels per arsec² then reducing the readout noise. With its wavelength range starting at 370 nm, diamond machining cannot be used. A glass slicer system will have to be used as in MUSE. The wavelength range will however be much larger covering the whole VIS and NIR range. Modern reflection coatings as UV enhanced silver can be used but a trade-off may be better by starting at a longer wavelength to get higher transmission. Special consideration is necessary for the fore-optics which cannot be diamond machined and for the overall design due to the limited space envelope. The AO slicer will have a field of 2.5" x 3.6" with 31 slices 0.08" wide imaged on 2 pixels in the spectral direction to get proper sampling. The fore-optics will magnify the beam in both directions but with different magnifications to get spaxels of 0.08" x 0.08". The smaller slice image width will give a spectral resolution of about 5000 including aberrations, about the same than NIFS but covering all 4 NIR bands at once. This slicer uses a slit 60% longer than OCTOCAM is designed for. It is possible because the magnification reduces the beam size so the aberrations and vignetting.

We investigated the geometrical characteristics of off-axis parabolic mirrors (OPMs). We found that the clear aperture of an OPM is an ellipse with a set of major/minor diameters, and the center of the elliptical aperture does not correspond to the deepest depth of the mirror. Despite this property, the distance from the reference optical axis (ROA) of the parent parabolic mirror to the deepest point of the OPM is equal to the distance from the ROA to the center of the elliptical aperture of the OPM. This enables one to define an OPM by projecting a aperture perpendicular to the ROA on a parabolic surface.

We demonstrate the direct inscription of aperiodic fiber Bragg gratings (AFBGs) for their use as in-fiber filter elements. The modifications are induced by focusing ultrashort laser pulses with an oil-immersion objective into the fiber core. We apply an advanced point-by-point inscription technique for flexible period adaptation. The fabricated AFBGs are targeted on the suppression of 10 lines in a single grating and simulations based on the specific design show excellent agreement. Furthermore, we discuss the application in astronomy as filters for the suppression of OH emission lines.

With the completion of the full 50 m primary reflector surface of the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT/GTM), the project also upgraded the primary surface actuators. These actuators were custom-designed by ADS International in Valmadrera, Italy to meet the accuracy, load, and physical size requirements necessary for robust operation. Specifically, the actuators had to provide precise and repeatable positioning, support both operational and survival loading conditions for even the largest surface segments, and still fit within the geometric constraints imposed by interior angles of the backup structure truss members. Factory and laboratory testing confirmed that the actuators should meet the requirements. As reported in earlier papers, the LMT/GTM site poses particular challenges for electromechanical devices. As expected for a mountaintop site (4,600 m), the low atmospheric density reduces cooling effectiveness for motors and drives. To add to the challenge, the ambient temperature hovers near freezing and there is significant precipitation during the summer. This results in frequent freeze/thaw cycles. The constant formation and either sublimation or melting of ice has been an operational challenge for many devices at the LMT/GTM. Because of the large number of primary surface actuators (720 in total), it is particularly important that these units, their drive control boxes, and their cable connections be able to meet all specifications even under the site conditions. To confirm the suitability of the actuators, the LMT/GTM procured an initial set of sixteen actuators for testing at the site. After laboratory testing, the actuators were installed into the outer two rings of the telescope and cycled from February 2016 through January 2017. This extended testing provided direct operational experience over a wide variety of weather conditions. The program was long enough to provide confidence in the actuator design. With the first article testing complete, the project ordered a production run of the actuators. The installation of these actuators met the telescope completion plan requirement of bringing the LMT/GTM to a 50 m active surface telescope for the 2017-18 scientific observing season. This paper presents the final report on the first article testing program, as well as a summary of the characterized performance of the production actuators prior to installation.

The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of 156 identical spectrographs fed by 35,000 fibers from the upgraded 10-meter Hobby-Eberly Telescope (HET). VIRUS is in a phased deployment. At the submission of this paper, over half of the units are installed and the full support infrastructure is operational. This paper will describe the VIRUS infrastructure which includes the physical support system, the air cooling, the cryogenic cooling, and the temperature control of VIRUS. The paper will also discuss the various installation, maintenance, and operational procedures based on growing experience with the VIRUS array.