This PDF file contains the front matter associated with SPIE Proceedings Volume 10708, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

POLARBEAR-2 is a new receiver system, which will be deployed on the Simons Array telescope platform, for the measurement of Cosmic Microwave Background (CMB) polarization. The science goals with POLARBEAR-2 are to characterize the B-mode signal both at degree and sub-degree angular-scales. The degree-scale polarization data can be used for quantitative studies on inflation, such as the reconstruction of the energy scale of inflation. The sub-degree polarization data is an excellent tracer of large-scale structure in the universe, and will lead to precise constraints on the sum of the neutrino masses. In order to achieve these goals, POLARBEAR-2 employs 7588 polarization-sensitive antenna-coupled transition-edge sensor (TES) bolometers on the focal plane cooled to 0.27K with a three-stage Helium sorption refrigerator, which is ~6 times larger array over the current receiver system. The large TES bolometer array is read-out by an upgraded digital frequency-domain multiplexing system capable of multiplexing 40 bolometers through a single superconducting quantum interference device (SQUID). The first POLARBEAR-2 receiver, POLARBEAR-2A is constructed and the end-to-end testing to evaluate the integrated performance of detector, readout, and optics system is being conducted in the laboratory with various types of test equipments. The POLARBEAR-2A is scheduled to be deployed in 2018 at the Atacama desert in Chile. To further increase measurement sensitivity, two more POLARBEAR-2 type receivers will be deployed soon after the deployment (Simons Array project). The Simons Array will cover four frequency bands at 95GHz, 150GHz, 220GH and 270GHz for better control of the foreground signal. The projected constraints on a tensor-to-scalar ratio (amplitude of inflationary B-mode signal) is σ(r=0.1) = $6.0 \times 10^{-3}$ after foreground removal ($4.0 \times 10^{-3}$ (stat.)), and the sensitivity to the sum of the neutrino masses when combined with DESI spectroscopic galaxy survey data is 40 meV at 1-sigma after foreground removal (19 meV(stat.)). We will present an overview of the design, assembly and status of the laboratory testing of the POLARBEAR-2A receiver system as well as the Simons Array project overview.

The South Pole Telescope (SPT) is a millimeter-wavelength telescope designed for high-precision measurements of the cosmic microwave background (CMB). The SPT measures both the temperature and polarization of the CMB with a large aperture, resulting in high resolution maps sensitive to signals across a wide range of angular scales on the sky. With these data, the SPT has the potential to make a broad range of cosmological measurements. These include constraining the effect of massive neutrinos on large-scale structure formation as well as cleaning galactic and cosmological foregrounds from CMB polarization data in future searches for inflationary gravitational waves. The SPT began observing in January 2017 with a new receiver (SPT-3G) containing ~16,000 polarization-sensitive transition-edge sensor bolometers. Several key technology developments have enabled this large-format focal plane, including advances in detectors, readout electronics, and large millimeter-wavelength optics. We discuss the implementation of these technologies in the SPT-3G receiver as well as the challenges they presented. In late 2017 the implementations of all three of these technologies were modified to optimize total performance. Here, we present the current instrument status of the SPT-3G receiver.

The Simons Observatory (SO) will make precision temperature and polarization measurements of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales between 1 arcminute and tens of degrees, contain over 40,000 detectors, and sample frequencies between 27 and 270 GHz. SO will consist of a six-meter-aperture telescope coupled to over 20,000 detectors along with an array of half-meter aperture refractive cameras, coupled to an additional 20,000+ detectors. The unique combination of large and small apertures in a single CMB observatory, which will be located in the Atacama Desert at an altitude of 5190 m, will allow us to sample a wide range of angular scales over a common survey area. SO will measure fundamental cosmological parameters of our universe, find high redshift clusters via the Sunyaev-Zeldovich effect, constrain properties of neutrinos, and seek signatures of dark matter through gravitational lensing. The complex set of technical and science requirements for this experiment has led to innovative instrumentation solutions which we will discuss. The large aperture telescope will couple to a cryogenic receiver that is 2.4 m in diameter and over 2 m long, creating a number of interesting technical challenges. Concurrently, we are designing an array of half-meter-aperture cryogenic cameras which also have compelling design challenges. We will give an overview of the drivers for and designs of the SO telescopes and the cryogenic cameras that will house the cold optical components and detector arrays.

BFORE is a high-altitude ultra-long-duration balloon mission to map the cosmic microwave background (CMB). During a 28-day mid-latitude ight launched from Wanaka, New Zealand, the instrument will map half the sky to improve measurements of the optical depth to reionization tau. This will break parameter degeneracies needed to detect neutrino mass. BFORE will also hunt for the gravitational wave B-mode signal, and map Galactic dust foregrounds. The mission will be the first near-space use of TES/mSQUID multichroic detectors (150/217 GHz and 280/353 GHz bands) with low-power readout electronics.

The Primordial Inflation Polarization ExploreR (PIPER) is a balloon-borne instrument optimized to measure the polarization of the CMB at large angular scales. It will map 85% of the sky over a series of conventional balloon flights from the Northern and Southern hemispheres, measuring the B-mode polarization power spectrum over a range of multipoles from 2-300 covering both the reionization bump and the recombination peak, with sensitivity to measure the tensor-to-scalar ratio down to r = 0.007. PIPER will observe in four frequency bands centered at 200, 270, 350, and 600 GHz to characterize dust foregrounds. The instrument has background-limited sensitivity provided by fully cryogenic (1.7 K) optics focusing the sky signal onto kilo-pixel arrays of time-domain multiplexed Transition-Edge Sensor (TES) bolometers held at 100 mK. Polarization sensitivity and systematic control are provided by front-end Variable-delay Polarization Modulators (VPMs). PIPER had its engineering ight in October 2017 from Fort Sumner, New Mexico. This papers outlines the major components in the PIPER system discussing the conceptual design as well as specific choices made for PIPER. We also report on the results of the engineering flight, looking at the functionality of the payload systems, particularly VPM, as well as pointing out areas of improvement.

Bicep Array is the newest multi-frequency instrument in the Bicep/Keck Array program. It is comprised of four 550mm aperture refractive telescopes observing the polarization of the cosmic microwave background (CMB) at 30/40, 95, 150 and 220/270 GHz with over 30,000 detectors. We present an overview of the receiver, detailing the optics, thermal, mechanical, and magnetic shielding design. Bicep Array follows Bicep3's modular focal plane concept, and upgrades to 6" wafer to reduce fabrication with higher detector count per module. The first receiver at 30/40GHz is expected to start observing at the South Pole during the 2019-20 season. By the end of the planned Bicep Array program, we project 0.002 ⪅ σ(r) ⪅ 0.006, assuming current modeling of polarized Galactic foreground and depending on the level of delensing that can be achieved with higher resolution maps from the South Pole Telescope.

POLARBEAR is a cosmic microwave background (CMB) polarization experiment located in the Atacama desert in Chile. The science goals of the POLARBEAR project are to do a deep search for CMB B-mode polarization created by inflationary gravitational waves, as well as characterize the CMB B-mode signal from gravitational lensing. POLARBEAR-1 started observations in 2012, and the POLARBEAR team has published a series of results from its first two seasons of observations, including the first measurement of a non-zero B-mode polarization angular power spectrum, measured at sub-degree scales where the dominant signal is gravitational lensing of the CMB. The Simons Array expands POLARBEAR to include an additional two telescopes with next-generation POLARBEAR-2 multi-chroic receivers, observing at 95, 150, 220, and 270 GHz. The POLARBEAR-2A focal plane has 7,588 transition-edge sensor bolometers, read out with frequency-division multiplexing, with 40 frequency channels within the readout bandwidth of 1.5 to 4.5 MHz. The frequency channels are defined by a low-loss lithographed aluminum spiral inductor and interdigitated capacitor in series with each bolometer, creating a resonant frequency for each channel's unique voltage bias and current readout. Characterization of the readout includes measuring resonant peak locations and heights and fitting to a circuit model both above and below the bolometer superconducting transition temperature. This information is used determine the optimal detector bias frequencies and characterize stray impedances which may affect bolometer operation and stability. The detector electrical characterization includes measurements of the transition properties by sweeping in temperature and in voltage bias, measurements of the bolometer saturation power, as well as measuring and removing any biases introduced by the readout circuit. We present results from the characterization, tuning, and operation of the fully integrated focal plane and readout for the first POLARBEAR-2 receiver, POLARBEAR-2A, during its pre-deployment integration run.

We are developing Thermal Kinetic Inductance Detector (TKID) bolometers for submillimter astronomy and CMB polarimetry with the BICEP Array's 250GHz dust monitor camera as an early application. We couple power to our bolometers by resistive terminations to antenna-fed microstrip circuits and sense changes in temperature with a membrane isolated microwave kinetic inductance thermometer (MKIT). The MKIT resonates with an off-island capacitor and capacitively couples to a microstrip transmission line to provide radio-frequency multiplexing analogous to that of traditional non-phonon-mediated KIDs. By splitting the absorption, sensing, and relaxation of quasiparticles back to the thermal bath into different sub-devices, we attain more design degrees of freedom than KIDs and can tailor the detector’s performance. We will report on the design and performance of our optically coupled TKIDs and comment on the sensitivity, emphasizing TLS and vibrational noise mechanisms. We will also show preliminary results from studies of the detectors optical properties as defined by the antenna-array the coupled power to the detector. Lastly, we will describe designs for a 900 detector pathfinder camera that will precede the full 20,000 BICEP Array camera.

The Advanced Atacama Cosmology Telescope Polarimeter (AdvACT) is an upgraded instrument for the Atacama Cosmology Telescope, which uses transition-edge sensor (TES) detector arrays to measure cosmic microwave background (CMB) polarization anisotropies in multiple frequency bands. We review the integration and characterization of the final polarimeter array, which is the low frequency (LF) array, consisting of 292 TES bolometers observing in two bands centered at 27 GHz and 39 GHz. This array is sensitive to synchrotron radiation from our galaxy as well as to the CMB, and complements the AdvACT arrays operating at 90, 150 and 230 GHz to provide robust detection and removal of foreground contamination. We present detector parameters for the LF array measured in the lab, including saturation powers, critical temperatures, thermal conductivities, time constants and optical efficiencies, and their uniformity across the entire wafer.

EBEX-IDS is a balloon-borne polarimeter designed to characterize the polarization of foregrounds and to detect the primordial gravity waves through their B-mode signature on the polarization of the cosmic microwave background (CMB). EBEX-IDS will operate 20,562 transition edge sensor (TES) bolometers distributed among 3,427 polarization sensitive sinuous antenna multichroic pixels (SAMP) to observe the CMB in 7 frequency bands between 150 and 360 GHz. In order to maximize the sensitivity of the telescope and take advantage of the lower power emission and absorption of the atmosphere at float, we decrease the average thermal conductance of the bolometers by a factor of 10 compared to ground-based telescopes and observe within higher frequency bands. We use a meandered design with thinner legs to reduce the thermal conductance. We present prototype pixels which improve the technology readiness for the use of SAMPs in balloon and satellite platforms. We fabricated and tested 150/250/320, 180/250/320 and 220/280/350 GHz SAMPs suitable for EBEX-IDS with specified average thermal conductance of 9 pW/K designed to absorb as little as 0.2 pW at 150 GHz. We report on the characterization of the average thermal conductance, the critical temperature and the time-constant of these pixels as well as the measurement of their noise and optical properties. We also report on the fabrication and testing of a new inductor-capacitor chip operated at 4 K to read out up to 105 bolometers with two wires using the frequency domain multiplexing ICE readout boards. This factor represents an increase of 60% compared to the highest factor used to date with this readout system.

We present novel optics solutions based on metal mesh flat lenses which can be used to mimic a refracting lens. This approach removes the bulk of the dielectric materials (polyethylene or silicon) required for fast optical refracting systems. Additional attractive property of these lenses is that they filter out unwanted higher frequency radiation, they are easy to anti-reflection coat and they are extremely light. Measurements from 300mm diameter prototypes of both a Fresnel-type graded-index lens and a phase-delay type mesh-lens are presented.

We present our design and development of a polarization modulator unit (PMU) for LiteBIRD space mission. LiteBIRD is a next generation cosmic microwave background (CMB) polarization satellite to measure the primordial B-mode. The science goal of LiteBIRD is to measure the tensor-to-scalar ratio with the sensitivity of δr < 10^-3. The baseline design of LiteBIRD is to employ the PMU based on a continuous rotating half-wave plate (HWP) at a telescope aperture with a diameter of 400 mm. It is an essential for LiteBIRD to achieve the science goal because it significantly reduces detector noise and systematic uncertainties. The LiteBIRD PMU consists of a multi-layered sapphire as a broadband achromatic HWP and a mechanism to continuously rotate it at 88 rpm. The whole system is maintained at below 10K to minimize the thermal emission from the HWP. In this paper, we discuss the current development status of the broadband achromatic HWP and the cryogenic rotation mechanism.

We present the design and performance of broadband and tunable infrared-blocking filters for millimeter and sub-millimeter astronomy composed of small scattering particles embedded in an aerogel substrate. The ultralow-density (< 100 mg/cm³) aerogel substrate provides an index of refraction as low as 1.05, removing the need for anti-reflection coatings and allowing for broadband operation from DC to above 1 THz. The size distribution of the scattering particles can be tuned to provide a variable cutoff frequency. Aerogel filters with embedded high-resistivity silicon powder are being produced at 40-cm diameter to enable large-aperture cryogenic receivers for cosmic microwave background polarimeters, which require large arrays of sub-Kelvin detectors in their search for the signature of an inflationary gravitational-wave background.

Using the long-established Cardiff metal-mesh filter technology, we have exploited our ability to artificially manipulate the phase of a wavefront across a device in order to produce a dielectric-based Toraldo pupil working at millimeter wavelengths. The use of a Toraldo pupil to push the angular resolution of an optical imaging system beyond the classical diffraction limit is yet to be realized in the millimeter regime, but is an exciting prospect. Here we present the design and measured performance of a prototype Toraldo pupil, based on a 5 annuli design.

The need for larger arrays of millimeter and submillimeter wavelength detectors for Cosmic Microwave Background (CMB) experiments is driving a demand for focal planes which can field large numbers of detectors with both high sensitivity and wide bandwidth. Current CMB experiments have $\sim 10^{4}$ detectors, with next generation focal planes requiring $\sim 10^{5}$ or more. One challenge of expanding the array size is coupling the detectors to instrument optics with a method that is broadband, low loss, and scalable. Current state of the art methods of coupling incident radiation include phased array antenna-coupled detectors, corrugated feedhorn arrays, and hemispherical lenslet array-coupled planar antennas. Phased array antennas are fabricated using planar lithography techniques and therefore easily scalable, but are typically narrow band ($\sim 30\%$). Silicon platelet feedhorns are scalable and low loss, but typically achieve only an octave of bandwidth. Lenslets have been produced using silicon hemispheres stacked on silicon plates to approximate an elliptical lens. Low loss and broadband behavior is accomplished by individually molding anti-reflection layers made of materials with appropriate refractive indices and individually glued to arrays; however this approach does not easily scale to larger arrays. We are developing planar lenslet arrays using metamaterials fabricated with standard microlithograpy techniques on silicon wafers. Instead of using difficult to manufacture curved optical surfaces, the lenslets consist of stacks of silicon wafers which are each patterned with an array of sub-wavelength features to produce optical features which form a well defined beam at measurement wavelengths. These arrays are being developed using two approaches: GRadient INdex (GRIN) lenslets which are fabricated by etching holes on a sub-wavelength grid to produce a spatially varying effective index of refraction, and metal-mesh lenslets which are produced by depositing spatially varying metallic features which act as a series of Transmission Line (TL) lumped element features to control phase delay across the wafer. GRIN lenslets are fabricated by etching sub-wavelength holes on a periodic, sub-wavelength grid using standard microlithography techniques. The wafers can be stacked, allowing the spatial index to be altered along all dimensions, which allows for arbitrary anti-reflective coatings to be integrated in the lenslet design. Simulations in finite element modeling (FEM) software have been used to both evaluate the effective index of an individual element and simulate full lenslet structures. Dielectrically embedded mesh-lenses are based on existing mesh-filter technology. Differently from the mesh-filters, the grids are inhomogeneous and their geometry is designed in such a way to impart variable phase shifts across the surface. The local phase shifts reproduce those that would be introduced by a classical dielectric lens. In this work we are developing mesh-lenslets on silicon substrates. The metal grids are supported by silicon nitride (SiN) membranes and kept at specific distances in an air-gap configuration. Finite element analysis is used to quantify and optimize the performance of these devices. We report on progress in both lenslet design approaches. In each case we have developed a set of design equations which guide the design of the full lenslet structure. These structures are simulated using finite element modeling simulations. We report on measurements and efficacy of the design and simulation process and agreement with laboratory measurements of prototype lenslet arrays.

The mm-wavelength sky reveals the initial phase of structure formation, at all spatial scales, over the entire observable history of the Universe. Over the past 20 years, advances in mm-wavelength detectors and camera systems have allowed the field to take enormous strides forward – particularly in the study of the Cosmic Microwave Background – but limitations in mapping speeds, sensitivity and resolution have plagued studies of astrophysical phenomena. In fact, limitations due to inherent biases in the ground-based mm-wavelength surveys conducted over the last 2 decades continue to motivate the need for deeper and wider-area maps made with increased angular resolution. TolTEC is a new camera that will fill the focal plane of the 50m diameter Large Millimeter Telescope (LMT) and provide simultaneous, polarization-sensitive imaging at 2.0, 1.4, and 1.1mm wavelengths. The instrument, now under construction, is a cryogenically cooled receiver housing three separate kilo-pixel arrays of Kinetic Inductance Detectors (KIDs) that are coupled to the telescope through a series of silicon lenses and dichroic splitters. TolTEC will be installed and commissioned on the LMT in early 2019 where it will become both a facility instrument and also perform a series of 100 hour “Legacy Surveys” whose data will be publicly available. The initial four surveys in this series: the Clouds to Cores Legacy Survey, the Fields in Filaments Legacy Survey, the Ultra-Deep Legacy Survey and the Large Scale Structure Survey are currently being defined in public working groups of astronomers coordinated by TolTEC Science Team members. Data collection for these surveys will begin in late 2019 with data releases planned for late 2020 and 2021. Herein we describe the instrument concept, provide performance data for key subsystems, and provide an overview of the science, schedule and plans for the initial four Legacy Survey concepts.

TolTEC is a new camera being built for the 50-meter Large Millimeter-wave Telescope (LMT) in Puebla, Mexico to survey distant galaxies and star-forming regions in the Milky Way. The optical design simultaneously couples the field of view onto focal planes at 150, 220, and 280 GHz. The optical design and detector properties, as well as a data-driven model of the atmospheric emission of the LMT site, inform the sensitivity model of the integrated instrument. This model is used to optimize the instrument design, and to calculate the mapping speed as an early forecast of the science reach of the instrument.

We give an overview of the baseline detector system for SAFARI, the prime focal-plane instrument on board the proposed space infrared observatory, SPICA. SAFARI's detectors are based on superconducting Transition Edge Sensors (TES) to provide the extreme sensitivity (dark NEP≤2×10^-19 W/√Hz) needed to take advantage of SPICA's cold (<8 K) telescope. In order to read out the total of ~3500 detectors we use frequency domain multiplexing (FDM) with baseband feedback. In each multiplexing channel, a two-stage SQUID preamplifier reads out 160 detectors. We describe the detector system and discuss some of the considerations that informed its design.

The Next Generation Balloon-borne Large Aperture Submillimeter Telescope (BLAST-TNG) is a submillimeter mapping experiment planned for a 28 day long-duration balloon (LDB) flight from McMurdo Station, Antarctica during the 2018-2019 season. BLAST-TNG will detect submillimeter polarized interstellar dust emission, tracing magnetic fields in galactic molecular clouds. BLAST-TNG will be the first polarimeter with the sensitivity and resolution to probe the ~0.1 parsec-scale features that are critical to understanding the origin of structures in the interstellar medium.

BLAST-TNG features three detector arrays operating at wavelengths of 250, 350, and 500 m (1200, 857, and 600 GHz) comprised of 918, 469, and 272 dual-polarization pixels, respectively. Each pixel is made up of two crossed microwave kinetic inductance detectors (MKIDs). These arrays are cooled to 275 mK in a cryogenic receiver. Each MKID has a different resonant frequency, allowing hundreds of resonators to be read out on a single transmission line. This inherent ability to be frequency-domain multiplexed simplifies the cryogenic readout hardware, but requires careful optical testing to map out the physical location of each resonator on the focal plane. Receiver-level optical testing was carried out using both a cryogenic source mounted to a movable xy-stage with a shutter, and a beam-filling, heated blackbody source able to provide a 10-50 C temperature chop. The focal plane array noise properties, responsivity, polarization efficiency, instrumental polarization were measured. We present the preflight characterization of the BLAST-TNG cryogenic system and array-level optical testing of the MKID detector arrays in the flight receiver.

The Mexico-UK Sub-millimetre Camera for AsTronomy (MUSCAT) is a large-format, millimetre-wave camera consisting of 1,500 background-limited lumped-element kinetic inductance detectors (LEKIDs) scheduled for deployment on the Large Millimeter Telescope (Volcán Sierra Negra, Mexico) in 2018. MUSCAT is designed for observing at 1.1 mm and will utilise the full 40 field of view of the LMTs upgraded 50-m primary mirror. In its primary role, MUSCAT is designed for high-resolution follow-up surveys of both galactic and extra-galactic sub-mm sources identified by Herschel. MUSCAT is also designed to be a technology demonstrator will provide the first on-sky demonstrations of novel design concepts such as horn-coupled LEKID arrays and closed continuous cycle miniature dilution refrigeration.

Here we describe some of the key design elements of the MUSCAT instrument such as the novel use of continuous sorption refrigerators and a miniature dilutor for continuous 100-mK cooling of the focal plane, broadband optical coupling to Aluminium LEKID arrays using waveguide chokes and anti-reflection coating materials as well as with the general mechanical and optical design of MUSCAT. We will explain how MUSCAT is designed to be simple to upgrade and the possibilities for changing the focal plane unit that allows MUSCAT to act as a demonstrator for other novel technologies such as multi-chroic polarisation sensitive pixels and on-chip spectrometry in the future. Finally, we will report on the current status of MUSCAT's commissioning.

An ultra-wideband, large field-of-view (sub)millimeter wave imaging spectrometer is imperative for uncovering the evolution of dust-enshrouded cosmic star formation rate, galaxy evolution, and structure formation, over cosmic time. Here we report the first on-sky demonstration of DESHIMA. DESHIMA (Deep Spectroscopic High-redshift Mapper) is a new type of submillimeter wave spectrometer, which uses a superconducting filterbank on a chip to achieve a very wide instantaneous bandwidth. Compared to an optical spectrometer with equivalent performance, such an on-chip spectrometer is not only compact, but also offers a higher degree of potential scalability to multiple spatial pixels. On the filterbank spectrometer chip of DESHIMA, the signal captured by the lens-antenna travels through a coplanar waveguide made of superconducting NbTiN, from which planar NbTiN bandpass filters branch out to divide the signal into frequency channels. At the output of each filter is a NbTiN/Al hybrid kinetic inductance detector (KID). These KIDs are operated at 120 mK with a 2-stage adiabatic demagnetization refrigerator (ADR), and their response is read out using the SpaceKIDs readout electronics. Being in its phase-1 configuration, DESHIMA currently covers the 330-370 GHz band with 49 spectral channels, offering a spectral resolution F/dF = 400, or dV = 700 km/s. This design is intended as a scalable prototype towards the phase-2 DESHIMA instrument, which targets at 240-720 GHz instantaneous band coverage with a resolution of F/dF = 500 (dV = 600 km/s), and >2 spatial pixels. In the laboratory, the sensitivity and frequency response of DESHIMA was characterized using a black-body calibration source and a THz photo-mixer source, respectively. The sensitivity is photon-noise limited at a detector loading power of ~1 pW, with a photon-noise limited optical Noise Equivalent Power of 1-2 x 10^-16 W Hz^-0.5. From October to November 2017, DESHIMA was installed on the Atacama Submillimeter Telescope Experiment (ASTE), a 10 m diameter antenna in the Atacama Desert of Chile. The sensitivity of DESHIMA measured inside the ASTE cabin is similar to lab results. At the time of submission of the abstract, DESHIMA has successfully detected multiple astronomical sources, in both continuum and line emission. At the conference we will report the lessons learned in the first actual operation of an on-chip filterbank spectrometer on a telescope, including the influence of thermal cycles on the filters, system susceptibility to telescope environment and motion, on-sky beam pattern, and sensitivity to continuum and line emission.

We will present a status update on the development of HIRMES, the third generation instrument for SOFIA (Stratospheric Observatory for Infrared Astronomy). HIRMES (HIgh Resolution Mid-infrarEd Spectrometer) will cover the wavelength range between 25 micron and 122 micron with a spectral resolution of up to R~100,000. It will use two arrays of Transition Edge Sensed (TES) bolometers. One of the arrays consists of 8 16-pixel strips, for the high-resolution mode, where the pixel area and backshorts are optimized for 8 different wavelength regimes. The second detector consists of a 16x64 array with excellent sensitivity over the full wavelength range, and it will be used for the mid-resolution (R~19,000) and low-resolution (R~2,000 and R~600) observing modes. Both detector arrays will have background limited performance with NEPs of < 2E-17 W/Hz^(1/2) for the low-resolution array and < 3E-18 W/Hz^(1/2) for the high-resolution array. HIRMES will employ several Fabry-Perot Interferometers (FPI) for the low- (R~2000), mid- (R~19,000), and high-resolution (R~100,000) observing modes. In addition, three gratings with resolutions of R~600 will be used to order-sort FPI transmission peaks, and also to obtain low resolution broad bandwidth spectra. HIRMES's main science goals are to study the evolution of protoplanetary disks as well as to investigate the origin of Hydrogen and Deuterium in the Solar System. The high spectral resolution observations of the HD 1-0 R(0) line at 112 micron will determine the gas mass and kinematics in protoplanetary disks, while the observations of the [OI] 63 micron and H2O lines reveal the amount of Oxygen and H20 within the snowline. Low spectral resolution observations of solid-state H20 ice features at ~43 and ~63 micron will determine the amount of water ice beyond the snowline. Measurements of the molecular hydrogen line and numerous HD lines at mid-resolution will help to estimate the H/D ratio in the Solar System. In addition, the low-resolution FPI is well suited to map fine-structure line emission from nearby galaxies.

SuperSpec is a new technology for millimeter and submillimeter spectroscopy. It is an on-chip spectrometer being developed for multi-object, moderate resolution (R = ~300), large bandwidth survey spectroscopy of high-redshift galaxies for the 1 mm atmospheric window. SuperSpec targets the CO ladder in the redshift range of z = 0 to 4, the [CII] 158 um line from z = 5 to 9, and the [NII] 205 um line from z = 4-7. All together these lines offer complete redshift coverage from z = 0 to 9. SuperSpec employs a novel architecture in which detectors are coupled to a series of resonant filters along a single microwave feedline instead of using dispersive optics. This construction allows for the creation of a full spectrometer occupying only 20 cm squared of silicon, a reduction in size of several orders of magnitude when compared to standard grating spectrometers. This small profile enables the production of future multi-object spectroscopic instruments required as the millimeter-wave spectroscopy field matures. SuperSpec uses a lens-coupled antenna to deliver astrophysical radiation to a microstrip transmission line. The radiation then propagates down this transmission line where upon proximity coupled half wavelength microstrip resonators pick off specific frequencies of radiation. Careful tuning of the proximity of the resonators to the feedline dials in the desired resolving power of the SuperSpec filterbank by tuning the coupling quality factor. The half wavelength resonators are then in turn coupled to the inductive meander of kinetic inductance detectors (KIDs), which serve as the power detectors for the SuperSpec filterbank. Each SuperSpec filter bank contains hundreds of titanium nitride TiN KIDs and the natural multiplexibility of these detectors allow for readout of the large numbers of required detectors. The unique coupling scheme employed by SuperSpec allows for the creation of incredibly low volume (2.6 cubic microns), high responsivity, TiN KIDs. Since responsivity is proportional to the inverse of quasiparticle-occupied volume, this allows SuperSpec to reach the low NEPs required by moderate resolution spectroscopy to be photon limited from the best ground-based observing sites. We will present the latest results from SuperSpec devices. In particular, detector NEPs, measured filter bank efficiency (including transmission line losses), and spectral profiles for a full ~ 300-channel filterbank. Finally, we will report on our system end to end efficiency and total system NEP.

Photon-counting detectors address the single most difficult technology challenge for the Origins Space Telescope (OST) and are highly desirable for reaching the ~ 10^-20 W/√Hz sensitivity permitted by the observatory. One objective of this facility is rapid spectroscopic surveys of the high redshift universe at 420 – 800 μm, using arrays of integrated spectrometers with moderate resolutions (R = λ/Δλ ~1000), to explore galaxy evolution and growth of structure in the universe. A second objective is to perform higher resolution (R > 100,000) spectroscopic surveys at 20–300 μm for exploring the distribution of the ingredients for life in protoplanetary disks. Lastly, the OST aims to do sensitive mid-infrared (5–30 μm) spectroscopy of rocky planet atmospheres in the habitable zone using the transit method. These objectives represent a well-organized community agreement, but they are impossible to reach without a significant leap forward in detector technology, and the OST is likely not to be recommended if a path to suitable detectors does not exist. Our team is developing photon-counting Kinetic Inductance Detectors (KIDs) for the OST. Since KIDs are highly multiplexable in nature their scalability will be a major improvement over current technologies that are severely limited in observing speed due to small numbers of pixels. Moreover, KIDs are an established strong competitor to TESs and have achieved NEP ~ 1.5—3x10^-19 W/√Hz in a fully operational 1000-pixel science grade array made by SRON under the SpaceKID program. To reach the sensitivities for OST we are developing KIDs made from very thin aluminum films on single-crystal silicon substrates. Under the right conditions, small-volume inductors made from these films can become ultra-sensitive to single photons >90 GHz. Understanding the material physics and electrodynamics of excitations in these superconductor-dielectric systems is critical to performance. We have achieved world-record material properties, which are within requirements for photon-counting: microwave quality factor of 0.5 x 10^6 for a 10-nm aluminum resonator at single microwave photon drive power, residual dark electron density of < 5 /µm^3 and extremely long excitation lifetime of ~ 6.0 ms. Using a detailed model we simulated our detector when illuminated with randomly arriving single photon events and show that photon counting with >95% efficiency at 0.5 - 1.0 THz is achievable. Combined with µ-Spec - our Goddard-based on-chip far-IR spectrometer - these detectors will enable the first OST science objective mentioned above, and provide a clear path for the shorter wavelength objectives as well.

Future space based observatories for the far infrared and sub-millimeter, such as SPICA and the origins space telescope (OST), will need ultra-sensitive background limited detectors at frequencies above 1 THz. We have developed a kinetic inductance detector (KID) coupled to dual polarization, broad band antenna. The detector combines high optical efficiency in two polarizations and broad band radiation detection from 1.4 to 2.8 THz. The detector consists of a hybrid niobium titanium nitride/aluminum (NbTiN/Al) Kinetic Inductance Detector, fabricated on a silicon (Si) substrate. Radiation coupling is achieved using a so-called leaky lens antenna fabricated on a suspended silicon nitride (SiN) membrane. The radiation is coupled to the leaky wave antenna using a Si lens placed on top of it at a distance of 6 μm. The radiation absorbing section of the KID is fabricated entirely from aluminum, and integrated with the antenna to absorb power from both polarizations directly in the detector. We measured the device sensitivity in a 100 GHz band around 1.55 THz using a black body calibration source. The device shows photon noise limited performance with a noise-equivalent power below 3x10$^{-19}$ W/Hz$^{1/2}$ and good agreement between the measured and expected optical efficiency. The fractional power ratio between the powers received by the dual polarized detector and by the single polarized counterpart is measured to be a factor 2. This shows that the dual polarized device receives all power from an incoherent source. Additionally, we have measured the antenna beam pattern at the same frequency band and find a good agreement between the measured beam and simulations, which are done in reception. Standard transmission simulations, relying on reciprocity, were found to be not fully correct due of the intrinsic multi-moded nature of the antenna. To verify the frequency coverage, we have measured the detector frequency response using a Michelson interferometer and found broad band coupling in agreement with simulations. The presented design can be upgraded to frequencies up to 10 THz using electron beam lithography. These results indicate that broad band, dual polarization radiation coupling above 1 THz is feasible using antenna coupled KIDs.

Microwave Kinetic Inductance Detectors (MKIDs) provide a technological path towards the high-yield, large-format detector arrays needed for the next generation of experiments. The intrinsically integrated readout components of MKIDs generally give rise to high multiplexing factors, simplified assembly, and streamlined experimental integration. We describe the first MKID arrays fabricated and tested on monolithic 150 mm diameter silicon substrates – a crucial scaling in fabrication capacity that is necessary for future large-scale experiments aiming to incorporate hundreds of thousands of detectors in the coming years. The arrays described here are being developed for the TolTEC millimeter-wave imaging polarimeter being constructed for the 50-meter Large Millimeter Telescope (LMT), with observations planned to begin in early 2019. TolTEC uses dichroic filters to define three physically independent focal planes for operation in observational bands centered at 1.1, 1.4, and 2.0 mm. Each focal plane observes in just one wavelength band, allowing the use of simple to produce, direct-absorption pixel designs with each pixel comprising two detectors that are sensitive to orthogonal states of linear polarization. TolTEC comprises approximately 7,000 polarization sensitive MKIDs designed to operate at a base temperature of 100 mK. The primary working material used for these devices are TiN/Ti/TiN multilayer films, which have several advantageous qualities including: low two-level system noise at the TiN-silicon interface; linear responsivity; uniformity in deposition; and tunable transition temperature, sheet resistance and sheet inductance. We describe the detailed pixel and array layout designs, including focal plane integration and optical coupling via spline-profiled, silicon-platelet, feedhorn-coupled waveguide. We present measurements of full arrays and/or prototype small arrays of devices operating in each of the three observation bands and compare the observed noise and optical performance to that predicted from models and simulations. We also describe the fabrication methods used to produce these large-format arrays with high yield and uniformity.

We are developing lumped-element kinetic inductance detectors (LEKIDs) designed to achieve background-limited sensitivity for far-infrared (FIR) spectroscopy on a stratospheric balloon. The Spectroscopic Terahertz Airborne Receiver for Far-InfraRed Exploration (STARFIRE) will study the evolution of dusty galaxies with observations of the [CII] 158 micron and other atomic fine-structure transitions at z = 0.5 - 1.5, both through direct observations of individual luminous infrared galaxies, and in blind surveys using the technique of line intensity mapping. The spectrometer requires large format arrays of dual-polarization-sensitive detectors with NEPs of 1e-17 W/sqrt(Hz). We pattern the LEKIDs in 20-nm aluminum film, and use an array of profiled feedhorns to couple optical radiation onto the meandered inductors. A backshort etched from the backside to a buried oxide layer insures high absorption efficiency without additional matching layers. Initial testing on small sub-arrays has demonstrated a high device yield and median NEP of 4e-18 W/sqrt(Hz). We describe the development and characterization of kilo-pixel arrays using a combination of dark noise measurements and optical response with our cryogenic blackbody.

In the last decades, a very large effort has been made to measure, with high sensitivity, the intensity and spectral contents of millimetric (mm) and submillimetric (submm) light from the Universe. Today this picture is in the way to be routinely completed by polarization measurements that give access to previously hidden processes, for example the traces of primordial gravitational waves in the case of CMB (mainly mm), or the effect of magnetic field for star formation mechanisms (submm and mm optical ranges). The classical way to measure the light polarization is to split the two components by a polarizer grid and record intensities with two conjugated detection setups. This approach implies the deployment of a complex instrument system, very sensitive to external constraints (vibrations, alinement, thermal expansion…), or internal ones: determine low degrees of polarization implies a large increase in sensitivity when compared with intensity measurements. The need of detector arrays, with in pixel polarization measurement capabilities, has been well understood for years: all the complexity being reported at the focal plane level. Subsequently, the instrument integration, verification and tests procedure is considerately alleviated, specially for space applications. All silicon bolometer arrays using the same micromachining techniques than the Herschel PACS modules are well suited for this type of development. New thermometers doped for 50 mK operations permit to achieve, with a new design, sensitivities close to the aW/√Hz. It is based on all-legs bolometers (ALB), where the absorbing, insulating and thermometric functions are made by the same suspended silicon structure. This ALB structure, with in this case a spiral design, permits to separate the absorption of the two electromagnetic components of the light polarization. Each pixel consists of four bolometer divided in two pairs, each sensitive to one direction of polarization. This permits to combine the bolometer bridges in a fully differential global structure with a Wheatstone bridge arrangement. Total intensity and polarization unbalance are available directly at the detector level, thanks to a cold readout circuit integrated in the detector structure. This combination of functions is achieved by above IC manufacture techniques (IC for Integrated Circuit). All these developments take place in the prospect of the joint JAXA-ESA SPICA project, to equip a 1344 pixels polarimetric and imaging camera covering three spectral bands (100, 200 and 350 µm).

Microwave Kinetic Inductance Detectors (MKIDs) have held promise as the focal plane sensing elements in large-format imaging arrays for over a decade and have now found application in several ground-based instruments. In this presentation, we discuss the first implementation of MKIDs for a suborbital instrument in the Balloon-borne Large Aperture Submillimeter Telescope – The Next Generation (BLAST-TNG), a suborbital imaging array designed to study the role magnetic fields play in star formation and bridge the angular scales between Planck’s low resolution all-sky maps and ALMA’s ultra-high resolution narrow fields. BLAST-TNG is scheduled to launch from Antarctica in December 2018. This experiment will utilize 8 times as many polarization sensitive detectors and will have 16 times greater mapping speed compared to its predecessor BLASTpol. This will also be a demonstration for future MKID instruments for ground based telescopes, e.g. TolTEC arrays on the LMT, as well as proposed space based missions. We have built three, large-format MKID arrays for BLAST-TNG. Each monolithic 100mm diameter array is sensitive to a different waveband centered at 250 micron, 350 micron, or 500 micron; together comprising 3318 individual polarization-sensitive detectors. The detector arrays are read out with high levels of multiplexing, with each microwave feedline addressing between 466 and 938 unique resonators depending on the array. Designing for space-like low photon loads, polarization-sensitivity, different frequency bands, and 275 mK operation all pose unique challenges. We address these challenges by employing feedhorn-coupled, dual-polarization sensitive pixels fabricated from TiN/Ti multilayers that combine high responsivity, high uniformity, low loss, and a tunable superconducting Tc. Here, we present the detailed design and fabrication of these arrays, which includes an optimized quarter wavelength silicon backshort for each band realized by micromachining a silicon on insulator (SOI) wafer, aluminum patching of the TiN/Ti absorbing inductor to increase response and tune the effective optical coupling impedance, and a semi-automated layout scheme to make a stepper-compliant lithography process that tiles identical stepper images across the array and then trims them individually to minimize their frequency scatter and crosstalk. This results in high quality, easily reconfigurable, and uniform arrays of MKIDs. We show measurements that demonstrate high pixel yield, > 98% polarization isolation, and a noise equivalent power (NEP) limited by photon noise at the expected in-flight photon load.

In radio astronomy interferometers where the number of stations is large (in the ALMA case 66 antennas, where 8 digitizers are deployed in each antenna) tuning the digitizers parameters: thresholds and bias, is a process which needs to be repeated several times, therefore finding an algorithm that allows to speed up this process is a critical task. It is quite important to keep the digitizers properly adjusted in order to reach the maximal efficiency of the correlator, specially in a regime of coarse quantization (88% for 2 bits, 96% for 3 bits), and also is critical for avoiding signal artifacts which can degrade the collected data (DC bias or harmonics). This work presents a set of different approaches for automatically tuning the digitizers primary selected as: PID by using a proportional/integrative/derivative controller and defining a system to process a coupled MIMO system as an uncoupled SISO; Fuzzy Logic by making extensive advantage of the expert operator knowledge; and finally an hybrid scheme combining PID and Fuzzy Logic for a rapid and accurate tuning process. The aim of the present work is to evaluate the performance of each tuning method based on metrics like: required tuning time, stability and robustness under different extreme boundary conditions. In addition, we suggest the means for collecting the needed information considering an usual interferometer architecture. Furthermore, we provide an automated approach to find the best sampler's clock timing profile. The aim of this work is to provide a guideline for implementing an algorithm which allows to tune a large set of digitizers under different conditions in a fast and precise automated process. The produced report will come in handy for integration into interferometer projects comprising a large number of individual stations (ALMA, SKA, VLA, CHIME, MeerKAT).

GUSTO will be a NASA balloon borne terahertz observatory to be launched from Antarctica in late 2021 for a flight duration of 100-170 days. It aims at reviewing the life cycle of interstellar medium of our galaxy by simultaneously mapping the three brightest interstellar cooling lines: [OI] at 4.7 THz, [CII] at 1.9 THz, and [NII] at 1.4 THz; along the 124 degrees of the galactic plane and through a part of the Large Magellanic Cloud. It will use three arrays of 4x2 mixers based on NbN hot electron bolometers (HEBs), which are currently the most sensitive mixers for high resolution spectroscopic astronomy at these frequencies.

Here we report on the design of a novel 4.7 THz receiver for GUSTO. The receiver consists mainly of two subsystems: a 4×2 HEB quasi-optical mixer array and a 4.7 THz multi-beam LO. We describe the mixer array, which is designed as a compact monolithic unit. We show, for example, 10 potential HEB detectors with the state of the art sensitivity of 720 K measured at 2.5 THz. They have a small variation in sensitivity, being less than 3%, while also meet the LO uniformity requirements. For the multi-beam LO we demonstrate the combination of a phase grating and a single QCL at 4.7 THz, which generates 8 sub-LO beams, where the phase grating shows an efficiency of 75%. A preliminary concept for the integrated LO unit, including QCL, phase grating and beam matching optics is presented.

The ALMA telescope has been producing ground-breaking science since 2011, but it is mostly based on front-end and back-end technology from the 2000s. In order to keep ALMA competitive in the coming decade, timely updates are necessary in order to further improve the science output of the telescope. In NAOJ, we have been doing research leading to technological developments which aim to increase the field-of-view of the telescope, and the RF and instantaneous bandwidth for more efficient and accurate spectral surveys. In this contribution, we will describe the most important technical achievements by our group in recent years.

In ALMA, considerable effort is being made to realize a long-baseline observation and a high-frequency observation. To be implemented these observations, it is required to deliver a high-stable LO signal with frequency switching capability. For high-frequency observations, the frequency switching function is indispensable to compensate atmospheric scintillation. We propose a photonic local oscillator (LO) system capable of satisfying required performances without any modifications on the ALMA antenna side. Furthermore, a direct photonic LO system over a large broadband system has a capable of being applied to the next generation ALMA, and advanced Radio Interferometers. In this paper, the high-frequency LO signal is generated and transmitted as a beat signal of dual-wavelength optical signal. The final purpose of this research is to provide a direct photonic LO system with a cable transmission correction over a large broadband from microwave to terahertz frequencies for advanced Radio Interferometers.

We present a conceptual framework of planar SIS mixer array receivers and the studies on the required techniques. This concept features membrane-based on-chip waveguide probes and a quasi-two-dimensional local-oscillator distribution waveguide network. This concept allows sophisticated functions, such as dual-polarization, balanced mixing and sideband separation, easily implemented with the SIS mixer array in the same planar circuit. We have developed a single-pixel prototype receiver by implementing the concept in the design. Initial measurement results show good evidences that support the feasibility of the concept.

The Greenland Telescope (GLT) project and the East Asian Observatory (EAO) successfully commissioned the first light GLT instrument at the James Clerk Maxwell Telescope (JCMT) in Hawaii, prior to transferring the instrument to Greenland. The GLT instrument which comprises of a cryostat with three cartridge-type receivers (at 86GHz, 230GHz and 345GHz) was installed into the receiver cabin of JCMT and operated in three modes: - (a) Regular JCMT observing with the GLT instrument, using ACSIS, (JCMT’s autocorrelation spectrometer) as the backend and JCMT software for telescope control, data reduction, pointing and antenna focus adjustment. (b) Single dish observations of astronomical spectral line sources, recording data onto mark 6 recorders for offline data reduction. (c) eSMA interferometer array observations at 230GHz in conjunction with the SMA. In this paper, we report on the installation and integration of the GLT instrument at JCMT, present results from commissioning and show how the success of the GLT instrument commissioning fits with our plans for future instrumentation at JCMT.

The Greenland Telescope project has recently participated in an experiment to image the supermassive black hole shadow at the center of M87 using Very Long Baseline Interferometry technique in April of 2018. The antenna consists of the 12-m ALMA North American prototype antenna that was modified to support two auxiliary side containers and to withstand an extremely cold environment. The telescope is currently at Thule Air Base in Greenland with the long-term goal to move the telescope over the Greenland ice sheet to Summit Station. The GLT currently has a single cryostat which houses three dual polarization receivers that cover 84-96 GHz, 213-243 GHz and 271-377 GHz bands. A hydrogen maser frequency source in conjunction with high frequency synthesizers are used to generate the local oscillator references for the receivers. The intermediate frequency outputs of each receiver cover 4-8 GHz and are heterodyned to baseband for digitization within a set of ROACH-2 units then formatted for recording onto Mark-6 data recorders. A separate set of ROACH-2 units operating in parallel provides the function of auto-correlation for real-time spectral analysis. Due to the stringent instrumental stability requirements for interferometry a diagnostic test system was incorporated into the design. Tying all of the above equipment together is the fiber optic system designed to operate in a low temperature environment and scalable to accommodate a larger distance between the control module and telescope for Summit Station. A report on the progress of the above electronics instrumentation system will be provided.

Here we present the preliminary and final designs of a low-mass, low-power, highly integrated Schottky diode based coherent receiver system suitable for deployment on cubesat or other small satellite platforms. Currently, coherent Schottky receivers are far too large and consume too much power to be considered for deployment on any smaller forms of space-based satellites. Using an already existing design for a modular 520-600 GHz receiver designed at JPL, we have used novel packaging methods to condense this receiver into an integrated system. This integrated receiver has shown to have a volume and power consumption significantly smaller than the current state of the art. We will further present the designs of a similar integrated receiver for the first excited state of water vapor operating at the 1040-1200 GHz range. Finally, we discuss future plans for the combined mixer system and its potential for use in cubesat interferometry systems.

To enable the next-generation of bolometric cameras, we are developing the microwave SQUID multiplexer (μMUX). Upcoming receivers such as Simons Observatory, CCAT-prime, BICEP array, Ali-CPT, and CMB-S4 plan to instrument focal planes with 50,000-500,000 sensors. Sensor count is achieved by tiling many 150 mm-diameter densely packed detector arrays into these focal planes. The fabrication and quality of large-format bolometer arrays has been demonstrated and is now mature. In contrast, the readout technology required for next-generation receivers needs development. The sensitivity, low cross-talk, high multiplexing density, and small component size make the μMUX well-suited for this goal. In this approach, the TES signal modulates the inductance of an rf-SQUID that loads a high-Q microwave resonator. The coupled signal therefore modulates the microwave resonance frequency, which may be read out using homodyne techniques. By coupling each resonator to the same microwave feedline, many detectors can be read out on a single coaxial cable pair. The multiplexing density is in practice limited by signal bandwidth, allowable cross-talk, and the digitization bandwidth of room-temperature readout electronics. We present the design and performance of a scalable 64-channel multiplexer chip optimized for bolometric applications. We utilize a new quarter wave resonator design that increases the physical linear density by a factor of two, therefore achieving a smaller footprint for simplified detector packaging. Measurements of this design show 100 kHz resonator bandwidth, uniform 1.8 MHz frequency spacing, and an input referred current noise of 35 pA/√Hz that is well below the level of an optimized, background-limited TES bolometer. Using 8 daisy-chained and frequency scaled chips, we create a 512-channel multiplexer and use it to readout a 512 TES-bolometer array. We present the results of this large-scale μMUX demonstration including system yield, signal cross-talk, and an analysis of noise in various TES bias configurations. The result demonstrates the multiplexing density required to read out 2,000 sensors between 4-8 GHz.

The next generation of cryogenic CMB and submillimeter cameras under development require densely instrumented sensor arrays to meet their science goals. The readout of large numbers (~10,000-100,000 per camera) of sub-Kelvin sensors, for instance as proposed for the CMB-S4 experiment, will require substantial improvements in cold and warm readout techniques. To reduce the readout cost per sensor and integration complexity, efforts are presently focused on achieving higher multiplexing density while maintaining readout noise subdominant to intrinsic detector noise and presenting manageable thermal loads. Highly-multiplexed cold readout technologies in active development include Microwave Kinetic Inductance Sensors (MKIDs) and microwave rf-SQUIDs. Both exploit the high quality factors of superconducting microwave resonators to densely channelize sub-Kelvin sensors into the bandwidth of a microwave transmission line. In the case of microwave SQUID multiplexing, arrays of transition-edge sensors (TES) are multiplexed by coupling each TES to its own superconducting microwave resonator through an rf-SQUID. We present advancements in the development of a new warm readout system for microwave SQUID multiplexing, the SLAC Superconducting Microresonator RF electronics, or SMuRF, by adapting SLAC National Accelerator Laboratory's Advanced Telecommunications Computing Architecture (ATCA) FPGA Common Platform. SMuRF aims to read out 4000 microwave SQUID channels between 4 and 8 GHz per RF line. Each compact SMuRF system is built onto a single ATCA carrier blade. Daughter boards on the blade implement RF frequency-division multiplexing using FPGAs, fast DACs and ADCs, and an analog up- and down-conversion chain. The system reads out changes in flux in each resonator-coupled rf-SQUID by monitoring the change in the transmitted amplitude and frequency of RF tones produced at each resonator's fundamental frequency. The SMuRF system is unique in its ability to track each tone, minimizing the total RF power required to readout each resonator, thereby significantly reducing the linearity requirements on the cold and warm readout. Here, we present measurements of the readout noise and linearity of the first full SMuRF system, including a demonstration of closed-loop tone tracking on a 528 channel cryogenic microwave SQUID multiplexer. SMuRF is being explored as a potential readout solution for a number of future CMB projects including Simons Observatory, BICEP Array, CCAT-prime, Ali-CPT, and CMB-S4. In addition, parallel development of the platform is underway to adapt SMuRF to read out both MKID and fast X-ray TES calorimeter arrays.

SAFARI is one of the focal-plane instruments for the European/ Japanese far-IR SPICA mission proposed for the ESA M5 selection. It is based on three arrays with in total 3550 TES-based bolometers with noise-equivalent powers (NEP) of 2∙10-19 W/Hz. The arrays are operated in three wavelength bands: S-band for 30-60 µm, M-band for 60-110 µm and L-band for 110-210 µm, and have high optical efficiency. SRON is developing Frequency Domain Multiplexing (FDM) for readout of large AC biased TES arrays for both the SAFARI instrument, and the XIFU instrument on the X-ray Athena mission. In FDM for SAFARI, the TES bolometers are AC biased and read out using 24 channels. Each channel contains 160 pixels of which the resonance frequencies are defined by in-house developed cryogenic lithographic LC filters. FDM is based on the amplitude modulation of a carrier signal, which also provides the AC voltage bias, with the signal detected by the TES. To overcome the dynamic range limitations of the SQUID pre-amplifier, baseband feedback (BBFB) is applied. BBFB attempts to cancel the error signal in the sum-point, at the input coil of the SQUID, by feeding back a remodulated signal to the sum-point, and therefore improving the dynamic range of the SQUID pre-amplifier. Previously we have reported on a detailed study of the effects of electrical crosstalk using our first iteration of a prototype of the full 160 pixel FDM experiment and the successful readout of 132 pixels using our 176 pixel FDM system. After the demonstration it is important to perform more detailed measurements to consolidate the system. For instance, one of the important next steps is to expose the FDM system to an optical infrared source. The cold part of the FDM system consists of a detector chip with 176 pixels with a designed NEP of 7∙10-19 W/Hz and two matching LC filter chips, each of which contains 88 carefully placed high-Q resonators, with a total of 176 different resonance frequencies, and a single-stage SQUID. The warm electronics consist of a low-noise amplifier (LNA) and a digital board on which the generation of the bias carriers, the demodulation of the signal and remodulation of the feedback signal are performed. The optical experiment will be conducted in a Leiden Cryogenics dilution refrigerator with a cooling power of about 200µW at 100 mK. This system contains multiple optical sources. These include a conical black body radiator which can be operated in the range of 3-34K and a light pipe through which the experiment can be illuminated from outside the cryostat. Dark measurements are conducted in a Janis ADR system with a base temperature of 50mK. In this paper we describe the experimental tests and results of the more detailed testing of our 176 pixel TES bolometer system.

Traveling-wave parametric amplifiers based on superconducting NbTiN films are being developed that provide gain over nearly an octave of bandwidth at microwave frequencies. The amplifiers are non-linear transmission lines, where the nonlinearity comes from the current dependence of the kinetic inductance. Amplification results from three and four-wave mixing processes, and phase matching over a wide frequency range is achieved by engineering the dispersion characteristics of the transmission line. Recent noise measurements over a wide frequency band demonstrate that the added noise of these amplifiers is close to one half photon, consistent with the quantum limit for a phase preserving amplifier. We will discuss applications of this class of amplifier to astronomical instruments.

The Cosmic Microwave Background (CMB) has provided an invaluable source of information about the universe we live in. However, much information is yet to be gained. For instance, information about the cosmological parameters of dark energy, inflation, and the neutrino sector is nearly guaranteed to provide revolutionary results in upcoming CMB experiments. The current most popular detector technology, TES bolometers, finds a challenge in its low-noise readout, which requires a per-detector strong voltage bias while being able to sense O(10 aW/rtHz) fluctations in incident power. Frequency-multiplexed (fMUX) readout has been demonstrated to great success with an O(10) multiplexing factor, and is currently being implemented with an O(100) multiplexing factor for SPT-3G and POLARBEAR-2. We are developing a series of improvements that will greatly simplify the fMUX readout architecture, improve performance, and increase the multiplexing factor. I will present results on a lossless method of fMUX detector bias that simplifies the readout architecture, as well as an effort to radically change and further simplify the readout architecture by moving the 4K DC SQUID to the sub-Kelvin stage.

Digital frequency multiplexing (dfMux) is a readout architecture for transition edge sensor-based detector arrays and is used on telescopes including SPT-3G, POLARBEAR-2, and LiteBIRD. Here, we present recent progress and plans for development of a sub-Kelvin SQUID architecture for digital frequency multiplexed bolometers. This scheme moves the SQUID from the 4K stage to the 250mK stage, adjacent to the bolometers. Operating the SQUID on the detector stage may offer lower noise and greater scalability. Electrical performance will be improved as a result of decreased wiring length and reduced parasitics, allowing for higher multiplexing factors and lower bolometer R_normal. These performance improvements will enable ultra-large focal planes for future instruments such as CMB-S4.

Advanced ACTPol (AdvACT) is a third generation upgrade to the Atacama Cosmology Telescope (ACT) designed to measure the temperature and polarization anisotropies of the Cosmic Microwave Background (CMB) across five frequency bands. ACT is an off-axis Gregorian telescope with a 6 m primary reflector and 2 m secondary reflector located at a remote site in the Chilean Atacama Desert. AdvACT repurposes the second generation ACTPol receiver, replacing elements where needed while upgrading to a set of kilo-pixel dichroic transition edge sensor bolometer arrays. The AdvACT upgrade has been deployed in stages. The first new array was deployed in 2016, observing at 230 and 150 GHz. The following two arrays were deployed in 2017, observing at 150 and 90 GHz. These upgrades approximately doubled the number of detectors (to ~6,000) when compared to the second generation instrument, ACTPol. The fourth array, designed to observe at 39 and 27 GHz, will be the last to be deployed. The increase in detector count and wide frequency coverage enables a wide range of science goals which include improving constraints on dark energy, the sum of the neutrino masses, and primordial gravitational waves. Command and control of the telescope is performed remotely. A team of collaboration members, referred to as remote observers, has formed to take shifts controlling the telescope throughout the season. Each shift lasts for 24 hours, during which the assigned remote observer is responsible for scheduling the day’s observations, coordinating with the engineering crew at the site, and recovering the telescope should it cease operations. To facilitate these tasks we have designed a set of web tools. The utility of these tools ranges from monitoring telescope systems, data flow, and computer status to scheduling observations and controlling the telescope itself. New tools are simple to integrate and are added as needed. Science and housekeeping data collection, processing, and transfer are largely autonomous. The telescope control tools command the readout electronics which interface with the detectors. Data are collected on one of three computers, one for each detector array, and processed into a standardized, compressed format before being stored in a RAID near the site. A copy is then automatically made on a transport disk, which is used to transfer the data to North America where another copy is then made for data analysis. AdvACT is now in its second season of observations. In this work we describe the status of the AdvACT project and discuss the telescope systems and operations.

Many applications in astronomy from tens of GHz to THz frequencies, on the ground and in space, would benefit from silicon optics because silicon's high refractive index and low loss make it an ideal optical material at these frequencies. Silicon can also be used for ambient temperature vacuum windows, however, it's large refractive index necessitates an antireflection coating. Moreover, multilayer antireflection treatments are necessary for wide spectral bandwidths, with wider bandwidths requiring more layers. To this end, we are developing multilayer coatings for silicon by bonding together wafers individually patterned with deep reactive ion etching (DRIE). While a standard approach to antireflection coating is to deposit or laminate dielectric layers of appropriate refractive index, it is difficult (but not impossible) to find low loss dielectrics with the correct refractive index and other properties to match silicon well, especially if more than one layer is required, operation up to THz frequencies is desired, and/or the optic will be used cryogenically. Textured surfaces are an attractive alternative to dielectric antireflection coatings. For millimeter wavelengths, multi-layer antireflection textures with up to 4:1 bandwidths have been cut successfully into silicon lens surfaces with a dicing saw, but this technique becomes unusable at frequencies of 300 GHz and higher given the saw dimensions. Laser machining is being explored but demonstrations are not yet available. DRIE works well on flat surfaces (and has been demonstrated for narrowband windows to THz frequencies), but there are limits to the depth and aspect ratio of the features it can create. Furthermore, etching has not been adapted to large, curved optics. We are pursuing a hybrid approach to this problem: construct a silicon optic by stacking flat patterned wafers. The starting point is a multilayer optical design incorporating both an axial gradient in the refractive index for antireflection and a radial index gradient for focusing. For each optical layer, a hole or post pattern is used to achieve the required effective index of refraction. Using a novel multilayer etching procedure, several layers of the optical structure are fabricated on a flat wafer. Several individually patterned wafers are stacked and bonded together to produce the completed optic. This approach can thus address the aspect ratio limitations of DRIE, and it obviates etching on curved surfaces. We present our results to date, which include simulations, fabrication and measurements of 2- and 4-layer coatings with wafer-bonding, on high resistivity silicon wafers, at 75-330 GHz. The good agreement between the simulations and the test results validates the fabrication and test setup, and allows us to continue the development of larger bandwidth and more efficient coatings. Our near-term goal is to produce a 10-cm lens with a 7-layer coating providing 5.5:1 bandwidth from 75 to 420 GHz, with less than 1% reflection, eventually scaling up to 15-cm, 30-cm, and larger elements.

In this paper we discuss the latest developments of the STRIP instrument of the “Large Scale Polarization Explorer” (LSPE) experiment. LSPE is a novel project that combines ground-based (STRIP) and balloon-borne (SWIPE) polarization measurements of the microwave sky on large angular scales to attempt a detection of the “B-modes” of the Cosmic Microwave Background polarization. STRIP will observe approximately 25% of the Northern sky from the “Observatorio del Teide” in Tenerife, using an array of forty-nine coherent polarimeters at 43 GHz, coupled to a 1.5 m fully rotating crossed-Dragone telescope. A second frequency channel with six-elements at 95 GHz will be exploited as an atmospheric monitor. At present, most of the hardware of the STRIP instrument has been developed and tested at sub-system level. System-level characterization, starting in July 2018, will lead STRIP to be shipped and installed at the observation site within the end of the year. The on-site verification and calibration of the whole instrument will prepare STRIP for a 2-years campaign for the observation of the CMB polarization.

The SPT-3G receiver was commissioned in early 2017 on the 10-meter South Pole Telescope (SPT) to map anisotropies in the cosmic microwave background (CMB). New optics, detector, and readout technologies have yielded a multichroic, high-resolution, low-noise camera with impressive throughput and sensitivity, offering the potential to improve our understanding of inflationary physics, astroparticle physics, and growth of structure. We highlight several key features and design principles of the new receiver, and summarize its performance to date.

The cosmic microwave background (CMB) radiation is an afterglow of the Big Bang. It contains the crucial keys to understand the beginning of the universe. In particular, the odd-parity patterns of CMB polarization, B-modes, at more than degree-scale, are the best probe to detect primordial gravitational waves at the cosmic inflation. The GroundBIRD experiment aims to detect this large angular scale patterns from the ground. The experiment employs novel techniques; a high-speed rotational scanning system (20 revolution-per-minutes) with cold optics below 4K, and microwave kinetic inductance detectors (MKIDs) as the focal plane detectors. The fast scanning modulation is a crucial characteristic in our observation strategy to mitigate effects of the atmospheric fluctuation. The telescope rotates and scans the sky along the azimuth at the elevation angle of 60 degrees at Teide observatory in the Canary Islands. It allows us to measure CMB polarization patterns at a wide multipole range, 6 < \ell < 300, i.e. aiming to catch the reionization bump. We have developed a telescope mount with 3-axis rotation mechanism (azimuth, elevation, and boresight). We are evaluating the vibration at the focal plane position with rotating the telescope mount. The focal plane consists of seven hexagonal corrugated horn coupled MKIDs array: six hexagon units are for 145 GHz band (55 pixels/unit), and one unit is for 220 GHz band (112 pixels). Each pixel consists of a corrugated horn, a planner OMT, millimeter wave circuits for transmission of dual-polarization signals with the suppression of crosstalk modes, and two MKIDs for each polarization. Magnetic shields are also mounted so as to suppress the external magnetic fields. Trapped magnetic fields inside of the superconducting materials decrease the performance of the MKID. The geomagnetism is the static and large magnetic fields. The telescope motion makes modulation of the geomagnetism as well as the modulation of CMB signals. Therefore, we need careful evaluation associating with the telescope rotation. By using a small evaluation system with modulated magnetic fields, we understand impacts the magnetic shield as well as responses of the MKID for the modulated magnetic field. We design the shield based on them. In this presentation, we will report an evaluation of detector responses on the high-speed rotating system along the azimuth. We will also show demonstrations of our own readout electronics which is well matching with the rapid scan modulation strategy.

The next generation of cosmic microwave background (CMB) experiments, such as CMB-S4, will require large arrays of multi-chroic, polarisation-sensitive pixels. Arrays of lumped-element kinetic inductance detectors (LEKIDs) optically coupled through an antenna and transmission line structure are a promising candidate for such experiments. Through initial investigations of small prototype arrays, we have shown this compact device architecture can produce intrinsic quality factors < 10^5, allowing for MUX ratios to exceed 10^3. Moreover, we have demonstrated that additional noise from two-level systems can be reduced to an acceptable level by removing the dielectric from over the capacitive region of the KID, while retaining the microstrip coupling into the inductor. To maximise the efficiency of future focal planes, it is desirable to observe multiple frequencies simultaneously within each pixel. Therefore, we utilise the proven transmission line coupling scheme to introduce band-defining structures to our pixel architecture. Initially targeting the peak of the CMB at 150-GHz, we present a preliminary study of these narrow-band filters in terms of their spectral bandwidth and out of band rejection. By incorporating simple in-line filters we consider the overall impact of adding such structures to our pixel by investigating detector performance in terms of noise and quality factor. Based on these initial results, we present preliminary designs of an optimised mm-wave diplexer that is used to split-up the 150 GHz atmospheric window into multiple sub-bands, before reaching the absorbing length of the LEKID. We present measurements from a set of prototype filter-coupled detectors as the first demonstration towards construction of large-format, multi-chroic, antenna-coupled LEKIDs with the sensitivity required for future CMB experiments.

We report on the design, fabrication and measured performance of hierarchical sinuous-antenna phased arrays coupled to cryogenic lithographed detectors for millimeter-wave astronomy. This architecture allows for dual-polarization wideband sensitivity with a beam width that is approximately frequency-independent. This solves a common problem with multichroic pixels, which is that the beam width varies with frequency and causes suboptimal sensitivity in most frequency bands. We achieve a variable pixel size, i.e., a multiscale focal plane, by creating phased arrays from neighboring lenslet-coupled sinuous antennas, where the size of each array is chosen independently for each frequency band, so that the effective pixel size scales with wavelength. Our devices consist of arrays of hemispherical lenses coupled to lithographed wafers, which integrate transition-edge-sensor (TES) bolometers with superconducting sinuous antennas and microwave circuitry including band-defining filters. The design can be straightforwardly modified for use with non-TES lithographed cryogenic detectors such as kinetic inductance detectors (KIDs). We have demonstrated frequency-independent beam widths from a three-level hierarchical sinuous-antenna phased array over a 3:1 bandwidth. Additionally, we have demonstrated several other microwave components such as a 4:1 broadband 180-degree hybrid that can simplify the design of future multichroic focal planes including but not limited to hierarchical phased arrays. We discuss the development of a 4-band hierarchical phased array that is scalable in the sense that it can tile a wafer for use in a current or upcoming experiment.

Current and future Cosmic Microwave Background (CMB) polarization anisotropy measurements demand large (10⁴-10⁵) numbers of high-performing detectors in order to unveil minute signals. At the forefront of the detector options available to this field are transition-edge sensor (TES) bolometers, which use superconducting thin films as extremely sensitive thermistors. Understanding the behavior of these TESes is critical to leveraging their full potential and identifying trade-offs between robustness and sensitivity in their design. In this work, we report on measurements of TES bolometers designed for the Advanced ACTPol (AdvACT) upgrade to the Atacama Cosmology Telescope (ACT). Using a three-stage SQUID amplifier chain, time-division multiplexing electronics, and an external signal generator, we characterize the impedance and noise properties of a set of test TES bolometers measured in the laboratory, encompassing various designs, over a wide signal band. Using the impedance data, we are able to explore deviations from the assumed bolometer model in use for TES design and instrument sensitivity forecasts. Modeling these deviations as the result of decoupling of bolometer elements, we extract parameters describing this extended model. We are then able to compare the noise spectra of the devices to forward modeling based on the TES parameters in the extended model. We explore how excess noise varies, and conclude with a discussion of how our results can be useful for designing future TES arrays based on the expected impact of the measured effects on instrumental sensitivities, and the relevance of these results to bolometer designs for upcoming CMB experiments like Simons Observatory and CMB-S4.

Future ground-based cosmic microwave background (CMB) experiments will require more than $10^5$ polarization sensitive pixels covering multiple atmospheric bands. The scientific potential for such an experiment is impressive; however, the technical challenges are daunting: such an instrument will require square meters of focal plane covered in background limited cryogenic detectors and a dramatic increase in readout capability. We are developing novel kinetic inductance detectors (KIDs) optimized for this purpose. These devices use a twin-slot microwave antenna, superconducting Nb transmission line, and a novel coupling scheme that deposits mm-wavelength power onto a high-resistivity meander deposited as the first layer on a bare Si wafer. This architecture allows us to independently adjust the detector and antenna properties and to pursue multi-band designs. We have fabricated superconducting resonators made from atomic layer deposited (ALD) titanium nitride (TiN), with thicknesses ranging from 3 to 40 nm. We find a strong dependence of transition temperature on thickness, from 0.6 to 4.2 K for our thinnest and thickest films, respectively. In dark measurements, we find internal quality factors that range from $10^4$ to $7\times 10^5$ depending on film thickness, and kinetic inductance as high as 8 nH/square. The very small volumes and high kinetic inductance make it possible to engineer extremely sensitive detectors with inductor volumes approaching a few cubic microns that operate at readout frequencies of tens to hundreds of MHz. By taking advantage of the large fractional bandwidth available at low frequencies, we expect to achieve multiplexing densities that exceed that of state of the art TES arrays even without further improvements in film quality factor. We will present the characterization of film properties and dark devices, as well as well as initial optical results for antenna coupled single-band and single-pol devices. We will also discuss designs and sensitivity projections for future dual-pol and multi-band arrays ready for deployment in near-future CMB instruments.

The European/Japanese SPace Infrared telescope for Cosmology and Astrophysics, SPICA, will provide astronomers with a long awaited new window on the universe. Having a large cold telescope cooled to less than 8K above absolute zero, SPICA will provide a unique environment where instruments are limited only by the cosmic background itself. A consortium of European, north American and Asian institutes has been established to design and implement the SpicA FAR infrared Instrument SAFARI, an extremely sensitive spectrometer designed to fully exploit this extremely low far infrared background environment provided by the SPICA observatory. SAFARI’s extremely sensitive Transition Edge Sensing detectors will allow astronomers to very efficiently obtain moderate to high resolution spectra of many thousands of obscured celestial objects in the far infrared, allowing a full spectroscopic characterisation of this objects. Efficiently obtaining such a large number of complete spectra will be essential to address several fundamental questions in current astrophysics: how do galaxies form and evolve over cosmic time?, what is the true nature of our own Milky Way?, and why and where do planets like those in our own solar system come into being? The basic SAFARI instrument is a highly sensitive Grating Spectrometer with a spectral resolution R of about 300 and a line sensitivity of a few x 10^-20 W/√Hz (5σ-1h). By routing the signal through a Martin-Puplett interferometer a high resolution mode is implemented providing R~11000 at 34 μm to R~1500 at 230 μm. The instrument operates in four wavelength bands, simultaneously covering the full 34-230μm range. Each band has three arrays of about 300 TES sensors providing three spatial and 300 spectral outputs. To limit the number of signal wires between the cold focal plan and the warm electronics units a 160 pixel/channel Frequency Domain Multiplexing scheme is employed.

SuperSpec is an integrated, on-chip spectrometer for millimeter and sub-millimeter astronomy. We report the approach, design optimization, and partial characterization of a 300 channel filterbank covering the 185 to 315 GHz frequency band that targets a resolving power R ~ 310, and fits on a 3.5×5.5 cm chip. SuperSpec uses a lens and broadband antenna to couple radiation into a niobium microstrip that feeds a bank of niobium microstrip half-wave resonators for frequency selectivity. Each half-wave resonator is coupled to the inductor of a titanium nitride lumped-element kinetic inductance detector (LEKID) that detects the incident radiation. The device was designed for use in a demonstration instrument at the Large Millimeter Telescope (LMT).

HIRMES is a far-infrared spectrometer that was chosen as the third generation instrument for NASA's SOFIA airborne observatory. HIRMES promises background limited performance in four modes that cover the wavelength range between 25 and 122 μm. The high-spectral resolution (R ≈10⁵) mode is matched to achieve maximum sensitivity on velocity-resolved lines to study the evolution of protoplanetary disks. The mid-resolution (R≈12,000) mode is suitable for high sensitivity imaging of galactic star formation regions in, for example, the several far-infrared fine structure lines. The low-resolution (R≈2000) imaging mode is optimized for spectroscopic mapping of far-infrared fine structure lines from nearby galaxies, while the low resolution (R≈600) grating spectrometer mode is optimized for detecting dust and ice features in protostellar and protoplanetary disks. Several Transition Edge Sensed (TES) bolometer arrays will provide background limited sensitivity in each of these modes. To optimize performance in the various instrument modes, HIRMES employs eight unique fully-tunable cryogenic Fabry-Perot Interferometers (FPIs) and a grating spectrometer. Here we present the design requirements and the mechanical and optical characteristics and performance of these tunable FPI as well as the control electronics that sets the mirror separation and allows scanning of the FPIs.

Since the development of the instrument PACS on the HERSCHEL space observatory, the silicon bolometers technology is well understood and handled at CEA. Our pixels are based on a well-known concept of electromagnetism: the absorber closes a quarter-wave cavity which allows to get maximal absorption at the corresponding wavelength. In the frame of the SPICA mission and more precisely for the SAFARI-pol instrument, we have designed and manufactured new absorbers with a different pattern that enables detectors to be sensitive to the polarization. In this way, the measurement of the polarized (sub)millimeter radiation is directly performed within the pixel. Similarly, we want to introduce a spectroscopic capacity inside the chip. In this talk, we will present the interferometric system that has been designed to fulfill the spectroscopic requirements of a space mission. The physics on which rely the interferences of multiple waves inside the detector will be largely developed. In the last part, we will describe the inverse process that follows the data acquisition, and will be carried out from the spectrometer chip characterization. The final aim of this research is to pave the way to bolometer focal planes with polarimetry and spectroscopy capabilities inside the detectors.  

SuperSpec is an on-chip filter-bank spectrometer designed for wideband moderate-resolution spectroscopy at millimeter and submillimeter wavelengths. Employing TiN kinetic inductance detectors, the device has demonstrated noise performance suitable for photon noise limited ground-based observations at excellent millimeter-wave observing sites. In these proceedings we present a demonstration instrument featuring six independent single-polarization SuperSpec chips, covering 190-310 GHz with 300 channels. We summarize spectrometer performance, describe the cryostat and optical coupling, and present the readout and telescope control system. In an initial deployment to the Large Millimeter Telescope, we plan to observe submillimeter galaxies in [CII] emission at redshifts 5 < z < 9 and CO emission from lower-redshift galaxies. Real on-sky performance will inform the design of the next generation of instruments using large numbers of SuperSpec devices, which could include multi-object spectrometers or line intensity mapping experiments that target [CII] during the Epoch of Reionization.

The next generation inflationary satellite probe, LiteBIRD, aims to detect B-mode polarization at degree scales and larger. With 2,622 detectors, LiteBIRD will observe the sky using a reflector Low-Frequency Telescope (LFT) ranging from 40 – 235 GHz, and a refractor High-Frequency Telescope (HFT) ranging from 280 – 402 GHz. This allows for the characterization and subtraction of synchrotron foregrounds at low frequencies and thermal dust foregrounds at high frequencies. The U.S. LiteBIRD team proposes to deliver detector arrays, along with readout electronics, using lenslet-coupled sinuous antenna arrays in the LFT, and orthomode-transducer-coupled corrugated horn arrays in the HFT, both utilizing TES bolometer detectors cooled to 100 mK base temperatures. With insight from the Planck space mission, we know that an important consideration to make for the LiteBIRD experiment is the effect of cosmic ray impacts on low-ell systematics and data selection efficiency. The two primary mechanisms for these effects are events in on the 100 mK stage causing low-frequency variation in focal-plane temperature, and the propagation of ballistic phonons into nearby detectors causing “glitches”, or pulses in bolometer timestreams. LiteBIRD estimates a 5% data loss due to cosmic ray, utilizing straightforward mitigation techniques to increase thermal sinking and heat capacity of the detector wafers. We report on initial characterization and mitigation of ballistic phonon propagation in prototype detector wafers using 5.49 MeV alpha particles from an Americium-241 source. We look to present test results from mitigation techniques including removal of bulk silicon around the bolometer island, adding palladium and other conductors around the bolometer island, removal of the niobium ground plane around the bolometer island, and variations of the preceding methods.

CCAT-prime will be a 6-meter aperture telescope operating from sub-mm to mm wavelengths, located at 5600 meters elevation on Cerro Chajnantor in the Atacama Desert in Chile. Its novel crossed-Dragone optical design will deliver a high throughput, wide field of view capable of illuminating much larger arrays of sub-mm and mm detectors than can existing telescopes. We present an overview of the motivation and design of Prime-Cam, a first-light instrument for CCAT-prime. Prime-Cam will house seven instrument modules in a 1.8 meter diameter cryostat, cooled by a dilution refrigerator. The optical elements will consist of silicon lenses, and the instrument modules can be individually optimized for particular science goals. The current design enables both broad- band, dual-polarization measurements and narrow-band, Fabry-Perot spectroscopic imaging using multichroic transition-edge sensor (TES) bolometers operating between 190 and 450 GHz. It also includes broadband kinetic induction detectors (KIDs) operating at 860 GHz. This wide range of frequencies will allow excellent characterization and removal of galactic foregrounds, which will enable precision measurements of the sub-mm and mm sky. Prime-Cam will be used to constrain cosmology via the Sunyaev-Zeldovich effects, map the intensity of [CII] 158 μm emission from the Epoch of Reionization, measure Cosmic Microwave Background polarization and foregrounds, and characterize the star formation history over a wide range of redshifts. More information about CCAT-prime can be found at www.ccatobservatory.org.

The far-IR band is uniquely suited to study the physical conditions in the interstellar medium from nearby sources out to the highest redshifts. FIR imaging and spectroscopy instrumentation using incoherent superconducting bolometers represents a high sensitivity technology for many future suborbital and space missions, including the Origins Space Telescope. Robust, high sensitivity detector arrays with several 104 pixels, large focal plane filling factors, and low cosmic ray cross sections that operate over the entire far-IR regime are required for such missions. These arrays could consist of smaller sub-arrays, in case they are tileable. The TES based Backshort Under Grid array architecture which our group has fielded in a number of FIR cameras, is a good candidate to meet these requirements: BUGs are tileable, and with the integration of the SQUID multiplexer scaleable beyond wafer sizes; they provide high filling factors, low cosmic cross section and have been demonstrated successfully in far-infrared astronomical instrumentation. However, the production of BUGs with integrated readout multiplexers has many time and resource consuming process steps. In order to meet the requirement of robustness and efficiency on the production of future arrays, we have developed a new method to provide the superconducting connection of BUG detectors to the readout multiplexers or general readout boards behind the detectors. This approach should allow us to reach the goal to produce reliable, very large detector arrays for future FIR missions.

Ultra-low-noise Transition Edge Sensors (TESs) have been selected for the far-infrared Fourier transform spectrometer SAFARI on the space telescope SPICA, now under study as an M5 mission, operating in three wavelength bands: S-band from 34-60 μm, M-band from 60-110 μm and L-band from 110-210 μm. We report the fabrication and optical characterisation of a linear TES array for the SAFARI M-band, integrated with micromachined reflective backshorts and profiled pyramidal optical feedhorns. The design and construction of the cryogenic optical test facility used to illuminate the devices under test are described, featuring a variable temperature blackbody load, band-defining filters and an optical aperture. We observe effective numbers of optical modes, Nef f = 0.41 ± 0.03, and near-unity optical efficiencies in TES-backshort assemblies, with some loss of efficiency in the presence of horns. Stray light control measures are discussed in the context of a significant reduction achieved in long wavelength stray light detected by these devices.

With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves. We demonstrate this effect with focal plane arrays of absorber coupled Lumped Element microwave Kinetic Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the response from a point source at the pixel position is at a similar level to the stray response integrated over the entire chip area. For the antenna coupled arrays, we show that this effect can be suppressed by incorporating an on-chip stray light absorber. A similar method should be possible with the LEKID array, especially when they are lens coupled.

The Cosmology Large Angular Scale Surveyor (CLASS) aims to detect and characterize the primordial Bmode signal and make a sample-variance-limited measurement of the optical depth to reionization. CLASS is a ground-based, multi-frequency microwave polarimeter that surveys 70% of the microwave sky every day from the Atacama Desert. The focal plane detector arrays of all CLASS telescopes contain smooth-walled feedhorns that couple to transition-edge sensor (TES) bolometers through symmetric planar orthomode transducer (OMT) antennas. These low noise polarization-sensitive detector arrays are fabricated on mono-crystalline silicon wafers to maintain TES uniformity and optimize optical efficiency throughout the wafer. In this paper, we discuss the design and characterization of the first CLASS 93 GHz detector array. We measure the dark parameters, bandpass, and noise spectra of the detectors and report that the detectors are photon-noise limited. With current array yield of 82%, we estimate the total array noise-equivalent power (NEP) to be 2.1 aW√s.

The third-generation instrument for the 10-meter South Pole Telescope, SPT-3G, was first installed in January 2017. In addition to completely new cryostats, secondary telescope optics, and readout electronics, the number of detectors in the focal plane has increased by an order of magnitude from previous instruments to ~16,000. The SPT-3G focal plane consists of ten detector modules, each with an array of 269 trichroic, polarization-sensitive pixels on a six-inch silicon wafer. Within each pixel is a broadband, dual-polarization sinuous antenna; the signal from each orthogonal linear polarization is divided into three frequency bands centered at 95, 150, and 220 GHz by in-line lumped element filters and transmitted via superconducting microstrip to Ti/Au transition-edge sensor (TES) bolometers. Properties of the TES film, microstrip filters, and bolometer island must be tightly controlled to achieve optimal performance. For the second year of SPT-3G operation, we have replaced all ten wafers in the focal plane with new detector arrays tuned to increase mapping speed and improve overall performance. Here we discuss the TES superconducting transition temperature and normal resistance, detector saturation power, bandpasses, optical efficiency, and full array yield for the 2018 focal plane.

The Simons Observatory (SO) will provide precision polarimetry of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales from arc-minutes to tens of degrees, contain over 60,000 detectors, and observe in frequency bands between 27 GHz and 270 GHz. SO will consist of a six-meter-aperture telescope initially coupled to roughly 35,000 detectors along with an array of half-meter aperture refractive cameras, coupled to an additional 30,000+ detectors.

The large aperture telescope receiver (LATR) is coupled to the SO six-meter crossed Dragone telescope and will be 2.4 m in diameter, weigh over 3 metric tons, and have five cryogenic stages (80 K, 40 K, 4 K, 1 K and 100 mK). The LATR is coupled to the telescope via 13 independent optics tubes containing cryogenic optical elements and detectors. The cryostat will be cooled by two Cryomech PT90 (80 K) and three Cryomech PT420 (40 K and 4 K) pulse tube cryocoolers, with cooling of the 1 K and 100 mK stages by a commercial dilution refrigerator system. The secondo component, the small aperture telescope (SAT), is a single optics tube refractive cameras of 42 cm diameter. Cooling of the SAT stages will be provided by two Cryomech PT420, one of which is dedicated to the dilution refrigeration system which will cool the focal plane to 100 mK. SO will deploy a total of three SATs.

In order to estimate the cool down time of the camera systems given their size and complexity, a finite difference code based on an implicit solver has been written to simulate the transient thermal behavior of both cryostats. The result from the simulations presented here predict a 35 day cool down for the LATR. The simulations suggest additional heat switches between stages would be effective in distribution cool down power and reducing the time it takes for the LATR to reach its base temperatures. The SAT is predicted to cool down in one week, which meets the SO design goals.

The Cosmology Large Angular Scale Surveyor consists of four instruments performing a CMB polarization survey. Currently, the 40 GHz and first 90 GHz instruments are deployed and observing, with the second 90 GHz and a multichroic 150/220 GHz instrument to follow. The receiver is a central component of each instrument's design and functionality. This paper describes the CLASS receiver design, using the first 90 GHz receiver as a primary reference. Cryogenic cooling and filters maintain a cold, low-noise environment for the detectors. We have achieved receiver detector temperatures below 50mK in the 40 GHz instrument for 85% of the initial 1.5 years of operation, and observed in-band efficiency that is consistent with pre-deployment estimates. At 90 GHz, less than 26% of in-band power is lost to the filters and lenses in the receiver, allowing for high optical efficiency. We discuss the mounting scheme for the filters and lenses, the alignment of the cold optics and detectors, stray light control, and magnetic shielding.

The Simons Observatory (SO) will make precision temperature and polarization measurements of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales between one arcminute and tens of degrees and sample frequencies between 27 and 270 GHz. Here we present the current design of the large aperture telescope receiver (LATR), a 2.4m diameter cryostat that will be mounted on the SO 6m telescope and will be the largest CMB receiver to date. The cryostat size was chosen to take advantage of the large focal plane area having high Strehl ratios, which is inherent to the Cross-Dragone telescope design. The LATR will be able to accommodate thirteen optics tubes, each having a 36 cm diameter aperture and illuminating several thousand transition-edge sensor (TES) bolometers. This set of equipment will provide an opportunity to make measurements with unparalleled sensitivity. However, the size and complexity of the LATR also pose numerous technical challenges. In the following paper, we present the design of the LATR and include how we address these challenges. The solutions we develop in the process of designing the LATR will be informative for the general CMB community, and for future CMB experiments like CMB-S4.

We present the design and characterization of a ground-based absolute polarization angle calibrator accurate to better than 0.1° for use with polarization sensitive cosmic microwave background (CMB) experiments. The calibrator's accuracy requirement is driven by the need to reduce upper limits on cosmic polarization rotation, which is expected to be zero in a large class of cosmological models. Cosmic polarization effects such as cosmic birefringence and primordial magnetic fields can generate spurious B-modes that result in non-zero CMB TB and EB correlations that are degenerate with a misalignment of detector orientation. Common polarized astrophysical sources used for absolute polarization angle calibration have not been characterized to better than 0.5°. Higher accuracy can be achieved through self-calibration methods, however these are subject to astrophysical foreground contamination and inherently assume the absence of effects like cosmic polarization rotation. The deficiencies in these two calibration methods highlight the need for a well characterized polarized source. The calibrator we present utilizes a 76 GHz Gunn oscillator coupled to a frequency doubler, pyramidal horn antenna, and co-rotating wire-grid polarizer. A blackened optics tube was built around the source in order to mitigate stray reflections, attached to a motor-driven rotation stage, then mounted in a blackened aluminum enclosure for further reflection mitigation and robust weatherproofing. We use an accurate bubble level in combination with four precision-grade aluminum planes located within the enclosure to calibrate the source's linear polarization plane with respect to the local gravity vector to better than the 0.1° goal. In 2017 the calibrator was deployed for an engineering test run on the POLARBEAR CMB experiment located in Chile's Atacama Desert and is being upgraded for calibration of the POLARBEAR-2b receiver in 2018. In the following work we present a detailed overview of the calibrator design, systematic control, characterization, deployment, and plans for future CMB experiment absolute polarization calibration.

QUBIC, the Q & U Bolometric Interferometer for Cosmology, is a novel ground-based instrument that has been designed to measure the extremely faint B-mode polarisation anisotropy of the cosmic microwave background at intermediate angular scales (multipoles of 𝑙 = 30 − 200). Primordial B-modes are a key prediction of Inflation as they can only be produced by gravitational waves in the very early universe. To achieve this goal, QUBIC will use bolometric interferometry, a technique that combines the sensitivity of an imager with the systematic error control of an interferometer. It will directly observe the sky through an array of 400 back-to-back entry horns whose signals will be superimposed using a quasi-optical beam combiner. The resulting interference fringes will be imaged at 150 and 220 GHz on two focal planes, each tiled with NbSi Transition Edge Sensors, cooled to 320 mK and read out with time-domain multiplexing. A dichroic filter placed between the optical combiner and the focal planes will select the two frequency bands. A very large receiver cryostat will cool the optical and detector stages to 40 K, 4 K, 1 K and 320 mK using two pulse tube coolers, a novel 4He sorption cooler and a double-stage 3He/4He sorption cooler. Polarisation modulation and selection will be achieved using a cold stepped half-wave plate (HWP) and polariser, respectively, in front of the sky-facing horns. A key feature of QUBIC’s ability to control systematic effects is its ‘self-calibration’ mode where fringe patterns from individual equivalent baselines can be compared. When observing, however, all the horns will be open simultaneously and we will recover a synthetic image of the sky in the I, Q and U Stokes’ parameters. The synthesised beam pattern has a central peak of approximately 0.5 degrees in width, with secondary peaks further out that are damped by the 13-degree primary beam of the horns. This is Module 1 of QUBIC which will be installed in Argentina, near the city of San Antonio de los Cobres, at the Alto Chorrillos site (4869 m a.s.l.), Salta Province. Simulations have shown that this first module could constrain the tensor-to-scalar ratio down to σ(r) = 0.01 after a two-year survey. We aim to add further modules in the future to increase the angular sensitivity and resolution of the instrument. The QUBIC project is proceeding through a sequence of steps. After an initial successful characterisation of the detection chain, a technological demonstrator is being assembled to validate the full instrument design and to test it electrically, thermally and optically.

The technical demonstrator is a scaled-down version of Module 1 in terms of the number of detectors, input horns and pulse tubes and a reduction in the diameter of the combiner mirrors and filters, but is otherwise similar. The demonstrator will be upgraded to the full module in 2019. In this paper we give an overview of the QUBIC project and instrument.

Bicep Array is a cosmic microwave background (CMB) polarization experiment that will begin observing at the South Pole in early 2019. This experiment replaces the five Bicep2 style receivers that compose the Keck Array with four larger Bicep3 style receivers observing at six frequencies from 30 to 270GHz. The 95GHz and 150GHz receivers will continue to push the already deep Bicep/Keck CMB maps while the 30/40GHz and 220/270GHz receivers will constrain the synchrotron and galactic dust foregrounds respectively. Here we report on the design and performance of the Bicep Array instruments focusing on the mount and cryostat systems.

The compelling science case for the observation of B-mode polarization in the cosmic microwave background (CMB) is driving the CMB community to expand the observed sky fraction, either by extending survey sizes or by deploying receivers to potential new northern sites. For ground-based CMB instruments, poorly-mixed atmospheric water vapor constitutes the primary source of short-term sky noise. This results in short-timescale brightness fluctuations, which must be rejected by some form of modulation. To maximize the sensitivity of ground-based CMB observations, it is useful to understand the effects of atmospheric water vapor over timescales and angular scales relevant for CMB polarization measurements. To this end, we have undertaken a campaign to perform a coordinated characterization of current and potential future observing sites using scanning 183 GHz water vapor radiometers (WVRs). So far, we have deployed two identical WVR units; one at South Pole, Antarctica, and the other at Summit Station, Greenland. The former site has a long heritage of ground based CMB observations and is the current location of the Bicep/Keck Array telescopes and the South Pole Telescope. The latter site, though less well characterized, is under consideration as a northern-hemisphere location for future CMB receivers. Data collection from this campaign began in January 2016 at South Pole and July 2016 at Summit Station. Data analysis is ongoing to reduce the data to a single spatial and temporal statistic that can be used for one-to-one site comparison.

We present a preliminary study of the sky scanning strategy for the LSPE-STRIP instrument, a ground-based telescope that will be installed at the Teide Observatory (Tenerife, Canary Islands) in early 2019 and will observe the polarized emission of about 25% of the sky in the Northern Hemisphere at 43 and 95 GHz. The same sky portion will be observed at 140, 220 and 240 GHz by LSPE-SWIPE, a stratospheric balloon scheduled for a long-duration flight around the North Pole during the Arctic winter of 2019/2020. The combination of data from the two instruments aims at constraining the tensor-to-scalar ratio down to r ~ 0.03. In our paper we discuss the main scanning strategy requirements (overlap with SWIPE coverage, sensitivity distribution, observation of calibration sources) and show how we obtain a trade-off by spinning the telescope around the azimuth axis with constant elevation and angular velocity. The combination of the telescope motion with the Earth rotation will guarantee the access to the large angular scales. We will observe periodically the Crab Nebula as well as the Perseus molecular cloud. The Crab is one of the best known polarized sources in the sky and it will be observed for calibration purposes. The second one is a source of Anomalous Microwave Emission that could be characterized both in intensity and polarization.

BICEP Array is a degree-scale Cosmic Microwave Background (CMB) experiment that will search for primordial B-mode polarization while constraining Galactic foregrounds. BICEP Array will be comprised of four receivers to cover a broad frequency range with channels at 30/40, 95, 150 and 220/270 GHz. The first low-frequency receiver will map synchrotron emission at 30 and 40 GHz and will deploy to the South Pole at the end of 2019. In this paper, we give an overview of the BICEP Array science and instrument, with a focus on the detector module. We designed corrugations in the metal frame of the module to suppress unwanted interactions with the antenna-coupled detectors that would otherwise deform the beams of edge pixels. This design reduces the residual beam systematics and temperature-to-polarization leakage due to beam steering and shape mismatch between polarized beam pairs. We report on the simulated performance of single- and wide-band corrugations designed to minimize these effects. Our optimized design alleviates beam differential ellipticity caused by the metal frame to about 7% over 57% bandwidth (25 to 45 GHz), which is close to the level due the bare antenna itself without a metal frame. Initial laboratory measurements are also presented.

In this activity, we develop novel focal plane detector pixels for the next generation CMB B mode detection missions. Such future mission designs will require focal plane pixel technologies that optimizes the coupling from telescope optics to the large number of detectors required to reach the sensitivities required to measure the faint CMB polarization traces. As part of an ESA Technical Research Programme (TRP) programme we are tasked with developing, manufacturing and experimentally verifying a prototype multichroic pixel which would be suitable for the large focal plane arrays to reduce the focal plane size requirement. The concept of replacing traditional single channel pixels with multi frequency pixels will be a key driver in future mission design and the ability to couple radiation effectively over larger bandwidths (30 - 100%) is a real technical challenge. In the initial part of the programme we reviewed the science drivers and this determined the technical specifications of the mission. Various options for focal plane architectures were considered and then after a tradeoff study and review of resources available, a pixel demonstrator was selected for design manufacture and test. The chosen design consists of a novel planar mesh lens coupling to various planar antenna configurations with Resonant Cold Electron Bolometer (RCEB) for filtering and detection of the dual frequency signal. The final cryogenic tests are currently underway and a final performance will be verified for this pixel geometry.

QUBIC, the Q & U Bolometric Interferometer for Cosmology, is a novel ground-based instrument that aims to measure the extremely faint B-mode polarisation anisotropy of the cosmic microwave background at intermediate angular scales (multipoles of 𝑙 = 30 − 200). Primordial B-modes are a key prediction of Inflation as they can only be produced by gravitational waves in the very early universe. To achieve this goal, QUBIC will use bolometric interferometry, a technique that combines the sensitivity of an imager with the immunity to systematic effects of an interferometer. It will directly observe the sky through an array of back-to-back entry horns whose beams will be superimposed using a cooled quasioptical beam combiner. Images of the resulting interference fringes will be formed on two focal planes, each tiled with transition-edge sensors, cooled down to 320 mK. A dichroic filter placed between the optical combiner and the focal planes will select two frequency bands (centred at 150 GHz and 220 GHz), one frequency per focal plane. Polarization modulation will be achieved using a cold stepped half-wave plate (HWP) and polariser in front of the sky-facing horns.

The full QUBIC instrument is described elsewhere^1,2,3,4; in this paper we will concentrate in particular on simulations of the optical combiner (an off-axis Gregorian imager) and the feedhorn array. We model the optical performance of both the QUBIC full module and a scaled-down technological demonstrator which will be used to validate the full instrument design. Optical modelling is carried out using full vector physical optics with a combination of commercial and in-house software. In the high-frequency channel we must be careful to consider the higher-order modes that can be transmitted by the horn array. The instrument window function is used as a measure of performance and we investigate the effect of, for example, alignment and manufacturing tolerances, truncation by optical components and off-axis aberrations. We also report on laboratory tests carried on the QUBIC technological demonstrator in advance of deployment to the observing site in Argentina.

Targeting faint polarization patterns arising from Primordial Gravitational Waves in the Cosmic Microwave Background requires excellent observational sensitivity. Optical elements in small aperture experiments such as Bicep3 and Keck Array are designed to optimize throughput and minimize losses from transmission, reflection and scattering at millimeter wavelengths. As aperture size increases, cryostat vacuum windows must withstand larger forces from atmospheric pressure and the solution has often led to a thicker window at the expense of larger transmission loss. We have identified a new candidate material for the fabrication of vacuum windows: with a tensile strength two orders of magnitude larger than previously used materials, woven high-modulus polyethylene could allow for dramatically thinner windows, and therefore significantly reduced losses and higher sensitivity. In these proceedings we investigate the suitability of high-modulus polyethylene windows for ground-based CMB experiments, such as current and future receivers in the Bicep/Keck Array program. This includes characterizing their optical transmission as well as their mechanical behavior under atmospheric pressure. We find that such ultra-thin materials are promising candidates to improve the performance of large-aperture instruments at millimeter wavelengths, and outline a plan for further tests ahead of a possible upcoming field deployment of such a science-grade window.

The Atacama Cosmology Telescope (ACT) is a 6 m telescope located in the Atacama Desert, designed to measure the cosmic microwave background (CMB) with arcminute resolution. ACT, with its third generation polarization sensitive array, Advanced ACTPol, is being used to measure the anisotropies of the CMB in five frequency bands in large areas of the sky (~ 15,000 deg²). These measurements are designed to characterize the large scale structure of the universe, test cosmological models and constrain the sum of the neutrino masses. As the sensitivity of these wide surveys increases, the control and validation of the far sidelobe response becomes increasingly important and is particularly challenging as multiple reflections, spillover, diffraction and scattering become difficult to model and characterize at the required levels. In this work, we present a ray trace model of the ACT upper structure which is used to describe much of the observed far sidelobe pattern. This model combines secondary mirror spillover measurements with a 3D CAD model based on photogrammetry measurements to simulate the beam of the camera and the comoving ground shield. This simulation shows qualitative agreement with physical optics tools and features observed in far sidelobe measurements. We present this method as an efficient first-order calculation that, although it does not capture all diffraction effects, informs interactions between the structural components of the telescope and the optical path, which can then be combined with more computationally intensive physical optics calculations. This method can be used to predict sidelobe patterns in the design stage of future optical systems such as the Simons Observatory, CCAT-prime, and CMB Stage IV.

The search for inflationary primordial gravitational waves and the measurement of the optical depth to reionization, both through their imprint on the large angular scale correlations in the polarization of the cosmic microwave background (CMB), has created the need for high sensitivity measurements of polarization across large fractions of the sky at millimeter wavelengths. These measurements are subject to instrumental and atmospheric 1=f noise, which has motivated the development of polarization modulators to facilitate the rejection of these large systematic effects.

Variable-delay polarization modulators (VPMs) are used in the Cosmology Large Angular Scale Surveyor (CLASS) telescopes as the first element in the optical chain to rapidly modulate the incoming polarization. VPMs consist of a linearly polarizing wire grid in front of a movable flat mirror. Varying the distance between the grid and the mirror produces a changing phase shift between polarization states parallel and perpendicular to the grid which modulates Stokes U (linear polarization at 45°) and Stokes V (circular polarization). The CLASS telescopes have VPMs as the first optical element from the sky; this simultaneously allows a lock-in style polarization measurement and the separation of sky polarization from any instrumental polarization further along in the optical path.

The CLASS VPM wire grids use 50 μm copper-plated tungsten wire with a 160μm spacing across a 60 cm clear aperture. The mirror is mounted on a flexure system with one degree of translational freedom, enabling the required mirror motion while maintaining excellent parallelism with respect to the wire grid. The wire grids and mirrors are held parallel to each other to better than 80 μm, and the wire grids have RMS flatness errors below 50 μm across the 60 cm aperture. The Q-band CLASS VPM was the first VPM to begin observing the CMB full time, starting in the Spring of 2016. The first W-band CLASS VPM was installed in the Spring of 2018.

BICEP3 is a 520mm aperture on-axis refracting telescope observing the polarization of the cosmic microwave background (CMB) at 95GHz in search of the B-mode signal originating from in ationary gravitational waves. BICEP3's focal plane is populated with modularized tiles of antenna-coupled transition edge sensor (TES) bolometers. BICEP3 was deployed to the South Pole during 2014-15 austral summer and has been operational since. During the 2016-17 austral summer, we implemented changes to optical elements that lead to better noise performance. We discuss this upgrade and show the performance of BICEP3 at its full mapping speed from the 2017 and 2018 observing seasons. BICEP3 achieves an order-of-magnitude improvement in mapping speed compared to a Keck 95GHz receiver. We demonstrate 6.6μK√s noise performance of the BICEP3 receiver.

We present here a study of the use of the SiAl alloy CE7 for the packaging of silicon devices at cryogenic temperatures. We report on the development of baseplates and feedhorn arrays for millimeter wave bolometric detectors for astrophysics. Existing interfaces to such detectors are typically made either of metals, which are easy to machine but mismatched to the thermal contraction profile of Si devices, or of silicon, which avoids the mismatch but is difficult to directly machine. CE7 exhibits properties of both Si and Al, which makes it uniquely well suited for this application.

We measure CE7 to a) superconduct below a critical transition temperature, T_c, ~1.2 K, b) have a thermal contraction profile much closer to Si than metals, which enables simple mating, and c) have a low thermal conductivity which can be improved by Au-plating. Our investigations also demonstrate that CE7 can be machined well enough to fabricate small structures, such as #0-80 threaded holes, to tight tolerances (~25 μm) in contrast with pure silicon and similar substrates. We have fabricated CE7 baseplates being deployed in the 93 GHz polarimetric focal planes used in the Cosmology Large Angular Scale Surveyor (CLASS).¹ We also report on the development of smooth-walled feedhorn arrays made of CE7 that will be used in a focal plane of dichroic 150/220 GHz detectors for the CLASS High-Frequency camera.

Complex field measurements are increasingly becoming the standard for state-of-the-art astronomical instrumentation. Complex field measurements have been used to characterize a suite of ground, airborne, and space-based heterodyne receiver missions,^1-6 and a description of how to acquire coherent field maps for direct detector arrays was demonstrated in Davis et. al. 2017⁷. This technique has the ability to determine both amplitude and phase radiation patterns from individual pixels on an array for direct comparison to optical simulations. Phase information helps to better characterize the optical performance of the array (as compared to total power radiation patterns) by constraining the fit in an additional plane.⁴ This is a powerful technique to diagnose optical alignment errors through the optical system, as a complex field scan in an arbitrary plane can be propagated either forwards or backwards through optical elements to arbitrary planes along the principal axis. Complex radiation patterns have the advantage that the effects of optical standing waves and alignment errors between the scan system and the instrument can be corrected and removed during post processing.

Here we discuss the mathematical framework used in an analysis pipeline developed to process complex field radiation pattern measurements. This routine determines and compensates misalignments of the instrument and scanning system. We begin with an overview of Gaussian beam formalism and how it relates to complex field pattern measurements. Next we discuss a scan strategy using an offset in z along the optical axis that allows first-order optical standing waves between the scanned source and optical system to be removed in post-processing. Also discussed is a method by which the co- and cross-polarization fields can be extracted individually for each pixel by rotating the two orthogonal measurement planes until the signal is the co-polarization map is maximized (and the signal in the cross-polarization field is minimized). We detail a minimization function that can fit measurement data to an arbitrary beam shape model. We conclude by discussing the angular plane wave spectral (APWS) method for beam propagation, including the near-field to far-field transformation.

The Event Horizon Telescope (EHT) is a very-long-baseline interferometry (VLBI) experiment that aims to observe supermassive black holes with an angular resolution that is comparable to the event horizon scale. The South Pole occupies an important position in the array, greatly increasing its north-south extent and therefore its resolution.

The South Pole Telescope (SPT) is a 10-meter diameter, millimeter-wavelength telescope equipped for bolometric observations of the cosmic microwave background. To enable VLBI observations with the SPT we have constructed a coherent signal chain suitable for the South Pole environment. The dual-frequency receiver incorporates state-of-the-art SIS mixers and is installed in the SPT receiver cabin. The VLBI signal chain also includes a recording system and reference frequency generator tied to a hydrogen maser. Here we describe the SPT VLBI system design in detail and present both the lab measurements and on-sky results.

Here we present the characterization of the performance of a novel design for a digital spectrometer that could be used for high resolution cm/mm/submm spectroscopy. The CMOS ASIC spectrometer design, developed at JPL and UCLA, has dramatically lower power consumption than current approaches that generally employ Field Programmable Gate Arrays (FPGAs). Particularly for space missions and for small satellites, power consumption is a major issue. The order of magnitude lower power consumption of the ASIC approach is thus critical for future missions employing large-format focal plane arrays. Our task was to evaluate this 1024 channel, 1.3-GHz bandwidth CMOS spectrometer in terms of stability and filter shape. The chip was to be tested largely at half-maximum speed to allow for use of the polyphase filter bank. The results of this testing show that the ASIC spectrometer can be made to perform largely as expected based on its design parameters, however, they suggest that more testing of the spectrometer chip could be beneficial. Follow-up tests and newer versions of the chip are discussed at the end of the proceeding.

The ASTE (Atacama Submillimeter Telescope Experiment) is a 10-m submillimeter telescope located near the ALMA (Atacama Large Millimeter/submillimeter Array) site in Chile. Recently, the ASTE heterodyne receiver system has been upgraded with a new cryostat and two sub-mm-wave heterodyne receivers. The cryostat has three receiver ports. Its cooling capacity is improved with new design compared to a previous three-cartridge cryostat. The two new receivers are dual polarization Superconductor-Insulator-Superconductor (SIS) sideband-separating receivers in 345 GHz and 460 GHz bands. The 345 GHz band receiver has 55 GHz bandwidth. The single-sideband noise temperature T_SSB measured in the laboratory is between 62 K and 440 K. The 460 GHz band receiver was originally an engineering qualification model of the ALMA Band 8 cartridge. The design of SIS mixer devices has been optimized for full coverage of ALMA Band 8 frequency (385-500 GHz). T_SSB of the receiver is between 98 K and 257 K. The receiver system was installed on ASTE in March 2017. We have started to provide it for open-use observations after our CSV (Commissioning and Science Verification) activities.

We present the design, and prototype phases of the intermediate frequency (IF) system for the upcoming balloon borne observatory, Galactic/Extragalactic Ultra-Long Duration Balloon (ULDB) Spectroscopic Terahertz Ob- servatory (GUSTO). GUSTO is a multi-organizational project whose goal is to address several key unanswered questions concerning all of the phases of the stellar life cycle within the Interstellar Medium (ISM). Using the NASA ULDB system for its platform, GUSTO will employ on-the-fly mapping techniques to scan a total of 124 square degrees of the Milky Way and Large Magellanic Cloud (LMC). GUSTO will survey the three brightest cooling lines in the Milky Way and the LMC. These lines are [CII], [OI], and [NII] corresponding to the three wavelengths of 158, 63, and 205 micron respectively. The completed survey will provide higher angular, and velocity resolution than that of previous surveys of [CII], [OI], and [NII]. These lines will be measured using three 8-pixel heterodyne arrays, each one dedicated to an individual cooling line, and all working together to make a 24-pixel focal plane. The GUSTO IF system is being designed to operate at low power consumption and high sensitivity all in a compact and lightweight package. The IF system will include a wideband 0.3 - 5 GHz, cryogenic, low noise amplifier (LNA), which will boost the IF output of a superconducting hot electron bolometer (HEB) mixer. The LNA was designed with commercial, off the shelf SiGe heterojunction bipolar transistors, and surface mount passive components. The LNA design has been optimized for low power consumption, and for sensitivity. The input impedance of the LNA is matched to the output impedance of the mixer over a wide range of frequencies to reduce reflections, and standing waves. Warm IF electronics have also been designed using commercial, off the shelf, surface mount SiGe transistors in order to achieve a high, and at gain (>50dB) over the entire bandwidth. These components provide variable gain and deliver an optimum signal level to the analog to digital converter of the backend spectrometer. The warm IF components were optimized for wide bandwidth, low power consumption, as well as reliability, and fit in a compact package. Commercially fabricated custom flexible printed circuit boards are being used for multi-channel stripline-based transmission lines, instead of the traditional stainless steel cryogenic semi-rigid coaxial cables. Replacing coaxial cables with the flexible printed circuit boards allows us to transmit through up to 16 lines on a single flex circuit, without losing performance, and furthering the design goal of providing a compact/lightweight solution. Each of the components used in this IF system will undergo rigorous qualification testing, and documentation in accordance with a NASA Class-D balloon mission. We discuss the design challenges in adapting cryogenic, and warm IF electronics to operate for an ultra long duration balloon mission.

We present in this paper a study of a low-power consumption cryogenic amplifier with GaAs-based HEMT. A two-stage MMIC low noise amplifier for 2.5-4.5 GHz frequency range has been designed, fabricated and measured at a low-power condition with the temperature range from 300 K to 4 K. To design such a cryogenic MMIC amplifier, firstly we extracted the model of the bare-die transistor at cryogenic temperatures fabricated together with the MMIC. The temperature-dependent DC and RF characteristics of the HEMT have been measured. From the approximate noise model based on the DC characteristics, we verified that the HEMTs offer sufficient gain and reasonably noise at a relative lowpower operation condition. Subsequently, we designed a low-power dissipation cryogenic MMIC amplifier utilizing the cryogenic s2p model of the HEMTs biased at the optimal low-power condition. At cryogenic temperature, the GaAsbased amplifier achieves a gain larger than 20dB and a noise temperature as low as 10 K with a total power consumption of 1.2 mW. The low-power amplifiers can be used as first-stage IF amplifiers in a superconductor-insulatorsuperconductor (SIS) receiver, and are especially useful in focal plane arrays with large pixel count because of the merit of the total power consumption.

A single feed cryogenic Q-band (35 – 50 GHz) dual-linear polarization receiver is under development at the NRC, primarily to establish the antenna performance parameters of the Dish Verification Antenna 2 at its high-frequency limit and as a possible receiver system for the National Radio Astronomy Observatory’s Next Generation Very Large Array (ngVLA). The cryostat houses a corrugated feed horn cooled to 16 K with a wide opening half-angle of 55°. The linear orthomode transducer (OMT) was redesigned to incorporate noise injection couplers and the power dividing function thus reducing the amount of components, connections, and thermal mass. The low noise (T_LNA = 12 K) amplifier (LNA) was also redesigned to replace coaxial ports with WR-22 waveguide ports. The specifications, receiver design, measured farfield feed horn beam patterns from a near-field planar scanner, simulated OMT results, and sub-20 K receiver noise analysis is presented, along with future plans for production and installation.

The Atacama Large Millimeter/submillimeter Array (ALMA) Band 1 receiver covers the frequency range of 35-50 GHz. An extension of up to 52 GHz is on a best-effort basis. A total of 73 units have to be built in two phases: 8 preproduction and then 65 production units. This paper reports on the assembly, testing, and performance of the preproduction Band 1 receiver. The infrastructure, integration, and evaluation of the fully-assembled Band 1 receiver system will be covered. Finally, a discussion of the technical and managerial challenges encountered for this large number of receivers will be presented.

Phased array feeds (PAFs) are an active research area in radio astronomy, as they offer potential advantages over traditional single-pixel feeds. Their key advantage is increased field of view and survey speed, however they also permit tailoring the antenna beam for A_e=T_sys, or other objectives such as attenuating strong radio frequency interference (RFI). A primary research goal is to improve the noise temperature performance of a PAF over comparable single-pixel feeds.

In this work we have constructed a small 16-element digital beamformer with 384 MHz of bandwidth to evaluate the performance of NRCs Advanced Focal Array Demonstrator (AFAD) operating from 750 to 1500 MHz. We compare measured sensitivity results to previous measurements made with an analog beamformer. The digital beamformer is implemented using NRCs Kermode platform, a Virtex6-based compute blade. We take a standards-based approach, using the AdvancedTCA (ATCA) form factor for the Kermode board, ANSI/VITA-49.0 framing for all chip-to-chip and chip-to-host communications, and AXI4-Stream format for all internal datapaths. The Kermode system can be expanded with a standard ATCA full-mesh backplane to support up to 128 inputs with over 1 GHz of bandwidth.

This expanded capability will ultimately be used to evaluate the performance of the full 96-element AFAD PAF mounted on a re ector antenna. To achieve this goal, we are well into developing a digitizer system that will handle at least 96 elements with up to 1.5 GHz of bandwidth per element. We present an overview of the digitizer system in the context of the PAF beamformer system, and provide an update on the progress to date.

A three-cartridge cryogenic receiver system is constructed for the Greenland Telescope Project. The system is equipped with a set of sub-millimeter receivers operating at 86, 230, and 345 GHz, as well as a complete set of instruments for calibration, control and monitoring. It is single pixel instrument built for VLBI observations. With the receiver system, the GLT has completed commissioning of its 12-m sub-millimeter antenna and participated in global very-long-baseline interferometry (VLBI) observations at Thule Air Base (TAB). This paper describes the receiver specification, construction, and verification.

The Tianlai Pathfinder is designed to demonstrate the feasibility of using wide field of view radio interferometers to map the density of neutral hydrogen in the Universe after the Epoch of Reionizaton. This approach, called 21 cm intensity-mapping, promises an inexpensive means for surveying the large-scale structure of the cosmos. The Tianlai Pathfinnder presently consists of an array of three, 15 m × 40 m cylinder telescopes and an array of sixteen, 6 m diameter dish antennas located in a radio-quiet part of western China. The two types of arrays were chosen to determine the advantages and disadvantages of each approach. The primary goal of the Pathfinder is to make 3D maps by surveying neutral hydrogen over large areas of the sky in two different redshift ranges: first at 1.03 > z > 0.78 (700 - 800 MHz) and later at 0.21 > z > 0.12 (1170-1270 MHz). The most significant challenge to 21 cm intensity-mapping is the removal of strong foreground radiation that dwarfs the cosmological signal. It requires exquisite knowledge of the instrumental response, i.e. calibration. In this paper we provide an overview of the status of the Pathfinder and discuss the details of some of the analysis that we have carried out to measure the beam function of both arrays. We compare electromagnetic simulations of the arrays to measurements, discuss measurements of the gain and phase stability of the instrument, and provide a brief overview of the data processing pipeline.

ALMA has already produced many impressive and scientifically compelling results. However, continuous technical upgrades and development are key for ALMA to continue to lead astronomical research through the 2020-2030 decade and beyond. The East Asia ALMA development program consists of the execution of short term projects, and the planning and initial studies for longer term developments that are essential for future upgrades. We present an overview of all these ongoing East Asia ALMA development projects and upgrade studies, which aim to maintain and even increase the outstanding scientific impact of ALMA in the near future and over the coming decades.

We present the latest results obtained with the wide-field submillimeter camera ArTeMiS that is operating on APEX since July 2013. This camera is presently equipped with 1870 pixels at 350 μm and 800 pixels at 450 μm simultaneously. ArTéMiS is a PI-camera open to the ESO and Swedish community. It has already taken a part in the 2016-2017 scientific results of APEX. So far, it offers the best performance in terms of mapping speed at 350 and 450 μm in the southern hemisphere.

Major improvements of the APEX telescope have been achieved at the end of 2017, requiring a complete removal of the instruments in the C-Cabin. In the meantime, the ArTeMiS camera has been kept safe at the ALMA Operations Support Facility (OSF) building. We took advantage of this re-installation to improve a bit more the optical coupling of detectors. We present here the present status of the camera.

Since APEX operation is now guaranteed until the end of 2022, our prospects are to install in time new detectors presently developed at CEA/Léti in the frame of R&D developments made for the future SPICA space mission. Those detectors, which have new polarization capabilities, are also presented.

SCUBA-2 is a world leading wide field submillimeter camera on the JCMT with two, large format background limited TES arrays, which are used to image simultaneously in the 450μm and 850um atmospheric windows. SCUBA-2 has been producing excellent science for over 6 years however, as we reported previously, excess in-band power loading of the arrays is a concern. One possibility that we considered was that the currently installed hot-pressed filters at the 4K stage were being warmed significantly above 4K by incoming infrared radiation. In an attempt to reduce the power loading we cryogenically tested a new 60K filter stack that incorporated a redesigned thermal blocking filter. A direct comparison was then made to the performance of the existing 60K filter stack installed in SCUBA-2. We saw a tremendous improvement in the infrared rejection with the new design and proceeded to install the new filter stack into SCUBA-2.

In this paper, we describe the testing and installation of the new and improved design of thermal blocking filter into the instrument and report the resulting performance change based on data from the first 12 months of science operation with the new filters. We also present the combined filter bandpass profiles as measured in-situ with FTS-2.

Future generations of far-infrared (FIR) telescopes will need detectors with noise-equivalent powers on the order of 5x10^-20 W/Hz^1/2 in order to be photon background limited by astrophysical sources. One such mission concept in development is the Galaxy Evolution Probe (GEP), which will characterize galaxy formation and evolution from z=0 to beyond z=4. Kinetic inductance detectors (KIDs) have been baselined for the GEP for spectroscopy and imaging science between 10 μm and 400 μm due to their intrinsic frequency multiplexability and simple readout schemes. We focus on quasiparticle recombination times as a strategy for increasing detector responsivities to move towards the NEP requirements of the GEP. We present a new model for quantifying time constants from the responses of detectors to pulses of light, and test this model on a 40 nm thick ¼ λ Al coplanar waveguide KID. We intend to use this measurement scheme to quantify the dependence of the quasiparticle recombination time on Al thickness.

The Sub-millimeter Common-User Bolometer Array 2 (SCUBA-2) large format Transition Edge Sensor (TES) arrays are optimized to maximize mapping speed with two commissioned regular observing scan patterns. The ancillary instruments POLarimeter 2 (POL-2) and Fourier Transform Spectrometer 2 (FTS-2) impose different demands on the arrays compared to regular stand-alone SCUBA-2 observing. This includes a change in the background optical power loading on the arrays and a requirement for a larger dynamic range from the individual TES bolometers. In this paper, we discuss the process for optimizing the TES arrays specifically for POL-2 and FTS-2 operations and report the improvements that we have obtained.

The Tomographic Ionized-carbon Mapping Experiment (TIME) utilizes grating spectrometers to achieve instantaneous wideband coverage with background-limited sensitivity. A unique approach is employed in which curved gratings are used in parallel plate waveguides to focus and diffract broadband light from feed horns toward detector arrays. TIME will measure singly ionized carbon fluctuations from 5 < z < 9 with an imaging spectrometer. 32 independent spectrometers are assembled into two stacks of 16, one per polarization. Each grating has 210 facets and provides a resolving power R of ~ 200 over the 186–324 GHz frequency range. The dispersed light is detected using 2-D arrays of transition edge sensor bolometers. The instrument is housed in a closed-cycle 4K–1K–300mK cryostat. The spectrometers and detectors are cooled using a dual-stage 250/300 mK refrigerator.

SAFARI is a point source spectrometer for the SPICA mission, which provides far-infrared spectroscopy and high sensitivity. SPICA mission, having a large cold telescope cooled to 6K above absolute zero, will provide an optimum environment where instruments are limited only by the cosmic background. SAFARI is a grating-based spectrometer with two modes of operation, Low Resolution (LR), or nominal mode (R~300) and High Resolution, (HR) (R~2000-11000). The SAFARI shall provide point source spectroscopy with diffraction-limited capability in four spectral bands over 34-230μm and a field of view (FoV) on sky over 2’×2’. Due to the complexity of the optical design of the SAFARI instrument a modular design was selected. Four principal modules are defined: Calibration Module (CS), Input Optics Module (IOM), Beam and Mode Distribution (BMDO) and Grating Modules (GMs). The present work is focused in the last module. Dispersive optical systems inherently demand the need of volume allocation for the optical system, being this fact somehow proportional to the wavelength and the required resolving power. The image sampling and the size of the detector elements are key drivers in this optical modular design. The optimization process has been performed taking into account the conceptual design parameters obtained during this phase such as collimator and camera optics focal lengths, subsystem diameters and periods and AOIs of the diffraction gratings.

The design of a mesh filter involves the selection of various grid patterns and their assembly into a multiple layer structure to meet the desired transfer characteristics. This can be a laborious process involving modelling tools and multiple iterations before a satisfactory solution is achieved. Here we report on-going investigations into the use of evolutionary computing (specifically the Micro-Genetic Algorithm) in association with electrodynamic modelling algorithms (the Finite Difference, Time Domain method or a propagation matrix method or both) to automatically arrive at a solution given only the target admittance function. Results are reported for designs utilizing both conventional capacitive and inductive grids (for comparison purposes) as well as for grids containing unconventional pixelated shapes. Drawbacks of the approach are also discussed.

BETTII is a balloon-borne far infrared (FIR: 30-100 μm) interferometer that also uses a near-infrared (NIR: 1-2.5 μm) channel for fine pointing sensing using stars. We have developed an inductive grid dichroic to divide the incoming beam into two components, by reflecting FIR light and transmitting NIR light. The dichroic is fabricated using focused electron beam technology to produce a 1 μm period, 100 nm width metal grid on a sapphire substrate in order to have high reflectance for FIR wavelengths. Here we discuss the design and the detailed manufacturing process for such a dichroic. The transmission and reflectance characteristics are also presented. We discuss them in context of the BETTII requirements.

Here we present a preliminary design for a dielectrically embedded mesh lens, with the intended purpose of being deployed on a 6-unit CubeSat to observe the 556GHz water emission line. A CubeSat offers a cost-effective potential solution for observing these emissions, which cannot be observed from the ground, given it has a lens which can offer a significant effective collecting area at that frequency. To this end, we investigate designs for a lens by using transmission line theory to model a flat, lightweight, dielectrically embedded mesh lens which can be fabricated using layers of photolithographically etched material. We demonstrate that, using commercially available material, transmittances of over 95% may be achieved.

Sub-millimeter polarization observations using the POL-2 instrument mounted on the dual wavelength (850/450 μm) 10 k pixel sub-millimeter camera SCUBA-2 is in high demand on the James Clerk Maxwell Telescope (JCMT). The high level of Instrumental Polarization (IP) generated by the Gore-Tex^TM wind blind protecting the telescope is a hampering factor for these observations. The wind blind both introduces an overall linear polarization and a four lobed polarization footprint seen on strong point sources after removal of a beam averaged IP. During commissioning an IP model was developed for the 850 μm band but a good 450 μm model was lacking. This paper describes the effort to improve the 850 μm IP model, establish a 450 μm model and the work to understand and model the IP. During the work the wind blind was removed for a month to isolate the contribution of the wind blind from other sources of the IP. A theoretical model for the non wind blind generated IP has been developed. However, a theoretical model for the wind blind IP is still being worked on.

CEA has a long history of customizing optoelectronic components for space and astronomy applications. Based on this expertise, we are undertaking the development of cooled silicon bolometers for millimetre-wave (mm-wave) polarization detection in the next generation of space astronomy missions such as SPICA. Silicon bolometer technology has been demonstrated successfully in space conditions through the Herschel mission. There are many benefits of this technology such as the use of a simple and low-power read-out circuit that can be integrated below the detector array in an above-IC (Integrated Circuit) integration scheme. The advanced integration in a large array and the fabrication process based on microelectronics techniques are key challenges for these developments. This work presents the early results on the design, the fabrication and the first characterization of an innovative pixel for mm-wave polarization detection. The aim is to have an adapted absorption around λ=1.5 mm. These bolometers are composed of an absorbing layer and a thermometer, which are thermally insulated from the substrate. To increase the sensitivity, these detectors are working at very low temperature typically between 50 and 100 mK. The suspended thermometer is made of silicon implanted with Phosphorus and Boron species, and we optimized the design to have a high sensitivity with a 3D Variable Range Hopping conduction (Efros law) and a low 1/f noise at low temperature. The heat capacity of the bolometer is optimized by using a meander shape of the thermometer together with superconducting Ti/TiN thin films for the electromagnetic wave absorption. This sensor is implemented on a standard SOI substrate. Measurements of test structures at room temperature, and first results at very low temperature have been performed to evaluate the electrical performances of the fabricated detectors. The mechanical behaviour of released structures, including pixels with a pitch of 1200μm and 600μm, is presented and discussed.

The Primordial In ation Explorer (PIXIE) is an Explorer-class mission concept to measure the gravitational-wave signature of primordial in ation through its distinctive imprint on the linear polarization of the cosmic microwave background. Its optical system couples a polarizing Fourier transform spectrometer to the sky to measure the differential signal between orthogonal linear polarization states from two co-pointed beams on the sky. The double differential nature of the four-port measurement mitigates beam-related systematic errors common to the two-port systems used in most CMB measurements. We describe the polarized beam patterns for PIXIE and assess the systematic error for measurements of CMB polarization.

QUBIC, the QU Bolometric Interferometer for Cosmology, is a novel forthcoming instrument to measure the B-mode polarization anisotropy of the Cosmic Microwave Background. The detection of the B-mode signal will be extremely challenging; QUBIC has been designed to address this with a novel approach, namely bolometric interferometry. The receiver cryostat is exceptionally large and cools complex optical and detector stages to 40 K, 4 K, 1 K and 350 mK using two pulse tube coolers, a novel ⁴He sorption cooler and a double-stage ³He/⁴He sorption cooler. We discuss the thermal and mechanical design of the cryostat, modelling and thermal analysis, and laboratory cryogenic testing.

The POLARBEAR-2/Simons Array Cosmic Microwave Background (CMB) polarization experiment is an upgrade and expansion of the existing POLARBEAR-1 (PB-1) experiment, located in the Atacama desert in Chile. Along with the CMB temperature and E-mode polarization anisotropies, PB-1 and the Simons Array study the CMB B-mode polarization anisotropies produced at large angular scales by inflationary gravitational waves, and at small angular scales by gravitational lensing. These measurements provide constraints on various cosmological and particle physics parameters, such as the tensor-to-scalar ratio r, and the sum of the neutrino masses. The Simons Array consists of three 3.5 m diameter telescopes with upgraded POLARBEAR-2 (PB-2) cryogenic receivers, named PB-2a, -2b, and -2c. PB-2a and -2b will observe the CMB over multiple bands centered at 95 GHz and 150 GHz, while PB-2c will observe at 220 GHz and 270 GHz, which will enable enhanced foreground separation and de-lensing. Each Simons Array receiver consists of two cryostats which share the same vacuum space: an optics tube containing the cold reimaging lenses and Lyot stop, infrared-blocking filters, and cryogenic half-wave plate; and a backend which contains the focal plane detector array, cold readout components, and millikelvin refrigerator. Each PB-2 focal plane array is comprised of 7,588 dual-polarization, multi-chroic, lenslet- and antenna-coupled, Transition Edge Sensor (TES) bolometers which are cooled to 250 mK and read out using Superconducting Quantum Interference Devices (SQUIDs) through a digital frequency division multiplexing scheme with a multiplexing factor of 40. In this work we describe progress towards commissioning the PB-2b and -2c receivers including cryogenic design, characterization, and performance of both the PB-2b and -2c backend cryostats.

The Simons Observatory (SO) will make precision temperature and polarization measurements of the cosmic microwave background (CMB) using a series of telescopes which will cover angular scales between one arcminute and tens of degrees, contain over 60,000 detectors, and sample frequencies between 27 and 270 GHz. SO will consist of a six-meter-aperture telescope coupled to over 30,000 detectors along with an array of half-meter aperture refractive cameras, which together couple to an additional 30,000+ detectors. SO will measure fundamental cosmological parameters of our universe, find high redshift clusters via the Sunyaev-Zeldovich effect, constrain properties of neutrinos, and seek signatures of dark matter through gravitational lensing. In this paper we will present results of the simulations of the SO large aperture telescope receiver (LATR). We will show details of simulations performed to ensure the structural integrity and thermal performance of our receiver, as well as will present the results of finite element analyses (FEA) of designs for the structural support system. Additionally, a full thermal model for the LATR will be described. The model will be used to ensure we meet our design requirements. Finally, we will present the results of FEA used to identify the primary vibrational modes, and planned methods for suppressing these modes. Design solutions to each of these problems that have been informed by simulation will be presented.

The Simons Observatory (SO) is a new experiment that aims to measure the cosmic microwave background (CMB) in temperature and polarization. SO will measure the polarized sky over a large range of microwave frequencies and angular scales using a combination of small (~0.5 m) and large (~6 m) aperture telescopes and will be located in the Atacama Desert in Chile. This work is part of a series of papers studying calibration, sensitivity, and systematic errors for SO. In this paper, we discuss current efforts to model optical systematic effects, how these have been used to guide the design of the SO instrument, and how these studies can be used to inform instrument design of future experiments like CMB-S4. While optical systematics studies are underway for both the small aperture and large aperture telescopes, we limit the focus of this paper to the more mature large aperture telescope design for which our studies include: pointing errors, optical distortions, beam ellipticity, cross-polar response, instrumental polarization rotation and various forms of sidelobe pickup.

In this proceeding, we present studies of instrumental systematic effects for the Simons Obsevatory (SO) that are associated with the detector system and its interaction with the full SO experimental systems. SO will measure the Cosmic Microwave Background (CMB) temperature and polarization anisotropies over a wide range of angular scales in six bands with bandcenters spanning from 27 GHz to 270 GHz. We explore effects including intensity-to-polarization leakage due to coupling optics, bolometer nonlinearity, uncalibrated gain variations of bolometers, and readout crosstalk. We model the level of signal contamination, discuss proposed mitigation schemes, and present instrument requirements to inform the design of SO and future CMB projects.

The Simons Observatory (SO) is a set of cosmic microwave background instruments that will be deployed in the Atacama Desert in Chile. The key science goals include setting new constraints on cosmic inflation, measuring large scale structure with gravitational lensing, and constraining neutrino masses. Meeting these science goals with SO requires high sensitivity and improved calibration techniques. In this paper, we highlight a few of the most important instrument calibrations, including spectral response, gain stability, and polarization angle calibrations. We present their requirements for SO and experimental techniques that can be employed to reach those requirements.

New telescopes are being built to measure the Cosmic Microwave Background (CMB) with unprecedented sensitivity, including Simons Observatory (SO), CCAT-prime, the BICEP Array, SPT-3G, and CMB Stage-4. We present observing strategies for telescopes located in Chile that are informed by the tools used to develop recent Atacama Cosmology Telescope (ACT) and Polarbear surveys. As with ACT and Polarbear, these strategies are composed of scans that sweep in azimuth at constant elevation.

We explore observing strategies for both small (0.42 m) aperture telescopes (SAT) and a large (6 m) aperture telescope (LAT). We study strategies focused on small sky areas to search for inflationary gravitational waves as well as strategies spanning roughly half the low-foreground sky to constrain the effective number of relativistic species and measure the sum of neutrino masses via the gravitational lensing signal due to large scale structure. We present these strategies specifically considering the telescope hardware and science goals of the SO, located at 23° South latitude, 67.8° West longitude.

Observations close to the Sun and the Moon can introduce additional systematics by applying additional power to the instrument through telescope sidelobes. Significant side lobe contamination in the data can occur even at tens of degrees or more from bright sources. Therefore, we present several strategies that implement Sun and Moon avoidance constraints into the telescope scheduling.

Scan strategies can also be a powerful tool to diagnose and mitigate instrumental systematics either by using multiple scans to average down systematics or by providing null tests to diagnose problems. We discuss methods for quantifying the ability of an observation strategy to achieve this.

Strategies for resolving conflicts between simultaneously visible fields are discussed. We focus on maximizing telescope time spent on science observations. It will also be necessary to schedule calibration measurements, however that is beyond the scope of this work. The outputs of this study are algorithms that can generate specific schedule commands for the Simons Observatory instruments.

The Simons Observatory (SO) is an upcoming experiment that will study temperature and polarization fluctuations in the cosmic microwave background (CMB) from the Atacama Desert in Chile. SO will field both a large aperture telescope (LAT) and an array of small aperture telescopes (SATs) that will observe in six bands with center frequencies spanning from 27 to 270 GHz. Key considerations during the SO design phase are vast, including the number of cameras per telescope, focal plane magnification and pixel density, in-band optical power and camera throughput, detector parameter tolerances, and scan strategy optimization. To inform the SO design in a rapid, organized, and traceable manner, we have created a Python-based sensitivity calculator with several state-of-the-art features, including detector-to-detector optical white-noise correlations, a handling of simulated and measured bandpasses, and propagation of low-level parameter uncertainties to uncertainty in on-sky noise performance. We discuss the mathematics of the sensitivity calculation, the calculator's object-oriented structure and key features, how it has informed the design of SO, and how it can enhance instrument design in the broader CMB community, particularly for CMB-S4.

The desire for higher sensitivity has driven ground-based cosmic microwave background (CMB) experiments to employ ever larger focal planes, which in turn require larger reimaging optics. Practical limits to the maximum size of these optics motivates the development of quasi-optically-coupled (lenslet-coupled), multi-chroic detectors. These detectors can be sensitive across a broader bandwidth compared to waveguide-coupled detectors. However, the increase in bandwidth comes at a cost: the lenses (up to ~700 mm diameter) and lenslets (~5 mm diameter, hemispherical lenses on the focal plane) used in these systems are made from high-refractive-index materials (such as silicon or amorphous aluminum oxide) that reflect nearly a third of the incident radiation. In order to maximize the faint CMB signal that reaches the detectors, the lenses and lenslets must be coated with an anti-reflective (AR) material. The AR coating must maximize radiation transmission in scientifically interesting bands and be cryogenically stable. Such a coating was developed for the third generation camera, SPT-3G, of the South Pole Telescope (SPT) experiment, but the materials and techniques used in the development are general to AR coatings for mm-wave optics. The three-layer polytetra uoroethylene-based AR coating is broadband, inexpensive, and can be manufactured with simple tools. The coating is field tested; AR coated focal plane elements were deployed in the 2016-2017 austral summer and AR coated reimaging optics were deployed in 2017-2018.

We present the design and experimental demonstration of a 16-channel frequency domain multiplexing (FDM) readout for transition-edge sensor (TES) bolometers. This readout system is going to be implemented on the LSPE/SWIPE balloon-borne experiment, whose goal is to detect the polarization of cosmic microwave background (CMB) at large angular scales and whose launch is scheduled for December 2019.

We describe the fabrication process of the Niobium superconducting inductors and the qualification tests performed in our 300 mK cryogenic facility in INFN Pisa of the boomerang shaped PCBs hosting the LC chains and the gradiometric SQUIDs, which are going to be mounted on the back of the SWIPE focal planes. The development of the warm readout electronics is presented, together with the firmware for the generation and readout of the biasing frequency comb.

QUBIC (the Q and U Bolometric Interferometer for Cosmology) is a ground-based experiment which seeks to improve the current constraints on the amplitude of primordial gravitational waves. It exploits the unique technique, among Cosmic Microwave Background experiments, of bolometric interferometry, combining together the sensitivity of bolometric detectors with the control of systematic effects typical of interferometers. QUBIC will perform sky observations in polarization, in two frequency bands centered at 150 and 220 GHz, with two kilo-pixel focal plane arrays of NbSi Transition-Edge Sensors (TES) cooled down to 350 mK. A subset of the QUBIC instrument, the so called QUBIC Technological Demonstrator (TD), with a reduced number of detectors with respect to the full instrument, will be deployed and commissioned before the end of 2018.

The voltage-biased TES are read out with Time Domain Multiplexing and an unprecedented multiplexing (MUX) factor equal to 128. This MUX factor is reached with two-stage multiplexing: a traditional one exploiting Superconducting QUantum Interference Devices (SQUIDs) at 1K and a novel SiGe Application-Specific Integrated Circuit (ASIC) at 60 K. The former provides a MUX factor of 32, while the latter provides a further 4. Each TES array is composed of 256 detectors and read out with four modules of 32 SQUIDs and two ASICs. A custom software synchronizes and manages the readout and detector operation, while the TES are sampled at 780 Hz (100kHz/128 MUX rate).

In this work we present the experimental characterization of the QUBIC TES arrays and their multiplexing readout chain, including time constant, critical temperature, and noise properties.

With photon-noise dominated detectors, CMB experiments become more sensitive only by increasing detector count. Current experiments have on the order of 10,000 detectors, and future experiments propose 5-50x that figure. Reading out these large focal planes requires superconducting multiplexing technology. One concern with this technology is its potential to inject false signal into data via magnetic fields. We investigate magnetic field effects and potential shielding solutions within the context of readout electronics made for the South Pole Telescope's SPT-3G camera.

We explore two magnetic shielding technologies: high-μ metals and superconducting shielding. The high-μ shield is a box made of Amuneal A4K, an alloy designed for high permeability at cryogenic temperatures. The box geometry is a half cylinder to allow for simultaneous testing of shielded and unshielded readout electronics. The superconducting shielding is a NbN-coated cover installed around a superconducting filter network. We saw no attenuation of coupling to the applied external field with the A4K box, and the NbN shield amplifies this coupling in its current implementation. We found the A4K box is effective at isolating some coupling to magnetic fields inherent to the readout electronics. Further testing is needed to differentiate neighboring-SQUID effects from other intermodule coupling before evaluating the NbN shield's crosstalk isolation capability.

LiteBIRD is a satellite project to measure the polarization of the CMB with an unprecedented accuracy. LiteBIRD observes all sky for three years at the sun-earth second Lagrange point. The goal of LiteBIRD is to observe the B-mode polarization at large angular scales and to measure the tensor-to-scaler ratio r with an accuracy less than 0.001, exploring the energy scale of the inflation. In order to mitigate the system 1/f noise and systematics, we plan to use continuous rotating half-wave plates (HWPs) as a polarization modulator at each aperture of two telescopes. One of the telescopes, called a low frequency telescope (LFT), covers the frequency range from 34 to 270 GHz, requiring the HWP to have a high modulation efficiency in the wide bandwidth. We employ a Pancharatnam-type achromatic HWP (AHWP) to achieve the broadband coverage. The AHWP consists of nine layer stacked HWPs with the optic axes mutually rotated by the angles optimized for the LFT bandwidth. In this paper, we report our development status of the nine layer AHWP and measurement results on the modulation efficiency and the phase as a function of frequency.

The Simons Observatory (SO) will observe the temperature and polarization anisotropies of the cosmic microwave background (CMB) over a wide range of frequencies (27 to 270 GHz) and angular scales by using both small (∼0.5 m) and large (∼6 m) aperture telescopes. The SO small aperture telescopes will target degree angular scales where the primordial B-mode polarization signal is expected to peak. The incoming polarization signal of the small aperture telescopes will be modulated by a cryogenic, continuously-rotating half-wave plate (CRHWP) to mitigate systematic effects arising from slowly varying noise and detector pair-differencing. In this paper, we present an assessment of some systematic effects arising from using a CRHWP in the SO small aperture systems. We focus on systematic effects associated with structural properties of the HWP and effects arising when operating a HWP, including the amplitude of the HWP synchronous signal (HWPSS), and I → P (intensity to polarization) leakage that arises from detector non-linearity in the presence of a large HWPSS. We demonstrate our ability to simulate the impact of the aforementioned systematic effects in the time domain. This important step will inform mitigation strategies and design decisions to ensure that SO will meet its science goals.

Polarization modulation using a continuously rotating half-wave plate (HWP) is a promising technique to reduce both low-frequency noise and instrumental systematics for Cosmic Microwave Background (CMB) polarization measurements targeting in ationary B-modes. Although a HWP is best placed sky-side of the telescope optics in order to minimize systematics, >0.5 meter aperture class telescopes must put the HWP elsewhere in the optics chain due to current fabrication limitations in the available HWP size. Polarbear is a ground-based CMB experiment installed on the 2.5m aperture off-axis Gregorian-Dragone type Huan Tran Telescope (HTT) designed to satisfy the Mizuguchi-Dragone condition. Polarbear-2 is a receiver that will be installed on a second HTT in 2018. Polarbear-2 is designed to have a larger field-of-view (FOV) and vastly increased sensitivity to the polarized CMB compared to Polarbear. From the third season of observations, Polarbear has installed a continuously rotating HWP at the spatially localized focus plane between the HTT primary and secondary re ectors which is an optimal location for minimizing the HWP diameter. The HWP's polarization angle re ection with respect to its birefringent axis will theoretically break the Mizuguchi-Dragone condition when placed between the two reflectors and increase cross-polarization systematics. In this study, we analyze how the Mizuguchi-Dragone condition is violated due to a HWP at this location. We then estimate the crosspolarization systematics of the HTT using physical optics simulations. We model an ideal HWP at various angles to estimate the effects of demodulation. We evaluate the increased cross-polarization as the Stokes Q-U mixing term using the Mueller Matrix formalism. It is calculated that this term creates a varying dipole beam pattern whose amplitude ranges from 1% at the center to 10% at the edge FOV pixels for Polarbear and potentially up to 20% for Polarbear-2. We also estimate the leakage of the E-mode into the B-mode angular power spectrum measurements due to this cross-polarization. We show that the cross-polarization systematic error leakage is sufficiently lower than the Polarbear-2 statistical uncertainty thanks to mitigations such as focal plane averaging and sky rotation. Currently for Polarbear-2 we are planning to place the HWP at Gregorian focus, but keeping the HWP at prime focus as a back-up solution in case that there are unforeseen telescope spatial and HWP material size constraints. Through this study we find that even though a HWP between the two reflectors will violate the Mizuguchi-Dragone condition, this HWP at prime focus will still have sufficiently low cross-polarization for Polarbear-2. The prime focus HWP is a potential configuration that can be applied to similar off-axis Gregorian-Dragone telescopes in order to minimize the required HWP diameter.

The sensitivity requirements of modern CMB instruments place high demands on the use of low loss materials for filter, lens and window devices. Anti-reflection coating (ARC) designs are routinely used to effect minimal dielectric fringing over a limited waveband, however there is a need to maximize this bandwidth over the operating range of the instrument. Here we present the design, manufacture and testing of prototype polypropylene devices based on multiple layer ARCs, to effect high transmission over three octaves of frequency.

The Simons Observatory (SO) will measure the cosmic microwave background (CMB) in both temperature and polarization over a wide range of angular scales and frequencies from 27-270 GHz with unprecedented sensitivity. One technology for coupling light onto the ~50 detector wafers that SO will field is spline-profiled feedhorns, which offer tunability between coupling efficiency and control of beam polarization leakage effects. We will present efforts to scale up feedhorn production for SO and their viability for future CMB experiments, including direct-machining metal feedhorn arrays and laser machining stacked Si arrays.

Publisher's Note: This paper, originally published on, 9 July 2018, was replaced with a corrected/revised version on,12 September 2023. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance.