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- Front Matter: Volume 7736
- Project Status I
- New AO System Designs I
- Modeling, Analysis, and Simulation Tools I
- Project Status II
- New AO System Designs II
- Modeling, Analysis, and Simulation Tools II
- Wavefront Sensors I
- Real-Time Control I
- Modeling, Analysis, and Simulation Tools III
- Quantitative Astronomy
- Exoplanet Instruments
- New AO System Designs III
- Laser Systems
- Atmospheric Characterization
- Innovative AO Concepts
- Wavefront Sensors II
- Wavefront Correctors
- Real-Time Control II
- Poster Sessions
Front Matter: Volume 7736
Front Matter: Volume 7736
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 7736, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.
Project Status I
The scientific impact of reaching the diffraction limit with ELTs
Show abstract
The new generation of extremely large telescopes (ELTs) will have key advantages over today's 8-10m telescopes. They
will collect more light due to their larger area: light-gathering power scales as the telescope diameter D2, so gains of a
factor of ~10 or more are expected. Further, with adaptive optics performing at close to the diffraction limit, ELTs will
have much higher point-source sensitivity. This is because for observations limited by background light from the sky,
there will be less background included within a diffraction-limited area. Point-source sensitivity will improve at least as
fast as D4, permitting gains of a factor of 70 - 100. We describe a few of the areas of astronomical science which stand to
benefit from these huge performance improvements: 1) Direct imaging and spectroscopy of giant extrasolar planets, and
of protoplanetary disks. 2) Resolved stellar populations and in particular the kinematics of stars close to the black hole at
the Galactic Center, and 3) Properties of galaxies at redshifts from 1.5 to 7, to shed new light on the processes of galaxy
assembly and evolution. These and other new science capabilities will enable ELTs to produce dramatic advances in
astrophysical understanding.
First light adaptive optics systems and components for the Thirty Meter Telescope
Show abstract
Adaptive optics (AO) is essential for many elements of the science case for the Thirty Meter Telescope (TMT). The
initial requirements for the observatory's facility AO system include diffraction-limited performance in the near IR, with
50 per cent sky coverage at the galactic pole. Point spread function uniformity and stability over a 30 arc sec field-ofview
are also required for precision photometry and astrometry. These capabilities will be achieved via an order 60×60
multi-conjugate AO system (NFIRAOS) with two deformable mirrors, six laser guide star wavefront sensors, and three
low-order, IR, natural guide star wavefront sensors within each client instrument. The associated laser guide star facility
(LGSF) will employ 150W of laser power at a wavelength of 589 nm to generate the six laser guide stars.
We provide an update on the progress in designing, modeling, and validating these systems and their components over
the last two years. This includes work on the layouts and detailed designs of NFIRAOS and the LGSF; fabrication and
test of a full-scale prototype tip/tilt stage (TTS); Conceptual Designs Studies for the real time controller (RTC) hardware
and algorithms; fabrication and test of the detectors for the
laser- and natural-guide star wavefront sensors; AO system
modeling and performance optimization; lab tests of wavefront sensing algorithms for use with elongated laser guide
stars; and high resolution LIDAR measurements of the mesospheric sodium layer. Further details may be found in
specific papers on each of these topics.
The Magellan Telescope Adaptive Secondary AO System: a visible and mid-IR AO facility
Show abstract
The Magellan Clay telescope is a 6.5m Gregorian telescope located in Chile at Las Campanas Observatory.
The Gregorian design allows for an adaptive secondary mirror that can be tested off-sky in a straightforward
manner. We have fabricated a 85 cm diameter aspheric adaptive secondary with our subcontractors
and partners, the ASM passed acceptance tests in July 2010. This secondary has 585 actuators with <1
msec response times (0.7 ms typically). This adaptive secondary will allow low emissivity AO science. We
will achieve very high Strehls (~98%) in the Mid-IR (3-26 microns) with the BLINC/MIRAC4 Mid-IR
science camera. This will allow the first "super-resolution" and nulling Mid-IR studies of dusty southern
objects. We will employ a high order (585 mode) pyramid wavefront sensor similar to that now
successfully used at the Large Binocular Telescope. The relatively high actuator count will allow modest
Strehls to be obtained in the visible (0.63-1.05 μm). Moderate (~20%) Strehls have already been obtained
at 0.8 μm at the LBT with the same powerful combination of a next generation ASM and Pyramid WFS as
we are providing for Magellan. Our visible light AO (VisAO) science camera is fed by an advanced triplet
ADC and is piggy-backed on the WFS optical board. We have designed an additional "clean-up" very fast
(2 kHz) tilt stabilization system for VisAO. Also a high-speed shutter will be used to block periods of poor
correction. The VisAO facility can be reconfigured to feed an optical IFU spectrograph with 20 mas
spaxels. The entire system passed CDR in June 2009, and is
now finished the fabrication phase and is entering the
integration phase. The system science and performance
requirements, and an overview the design, interface and
schedule for the Magellan AO system are presented here.
The Gemini MCAO System GeMS: nearing the end of a lab-story
Show abstract
GeMS (the Gemini Multi-conjugated adaptive optics System) is a facility instrument for the Gemini-South
telescope. It will deliver a uniform, diffraction-limited image quality at near-infrared (NIR) wavelengths over an
extended FoV or more than 1 arcmin across. GeMS is a unique and challenging project from the technological
point of view and because of its control complexity. The system includes 5 laser guide stars, 3 natural guide
stars, 3 deformable mirrors optically conjugated at 0, 4.5 and 9km and 1 tip-tilt mirror. After 10 years since
the beginning of the project, GeMS is finally reaching a state in which all the subsystems have been received,
integrated and, in the large part, tested. In this paper, we report on the progress and current status of the
different sub-systems with a particular emphasis on the calibrations, control and optimization of the AO bench.
Latest achievements of the MCAO testbed for the GREGOR Solar Telescope
Show abstract
The testbed of the MCAO for the new 1.5 meter solar telescope GREGOR is now operational. Most of the
components will be moved to the telescope after commissioning. The testbed features 4 adaptive mirrors (1 tiptilt,
and 3 DMs), and two Hartmann-Shack sensor units for wavefront tomography in a guide-region oriented
approach. First system characteristics gained from setting up operation of the testbed are presented. We
also comment on the effect of high-altitude deformable mirrors on subaperture alignment, and misregistration.
We conclude that on-axis wavefront sensors should not be located behind high-altitude deformable mirrors.
Furthermore, we present a general opto-geometric characteristic of micro-lens arrays needed for a
Hartmann-Shack sensor which shall be used for extended fields of view - be it solar surface or laser guide stars, for example.
This characteristic can be useful to have custom-made arrays manufactured for reasonable prices.
The adaptive optics and wavefront correction systems for the Advanced Technology Solar Telescope
Show abstract
The high order adaptive optics (HOAO) system is the centerpiece of the ATST wavefront correction system. The ATST
wavefront correction system is required to achieve a Strehl of
S = 0.6 or better at visible wavelength. The system design
closely follows the successful HOAO implementation at the Dunn Solar Telescope and is based on the correlating
Shack-Hartmann wavefront sensor. In addition to HOAO the ATST will utilize wavefront sensors to implement active
optics (aO) and Quasi Static Alignment (QSA) of the telescope optics, which includes several off-axis elements.
Provisions for implementation of Multi-conjugate adaptive optics have been made with the design of the optical path that
feeds the instrumentation at the coudé station. We will give an overview of the design of individual subsystems of the
ATST wavefront correction system and describe some of the unique features of the ATST wavefront correction system,
such as the need for thermally controlled corrective elements.
First light AO (FLAO) system for LBT: final integration, acceptance test in Europe, and preliminary on-sky commissioning results
Show abstract
In this paper we present the laboratory characterization and performance evaluation of the First Light Adaptive
Optics (FLAO) the Natural Guide Star adaptive optics system for the Large Binocular Telescope (LBT). The
system uses an adaptive secondary mirror with 672 actuators and a pyramid wavefront sensor with adjustable
sampling of the telescope pupil from 30×30 down to 4×4 subapertures. The system was fully assembled in the
Arcetri Observatory laboratories, passing the acceptance test in December 2009. The performance measured
during the test were closed to goal specifications for all star magnitudes. In particular FLAO obtained 83%
Strehl Ratio (SR) in the bright end (8.5 magnitudes star in R band) using H band filter and correcting 495
modes with 30×30 subapertures sampling. In the faint end (16.4 magnitude) a 5.0% SR correcting 36 modes
with 7×7 subapertures was measured. The seeing conditions for these tests were 0.8" (r0 = 0.14m @ 550 nm)
and an average wind speed of 15m/s. The results at other seeing conditions up to 1.5" are also presented. The
system has been shipped to the LBT site, and the commissioning is taking place since March to December 2010.
A few on sky results are presented.
New AO System Designs I
Scientific potential of ground layer adaptive optics on large telescopes
Show abstract
Ground-layer Adaptive Optics offers a unique approach to enhancing the power of large telescopes to explore a wide
range of astrophysical phenomena. By accessing wide fields of view with image concentrations that are significantly
improved over natural seeing, ground-layer AO systems can probe stellar populations in crowded and confused regions
of the Milky Way and nearby galaxies, probe the internal dynamics of large samples of galaxies in the distant universe
and provide a cost effective path towards highly multiplexed observations of large samples. The improved image
concentration over large fields of view offered by ground-layer AO will allow significant gains in sensitivity for multiobject
spectrographs operating in the near-IR. This will lead to improved understanding of the formation of the first
galaxies and stars as well as the evolution of massive galaxies when the Universe was a few billion years old. Groundlayer
AO systems have the potential to eliminate poor seeing from most astronomical sites and to improve the
productivity of large and extremely large telescopes.
NFIRAOS: TMT's facility adaptive optics system
Show abstract
NFIRAOS, the TMT Observatory's initial facility AO system is a
multi-conjugate AO system feeding science light from
0.8 to 2.5 microns wavelength to several near-IR client instruments. NFIRAOS has two deformable mirrors optically
conjugated to 0 and 11.2 km, and will correct atmospheric turbulence with 50 per cent sky coverage at the galactic pole.
An important requirement is to have very low background: the plan is to cool the optics; and one DM is on a tip/tilt stage
to reduce surface count. NFIRAOS' real time control uses multiple sodium laser wavefront sensors and up to three IR
natural guide star tip/tilt and/or tip/tilt/focus sensors located within each client instrument. Extremely large telescopes
are sensitive to errors due to the variability of the sodium layer. To reduce this sensitivity, NFIRAOS uses innovative
algorithms coupled with Truth wavefront sensors to monitor a natural star at low bandwidth. It also includes an IR acquisition
camera, and a high speed NGS WFS for operation without lasers. For calibration, NFIRAOS includes simulators
of both natural stars at infinity and laser guide stars at varying range distance. Because astrometry is an important
science programme for NFIRAOS, there is a precision pinhole mask deployable at the input focal plane. This mask is
illuminated by a science wavelength and flat-field calibrator that shines light into NFIRAOS' entrance window. We
report on recent effort especially including trade studies to reduce field distortion in the science path and to reduce cost
and complexity.
The GMT adaptive optics system
Show abstract
The design of the adaptive optics (AO) system for the GMT is currently being developed. The baseline system is
planned around a segmented adaptive secondary mirror (ASM), with elements similar in size to current ASM's for 8 m
telescopes. A facility wavefront sensing system is planned to provide AO correction at several science instrument ports.
The AO system will contain a subsystem dedicated to controlling the relative phases between the seven segments of the
GMT aperture. The anticipated modes include natural guide star, laser tomography, and ground layer adaptive optics. A
cooled optical relay is described to provide baffling and reimaging of the focal plane to the various science ports. The
laser projection system will use six beacons on an adjustable radius to support both diffraction-limited and ground layer
correction modes. Modeling work, as well as science instrument design development will be integrated with this design
effort to develop a concept that provides efficient diffraction-limited performance and seeing-improved capabilities for
the GMT.
ATLAS: the E-ELT laser tomographic adaptive optics system
Show abstract
ATLAS is a generic Laser Tomographic AO (LTAO) system for the E-ELT. Based on modular, relatively simple, and
yet innovative concepts, it aims at providing diffraction limited images in the near infra-red for a close to 100 percent
sky coverage.
ARGOS: the laser guide star system for the LBT
Show abstract
ARGOS is the Laser Guide Star adaptive optics system for the Large Binocular Telescope. Aiming for a wide field
adaptive optics correction, ARGOS will equip both sides of LBT with a multi laser beacon system and corresponding
wavefront sensors, driving LBT's adaptive secondary mirrors. Utilizing high power pulsed green lasers the artificial
beacons are generated via Rayleigh scattering in earth's atmosphere. ARGOS will project a set of three guide stars above
each of LBT's mirrors in a wide constellation. The returning scattered light, sensitive particular to the turbulence close to
ground, is detected in a gated wavefront sensor system. Measuring and correcting the ground layers of the optical
distortions enables ARGOS to achieve a correction over a very wide field of view. Taking advantage of this wide field
correction, the science that can be done with the multi object spectrographs LUCIFER will be boosted by higher spatial
resolution and strongly enhanced flux for spectroscopy. Apart from the wide field correction ARGOS delivers in its
ground layer mode, we foresee a diffraction limited operation with a hybrid Sodium laser Rayleigh beacon combination.
SAXO, the eXtreme Adaptive Optics System of SPHERE: overview and calibration procedure
Show abstract
The direct imaging of exoplanet is a challenging goal of todays astronomy. The light transmitted by exoplanet
atmosphere is of a great interest as it may witness for life sign. SPHERE is a second generation instrument for
the VLT, dedicated to exoplanet imaging, detection, and characterisation. SPHERE is a global project of an
European consortium of 11 institutes from 5 countries. We present here the state of the art of the AIT of the
Adaptive Optics part of the instrument. In addition we present fine calibration procedures dedicated to eXtreme
Adaptive Optics systems. First we emphasized on vibration and turbulence identification for optimization of the
control law. Then, we describe a procedure able to measure and compensate for NCPA with a coronagraphic
system.
Modeling, Analysis, and Simulation Tools I
Impact of laser guide star fratricide on TMT MCAO system
Show abstract
Laser beams projected from the ground to form laser guide stars (LGS) experience scattering and absorption
that reduce their intensity as they propagate through the atmosphere. Some fraction of the scattered light will
be collected by the other LGS wavefront sensors and causes additional background in parts of the pupil. This
cross-talk is referred to as the fratricide effect. In this paper we quantify the magnitude of four different sources
of scattering/absorption and back scattering, and evaluate their impact on performance with various zenith
angles and turbulence profiles for the Thirty Meter Telescope (TMT) MCAO system, NFIRAOS. The resulting
wavefront error is on the order of 5 to 20 nm RMS, provided that the mean background from the fratricide can
be calibrated and subtracted with an accuracy of 80%. We have also found that the impact of fratricide is a
weak function of LGS asterism radius.
Monte-Carlo simulation of ELT scale multi-conjugate and multi-object AO systems
Show abstract
The use of software based simulation packages is essential for the design of adaptive optics systems on next
generation ELT scale telescopes. We present Monte-Carlo AO simulation results for an E-ELT multi-IFU spectrograph
instrument comprising multiple laser and natural guide stars with wavefront correction along multiple
lines of sight. We discuss the techniques used to perform these simulations. Considerations are also given to
compressed reconstructor representations which can greatly simplify the design of real-time control systems. We
also discuss work on the use of GPUs for AO simulation.
Tomographic control for wide field AO systems on extremely large telescopes
Show abstract
We investigate in this article tomographic control using both Laser and Natural Guide Stars (LGS and NGS) in the
particular framework of the European Extremely Large Telescope
(E-ELT) Wide Field Adaptive Optics (WFAO)
modules design. A similar global control strategy has been indeed derived for both the Laser Tomographic Adaptive
Optics (LTAO) and Multi-Conjugate Adaptive Optics (MCAO) modules of the E-ELT, due to similar constraints. This
control strategy leads in both cases to a split control of low order modes measured thanks to NGS and high order modes
measured thanks to LGS. We investigate here this split tomographic control, compared to an optimal coupled solution.
To support our analysis, a dedicated simulation code has been developed. Indeed, due to the huge complexity of the EELT,
fast simulation tools must be considered to explore quickly the tomographic issues. We describe our control
strategy which has lead to considering split tomographic control. First results on Tomography for E-ELT WFAO systems
are then presented and discussed.
Impact of Cn2 profile structure on wide-field AO performance
Show abstract
WFAO systems are in their design phase for the ELTs. MCAO (MAORY), LTAO (ATLAS) and MOAO (EAGLE)
approaches have been analyzed for the E-ELT. All these approaches require a precise tomographic reconstruction of the
turbulent volume. In that frame, Cn2 profiles come up at two levels: the input "true" profile, and the prior profile used as
a regularization in the tomographic reconstruction. The impacts of the structure and the complexity of the Cn2 profile on
the residual error after tomographic reconstruction are analyzed and discussed. We show that isoplanatic angle is not
sufficient to characterize profiles in WFAO. We highlight the importance of a well sampled Cn2 input profile and prior
profile to be considered in the tomographic reconstructor.
Project Status II
W. M. Keck Observatory's next-generation adaptive optics facility
Show abstract
We report on the preliminary design of W.M. Keck Observatory's (WMKO's) next-generation adaptive optics (NGAO)
facility. This facility is designed to address key science questions including understanding the formation and evolution
of today's galaxies, measuring dark matter in our galaxy and beyond, testing the theory of general relativity in the
Galactic Center, understanding the formation of planetary systems around nearby stars, and exploring the origins of our
own solar system. The requirements derived from these science questions have resulted in NGAO being designed to
have near diffraction-limited performance in the near-IR (K-Strehl ~ 80%) over narrow fields (< 30" diameter) with
modest correction down to ~ 700 nm, high sky coverage, improved sensitivity and contrast and improved photometric
and astrometric accuracy. The resultant key design features include multi-laser tomography to measure the wavefront
and correct for the cone effect, open loop AO-corrected near-IR
tip-tilt sensors with MEMS deformable mirrors (DMs)
for high sky coverage, a high order MEMS DM for the correction of atmospheric and telescope static errors to support
high Strehls and high contrast companion sensitivity, point spread function (PSF) calibration to benefit quantitative
astronomy, a cooled science path to reduce thermal background, and a high-efficiency science instrument providing
imaging and integral field spectroscopy.
Manufacturing of the ESO adaptive optics facility
Show abstract
The ESO Adaptive Optics Facility (AOF) consists in an evolution of one of the ESO VLT unit telescopes to a laser
driven adaptive telescope with a deformable mirror in its optical train, in this case the secondary 1.1m mirror, and four
Laser Guide Stars (LGSs). This evolution implements many challenging technologies like the Deformable Secondary
Mirror (DSM) including a thin shell mirror (1.1 m diameter and 2mm thin), the high power Na lasers (20W), the low
Read-Out Noise (RON) WaveFront Sensor (WFS) camera (< 1e-) and SPARTA the new generation of Real Time
Computers (RTC) for adaptive control. It also faces many problematic similar to any Extremely Large Telescope (ELT)
and as such, will validate many technologies and solutions needed for the European ELT (E-ELT) 42m telescope. The
AOF will offer a very large (7 arcmin) Field Of View (FOV) GLAO correction in J, H and K bands (GRAAL+Hawk-I),
a visible integral field spectrograph with a 1 arcmin GLAO corrected FOV (GALACSI-MUSE WFM) and finally a
LTAO 7.5" FOV (GALACSI-MUSE NFM). Most systems of the AOF have completed final design and are in
manufacturing phase. Specific activities are linked to the modification of the 8m telescope in order to accommodate the
new DSM and the 4 LGS Units assembled on its Center-Piece. A one year test period in Europe is planned to test and
validate all modes and their performance followed by a commissioning phase in Paranal scheduled for 2014.
E-ELT M5 field stabilisation unit scale 1 demonstrator design and performances evaluation
J. M. Casalta,
J. Barriga,
J. Ariño,
et al.
Show abstract
The M5 Field stabilization Unit (M5FU) for European Extremely Large Telescope (E-ELT) is a fast correcting optical
system that shall provide tip-tilt corrections for the telescope dynamic pointing errors and the effect of atmospheric tiptilt
and wind disturbances.
A M5FU scale 1 demonstrator (M5FU1D) is being built to assess the feasibility of the key elements (actuators, sensors,
mirror, mirror interfaces) and the real-time control algorithm. The strict constraints (e.g. tip-tilt control frequency range
100Hz, 3m ellipse mirror size, mirror first Eigen frequency 300Hz, maximum tip/tilt range ± 30 arcsec, maximum tiptilt
error < 40 marcsec) have been a big challenge for developing the M5FU Conceptual Design and its scale 1
demonstrator.
The paper summarises the proposed design for the final unit and demonstrator and the measured performances
compared to the applicable specifications.
Commissioning status of Subaru laser guide star adaptive optics system
Show abstract
The current status of commissioning and recent results in performance of Subaru laser guide star adaptive optics
system is presented. After the first light using natural guide stars with limited configuration of the system in
October 2006, we concentrated to complete a final configuration for a natural guide star to serve AO188 to an
open use observation. On sky test with full configurations using natural guide star started in August 2008, and
opened to a public one month later. We continuously achieved around 0.6 to 0.7 of Strehl ratio at K band using
a bright guide star around 9th to 10th magnitude in R band. We found an unexpectedly large wavefront error
in our laser launching telescope. The modification to fix this large wavefront error was made and we resumed
the characterization of a laser guide star in February 2009. Finally we obtained a round-shaped laser guide star,
whose image size is about 1.2 to 1.6 arcsec under the typical seeing condition. We are in the final phase of
commissioning. A diffraction limited image by our AO system using a laser guide star will be obtained in the
end of 2010. An open use observation with laser guide star system will start in the middle of 2011.
Status of the 6.5m MMT Telescope laser adaptive optics system
Show abstract
The Laser Adaptive Optics system of the 6.5 m MMT telescope has now been commissioned with Ground Layer
Adaptive Optics operations as a tool for astronomical science. In this mode the wavefronts sampled by each of five laser
beacons are averaged, leading to an estimate of the aberration in the ground layer. The ground layer is then compensated
by the deformable secondary mirror at 400 Hz. Image quality of
0.2-0.3 arc sec is delivered in the near infrared bands
from 1.2-2.5 μm over a field of view of 2 arc minutes. Tomographic wavefront sensing tests in May 2010 produced open
loop data necessary to streamline the software to generate a Laser Tomography Adaptive Optics (LTAO) reconstructor.
In addition, we present the work being done to achieve optimal control PID wavefront control and thus increase the
disturbance rejection frequency response for the system. Finally, we briefly describe plans to mount the ARIES near
infrared imager and echelle spectrograph, which will support the 2 arc min ground-layer corrected field and will exploit
the diffraction limit anticipated with LTAO.
Status update of the CANARY on-sky MOAO demonstrator
Show abstract
The CANARY on-sky MOAO demonstrator is being integrated in the laboratory and a status update about its
various components is presented here. We also discuss the alignment and calibration procedures used to improve
system performance and overall stability. CANARY will be commissioned at the William Herschel Telescope at
the end of September 2010.
New AO System Designs II
Conceptual design and performance of the multiconjugate adaptive optics module for the European Extremely Large Telescope
Show abstract
The Multi-conjugate Adaptive Optics RelaY (MAORY) for the European Extremely Large Telescope (E-ELT) provides
a corrected field of view of up to 2 arcmin diameter over the wavelength range 0.8-2.4 μm. It is expected to achieve a
correction of high quality and uniformity with high sky coverage: with a seeing of 0.8 arcsec in the visible, the expected
Strehl Ratio averaged over a 1 arcmin field is approximately 50% at 2.16 μm wavelength over 50% of the sky at the
Galactic Pole. Wavefront correction is obtained by means of the E-ELT adaptive mirrors M4/M5 and of two post-focal
deformable mirrors conjugated at 4km and 12.7km from the telescope pupil. Wavefront sensing is performed by 6
Sodium laser guide stars and by 3 natural guide stars, used to measure atmospheric and windshake tilt and to provide a
reference for the focus and for the low-order aberrations induced by the Sodium layer. MAORY is located on the E-ELT
Nasmyth platform and has a gravity invariant port, feeding the high angular resolution camera MICADO, and a lateral
port for a detached instrument as the infrared spectrograph SIMPLE.
EAGLE MOAO system conceptual design and related technologies
Show abstract
EAGLE is the multi-object spatially-resolved near-IR spectrograph instrument concept for the E-ELT, relying
on a distributed Adaptive Optics, so-called Multi Object Adaptive Optics. This paper presents the results of
a phase A study. Using 84×84 actuator deformable mirrors, the performed analysis demonstrates that 6 laser
guide stars (on an outer ring of 7.2' diameter) and up to 5 natural guide stars of magnitude R < 17, picked-up in
a 7.3' diameter patrol field of view, allow us to obtain an overall performance in terms of Ensquared Energy of
35% in a 75×75mas2 resolution element at H band whatever the target direction in the centred 5' science field
for median seeing conditions. In terms of sky coverage, the probability to find the 5 natural guide stars is close
to 90% at galactic latitudes |b| ~ 60 deg. Several MOAO demonstration activities are also on-going.
Raven: a harbinger of multi-object adaptive optics-based instruments at the Subaru Telescope
Show abstract
In the context of instrumentation for Extremely Large Telescopes (ELTs), an Integral Field Spectrographs
(IFSs), fed with a Multi-Object Adaptive Optics (MOAO) system, has many scientific and technical advantages.
Integrated with an ELT, a MOAO system will allow the simultaneous observation of up to 20 targets in a several
arc-minute field-of-view, each target being viewed with unprecedented sensitivity and resolution. However,
before building a MOAO instrument for an ELT, several critical issues, such as open-loop control and calibration,
must be solved. The Adaptive Optics Laboratory of the University of Victoria, in collaboration with the Herzberg
Institute of Astrophysics, the Subaru telescope and two industrial partners, is starting the construction of a
MOAO pathfinder, called Raven. The goal of Raven is two-fold: first, Raven has to demonstrate that MOAO
technical challenges can be solved and implemented reliably for routine on-sky observations. Secondly, Raven
must demonstrate that reliable science can be delivered with multiplexed AO systems. In order to achieve these
goals, the Raven science channels will be coupled to the Subaru's spectrograph (IRCS) on the infrared Nasmyth
platform. This paper will present the status of the project, including the conceptual instrument design and a
discussion of the science program.
Adaptive optics and MCAO for the 4-m European Solar Telescope EST
Show abstract
A consortium of more than 20 European solar physics institution from 15 different countries is conducting a design
study for a 4 m class solar telescope which shall be situated at the Canary Islands. In this paper we introduce the AO and
MCAO design concept for EST. A ground layer deformable mirror is combined with an arrangement of four deformable
layer mirrors. A combination of Shack-Hartmann wave front sensors with wide and narrow fields of view is used to
control the system and to achieve a corrected field of view of one arcmin.
Modeling, Analysis, and Simulation Tools II
Laser guide star return flux simulations based on observed sodium density profiles
Show abstract
We extend previous sodium LGS models by integrating the return flux across the mesosphere, taking into account
variable mesospheric gas density, temperature, and local sodium density. This method allows us to produce accurate
predictions of the actual return flux on the ground, relevant for determining the performance of adaptive-opticsassisted
instruments. We find that the flux distribution across the sky depends strongly on geographic location and
laser parameters. Almost independent of location, future sodium LGS will be about three times brighter at zenith
than at the observing horizon.
Modeling update for the Thirty Meter Telescope laser guide star dual-conjugate adaptive optics system
Show abstract
This paper describes the modeling efforts undertaken in the past couple of years to derive wavefront error (WFE)
performance estimates for the Narrow Field Infrared Adaptive Optics System (NFIRAOS), which is the facility
laser guide star (LGS) dual-conjugate adaptive optics (AO) system for the Thirty Meter Telescope (TMT). The
estimates describe the expected performance of NFIRAOS as a function of seeing on Mauna Kea, zenith angle,
and galactic latitude (GL). They have been developed through a combination of integrated AO simulations, side
analyses, allocations, lab and lidar experiments.
Fractal iterative method for fast atmospheric tomography on extremely large telescopes
Show abstract
A challenge of adaptive optics (AO) on Extremely Large Telescopes (ELTs) is to overcome the difficulty of solving a huge
number of equations in real time, especially when atmospheric tomography is involved. This is particularly the case for
multi-conjugate or multi-objects AO systems. In addition, the quality of the wavefront estimation is crucial to optimize the
performances of the future systems in a situation where measurements are missing and noises are correlated.
The Fractal Iterative Method has been introduced as a fast iterative algorithm for minimum variance wavefront reconstruction
and control on ELTs. This method has been successfully tested on Classical Single Conjugate AO systems on
Octopus numerical simulator at ESO. But the minimum variance approach is expected to be mostly useful with atmospheric
tomography.
We present the first results obtained with FrIM in the context of atmospheric tomography. We recall the principle of
the algorithm and we summarize the formalism used for modeling the measurements obtained from laser guide stars that
entail spot elongation and tip/tilt indetermination, mixed with low order measurements from natural guide stars. We show
the respective effects of tip/tilt indetermination, spot elongation, unseen modes on various configurations, as well as the
usefulness of priors and correct noise models in the reconstruction.
This analysis is essential for balancing the various errors that combine in a quite complex way and to optimize the
configuration of the future AO systems for specific science cases and instrument requirements.
The hunt for 100% sky coverage
Show abstract
Tomographic AO (or Wide Field AO) systems use LGS to build a 3D model of turbulence, but rely on NGS for
low order sensing. .To preserve reasonable sky coverage, each photon coming from the NGS to sense Tip Tilt has
to be optimally exploited. That means a smart control law, a low detection noise, a concentration of the photons
onto a small patch and a wave front sensor concept with favorable noise propagation. In this paper, we describe
the system choices that were made during the E-ELT laser tomographic system ATLAS phase A study, in order
to get a sky coverage as close as possible to 100%. A correct estimation of the sky coverage is therefore a key
issue. We have developped a sky coverage estimation strategy based on a Besan¸con model starfield generation,
a star(s) selection tool, and a careful estimation of the residual anisoplanatism (after reconstruction process
between the NGSs), noise and temporal contributors. We describe the details of the procedure, and derive the
ATLAS expected performance.
Wavefront Sensors I
Characterization of OCam and CCD220: the fastest and most sensitive camera to date for AO wavefront sensing
Show abstract
For the first time, sub-electron read noise has been achieved with a camera suitable for astronomical wavefront-sensing
(WFS) applications. The OCam system has demonstrated this performance at 1300 Hz frame rate and with
240×240-pixel frame rate.
ESO and JRA2 OPTICON2 have jointly funded e2v technologies to develop a custom CCD for Adaptive Optics (AO)
wavefront sensing applications. The device, called CCD220, is a compact Peltier-cooled 240×240 pixel frame-transfer
8-output back-illuminated sensor using the EMCCD technology. This paper demonstrates sub-electron read noise at
frame rates from 25 Hz to 1300 Hz and dark current lower than 0.01
e-/pixel/frame. It reports on the comprehensive,
quantitative performance characterization of OCam and the CCD220 such as readout noise, dark current, multiplication
gain, quantum efficiency, charge transfer efficiency... OCam includes a low noise preamplifier stage, a digital board to
generate the clocks and a microcontroller. The data acquisition system includes a user friendly timer file editor to
generate any type of clocking scheme. A second version of OCam, called OCam2, was designed offering enhanced
performances, a completely sealed camera package and an additional Peltier stage to facilitate operation on a telescope or
environmentally rugged applications. OCam2 offers two types of
built-in data link to the Real Time Computer: the
CameraLink industry standard interface and various fiber link options like the sFPDP interface. OCam2 includes also a
modified mechanical design to ease the integration of microlens arrays for use of this camera in all types of wavefront
sensing AO system. The front cover of OCam2 can be customized to include a microlens exchange mechanism.
Adaptive optics wavefront sensors based on photon-counting detector arrays
Show abstract
For adaptive optics systems, there is a growing demand for wavefront sensors that operate at higher frame rates and with
more pixels while maintaining low readout noise. Lincoln Laboratory has been investigating Geiger-mode avalanche
photodiode arrays integrated with CMOS readout circuits as a potential solution. This type of sensor counts photons
digitally within the pixel, enabling data to be read out at high rates without the penalty of readout noise. After a brief
overview of adaptive optics sensor development at Lincoln Laboratory, we will present the status of silicon Geigermode-
APD technology along with future plans to improve performance.
A focal plane sensor for low-order sensing on laser tomographic systems: LIFT
Show abstract
Laser Tomographic systems, such as ATLAS, will rely on natural guide stars (NGS) to sense low order perturbation.
This low order perturbation contains low order turbulence and Telescope Windshake, which strength
lead to NGS wave front sensor (WFS) frame rate of several hundred Hertz. Therefore, the ability of the NGS
WFS to deliver precise low order measurements in low signal to noise conditions will drive the limit magnitude
of the NGS, hence the sky coverage. We have investigated the use of a focal plane sensor for this purpose, and
consider it as the most efficient sensor in this context. We propose LIFT (LInearized Focal-plane Technique),
and compare it to classical sensors, such as Quad Cell WFS, Pyramid WFS and Shack-Hartmann WFS. We
derive an analytic model of the noise propagation law, which we validate on End-to-End diffractive simulations,
based on realistic phase screens.
The Subaru Coronographic Extreme AO (SCExAO) system: implementation and performances of the Coronographic Low Order WaveFront Sensor
Show abstract
The Subaru Coronagraphic Extreme AO project (SCExAO) is a high performance coronagraph designed to
deliver high contrast at small angular separation. For the detection of structures near the diffraction limit, an
accurate control of low order wavefront aberrations - tip-tilt and focus - is essential as these aberrations create
light leaks that are the source of confusion in the final science image. To address this major difficulty, we have
equipped SCExAO with a specially designed Coronagraphic Low Order WaveFront Sensor (CLOWFS) using
defocused images of a reflective ring located in the focal plane, that can track tip-tilt errors as small as 10-3λ/D.
CLOWFS was originally designed to drive actuators in a closed-loop. Here, we show that it can also be used in
post-processing to efficiently subtract the tip-tilt induced coronagraphic leaks in the final science image.
Real-Time Control I
Advances in real-time control algorithms
Show abstract
Since the early days, many aspects of Adaptive Optics (AO) have seen tremendous changes. From the early
experimental systems providing low order correction in a tiny patch of sky to todays fully automated specialized
system offering correction in a much wider field and/or a much higher degree of correction, the evolution has
been remarkable. For example, deformable mirror (DM) technology and wavefront sensing methods have been
constantly improved. As well, real-time control algorithms have been greatly refined. This paper will review the
different real-time control strategies that have been used with astronomical adaptive optics. They all have in
common the same objective, that is the derivation of an optimal command for the deformable mirror(s) in order
to get the least amount of residual optical aberrations in the science path. Most of the time, the real-time control
algorithm is split in two independent components, the first part performing the wavefront (spatial) reconstruction,
the second part performing the temporal control. With the advent of the extremely large telescopes (ELTs), as
well as new AO modalities requiring several DMs and wavefront sensors, performing both these tasks in an ever
shrinking glimpse of time is even more challenging. We will describe advanced fast and iterative reconstruction
methods recently proposed for next generation AO systems. We will show how these algorithms combined with
sparse matrices and parallel computing techniques meet the requirements of Extremely Large Telescope (ELT)
real time computers.
Optimal AO control with NGS/LGS wavefront sensors: the multirate case
Show abstract
We present the minimum variance control solution for an AO system featuring several NGS/LGS wavefront
sensors operating at different sampling rates. We show that the optimal solution is based on a non-stationary
Kalman filter. A simple sequential implementation is proposed, with one update equation per sensor. A stationary
suboptimal solution is also derived.
An optimized controller for ARGOS: using multiple wavefront sensor signals for homogeneous correction over the field
Show abstract
ARGOS is the ground layer adaptive optics system planned for the LBT. The goal of such a ground layer
adaptive optics system is to provide a maximum homogeneity of the point spread function over the full field of
view. Controllers for optimized correction with an adaptive optics system with guide star and science target at
different field angles are well known in the case of a single guide star. As ARGOS uses three laser guide stars and
one auxiliary natural guide star a weighting scheme is required to optimize the homogeneity using all available
information. Especially the tip and tilt modes measured by the one single off axis guide star and estimated
thereof over the field will need to be improved by incorporation of the laser measurements. I will present the
full scheme for an optimized controller for the ARGOS system. This controller uses the wavefront signals of
the three lasers to additionally reconstruct the lower atmosphere. Information on the higher atmosphere will be
provided by a DIMM-MASS instrument. The control scheme is tested analytically and the variation of the point
spread function is then measured over the full field.
Wavefront control algorithms for the Keck next-generation adaptive optics system
Show abstract
The Keck Next Generation Adaptive Optics (KNGAO) system promises to yield high-Strehl observations over a
wide range of science wavelengths from the optical through the infrared. We describe the algorithms proposed for a
Real-Time Controller (RTC) implemented in a massive parallel processor environment. These algorithms take
advantage of the Fourier domain to speed up processing and ensure minimum variance control that incorporates
prior as well as current data. We present the unique approach to the design that enables such a complex tomography
processor to scale more favorably with telescope aperture size than the more traditional RTC approaches.
Modeling and prediction of turbulence-induced wavefront distortions
Show abstract
In recent years various researchers have proposed an optimal control approach for the rejection of
turbulence-induced wavefront distortions in an AO system. The essential element in the design
of an optimal controller is the choice for the turbulence model, which predicts the turbulence to
compensate for the inherent delay in the AO control loop. In this paper various models as proposed
in literature are considered; ranging from first order temporal models to high-order full spatialtemporal
models. The various models are analyzed and the resulting 1-step ahead predictors are
derived. The performance of the predictors are compared for a von Kármán type of turbulence
with frozen flow propagation in and time-varying propagation directions.
Modeling, Analysis, and Simulation Tools III
Progress and prospects in AO simulation capabilities
Show abstract
In this paper, we present different methods of simulating AO systems, and show how these simulation tools have evolved in the last
years. The evolutions have been driven by new projects (like more complex MCAO systems) and new telescopes (especially ELTs).
These developments have been made in several directions: increasing simulation speed, complexity (more effects taken into account)
and integrating the latest developments in algorithms.
We will also discuss new directions in simulations, like new applications and new ways of estimating AO system performance.
Results from the laboratory demonstration of the nonlinear curvature wavefront sensor
Show abstract
In this paper we show why a non-linear curvature wavefront sensor (nlCWFS) is superior to both
Shack-Hartmann wavefront sensor (SHWFS) and conventional curvature wavefront sensor (cCWFS)
for sensing mV < 15 natural guide stars. We have developed an experimental setup aimed at
comparing the the rms wavefront error obtained with the nlCWFS and the SHWFS. We describe
our experimental setup and present results from the laboratory demonstration of the nlCWFS. The
non-linear approach builds on the successful curvature wavefront sensing concept. The wavefront
is reconstructed from the defocused pupil images using the
Gerchberg-Saxton (GS) phase diversity
algorithm. We compare results obtained from reconstructing the wavefront using a Shack-Hartmann
wavefront sensor (SHWFS) and a nlCWFS for a monochromatic source. We discuss approaches
to overcome non-linearity issues and discuss the challenge of using two WFSs in the same spatiotemporal
control regime and the implementation of the nlCWFS on the 6.5 m MMT.
Comparing centroiding methods for Shack-Hartmann wavefront sensing with laser guide stars on an ELT
Show abstract
In this paper we present the results of a study comparing the performance of various centroiding methods on
an extended spot. Various spot shapes, in good agreement with measurements of the Sodium layer density
profile are investigated. We compare the performance of
center-of-gravity (COG) based ad cross-correlation
(CC) based methods and the matched filter (MF) algorithm. While their performance are comparable in the
case of a Gaussian Sodium profile, we show that, above 15 to 20m
off-axis, substantial differences appear in the
case of a known non-Gaussian Sodium density profile. CC based and MF methods seem to have comparable or
better performance with various spot shapes while non-Gaussian shapes have dramatic impact on COG based
methods.
Active control of a large deformable mirror for future E-ELT
Show abstract
Increasing dimensions of ground based telescopes and adaptive optics needs for these instruments require wide
deformable mirrors with a high number of actuators to compensate the effects of the atmospheric turbulence on the wave
fronts. The new dimensions and characteristics of these deformable mirrors lead to the apparition of structural vibrations,
which may reduce the rejection band width of the adaptive optics control loop.
The aim of this paper is the study of the dynamic behavior of a
1-meter prototype of E-ELT's deformable mirror in order
to identify its eigenmodes and to propose some ways to control its vibrations. We first present the first eigenmodes of the
structure determined by both finite element analysis and experimental modal analysis. Then we present the frequency
response of the prototype to a tilt excitation to estimate the effects of its vibrations on the adaptive optics loop. Finally
we suggest a method to control the dynamics of the deformable mirror.
Deformable mirror models for open-loop adaptive optics using non-parametric estimation techniques
Show abstract
Open-loop adaptive optics is a technique in which the turbulent wavefront is measured before it hits the deformable
mirror for correction; therefore the correct control of the mirror in open-loop is key in achieving the expected level of
correction. In this paper, we present non-parametric estimation techniques to model deformable mirrors working in
open-loop. We have results with mirrors characterized by non-linear behavior: a Xinetics electrostrictive mirror and a
Boston Micromachines MEMS mirror. The inputs for these models are the wavefront corrections to apply to the mirror
and the outputs are the set of voltages to shape the mirror. We have performed experiments on both mirrors, achieving
Go-To errors relative to peak-to-peak wavefront excursion in the order of 1 % RMS for the Xinetics mirror and 3 %
RMS for the Boston mirror . These techniques are trained with interferometric data from the mirror under control;
therefore they do not depend on the physical parameters of the device.
Ῑmaka: a Lagrange invariant of ELTs
Show abstract
The IMAKA project is a ground layer corrected wide field visible imager proposed for CFHT. It consists of three
processes or components: The dome and local turbulence will be controlled by ventilation; the remaining ground layer
turbulence will be corrected by a GLAO system and the free atmosphere seeing will be locally reduced by using an
Orthogonal Transfer CCD to correct for tip-tilt within the isokinetic angle of field stars.
In designing the AO system, whether based on an adaptive secondary mirror or using pupil relay optics, it becomes
apparent that the conjugation of the deformable mirror is a difficult constraint to achieve given the large field. It turns
out this problem is not isolated to IMAKA, because the Lagrange Invariant for our project is in the same range as that of
EAGLE on the E-ELT for example. The effects of tilting the deformable mirror with respect to the pupil or
compensating for misconjugation of an adaptive secondary mirror using a tomographic reconstructor have been
investigated using Monte-Carlo simulation codes, including our code developed specifically for GLAO simulations.
We report on quantitative results from IMAKA simulations for a variety of realistic turbulence conditions for each
topical scheme, and allude to how these results are applicable to ELTs' adaptive optics.
Optimal method for exoplanet detection by spectral and angular differential imaging
Show abstract
In the context of the SPHERE planet finder project, we further develop and characterize a recently proposed
method for the efficient direct detection of exoplanets from the ground using spectral and angular differential
imaging. The method, called ANDROMEDA, combines images appropriately into "pseudo-data", then uses all
of them in a Maximum-Likelihood framework to estimate the position and flux of potential planets orbiting
the observed star. The method's performance is assessed on realistic simulations of images performed by the
SPHERE consortium, and it is applied to experimental data taken by the VLT/NAOS-CONICA instrument.
Adaptive optics point spread function reconstruction: lessons learned from on-sky experiment on Altair/Gemini and pathway for future systems
Show abstract
We present the results of an on-sky point spread function reconstruction (PSF-R) experiment for the Gemini
North telescope adaptive optics system, Altair, in the simplest mode, bright on-axis natural guise star. We
demonstrate that our PSF-R method does work for system performance diagnostic but suffers from hidden
telescope and system aberrations that are not accounted for in the model, making the reconstruction unsuccessful
for Altair, for now. We discuss the probable origin of the discrepancy. In the last section, we propose alternative
PSF-R methods for future multiple natural and laser guide stars systems.
Quantitative Astronomy
Dissecting galaxies with adaptive optics
Show abstract
We describe several projects addressing the growth of galaxies and massive black holes, for which adaptive optics
is mandatory to reach high spatial resolution but is also a challenge due to the lack of guide stars and long
integrations. In each case kinematics of the stars and gas, derived from integral field spectroscopy, plays a key
role. We explain why deconvolution is not an option, and that instead the PSF is used to convolve a physical
model to the required resolution. We discuss the level of detail with which the PSF needs to be known, and the
ways available to derive it. We explain how signal-to-noise can limit the resolution achievable and show there
are many science cases that require high, but not necessarily diffraction limited, resolution. Finally, we consider
what requirements astrometry and photometry place on adaptive optics performance and design.
Novel multi-frame approach to photometry of exoplanets
Show abstract
Although many methods have been proposed for the detection of exoplanets with adaptive optics, the problem of
measuring their brightness is relatively neglected. We propose a novel, reference-less technique, which we call "PDF
deconvolution", where the traditional 2-D image deconvolution is replaced by a 1-D time-series deconvolution. We
present examples of its excellent accuracy on real and simulated adaptive optics observations with 3-8m apertures.
Recent results and perspectives for precision astrometry and photometry with adaptive optics
Jessica R. Lu,
Andrea M. Ghez,
Sylvana Yelda,
et al.
Show abstract
Large ground-based telescopes equipped with adaptive optics (AO) systems have ushered in a new era of highresolution
infrared photometry and astrometry. Relative astrometric accuracies of <0.2 mas have already been
demonstrated from infrared images with spatial resolutions of 55-95 mas resolution over 10-20" fields of view.
Relative photometric accuracies of 3% and absolute photometric accuracies of 5%-20% are also possible. I will
review improvements and current limitations in astrometry and photometry with adaptive optics of crowded
stellar fields. These capabilities enable experiments such as measuring orbits for brown dwarfs and exoplanets,
studying our Galaxy's supermassive black hole and its environment, and identifying individual stars in young
star clusters, which can be used test the universality of the initial mass function.
Exoplanet imaging with LOCI processing: photometry and astrometry with the new SOSIE pipeline
Show abstract
The Angular, Simultaneous Spectral and Reference Star Differential Imaging techniques (ADI, SSDI and RSDI)
are currently the main observing approaches that are being used to pursue large-scale direct exoplanet imaging
surveys and will be a key component of next-generation high-contrast imaging instrument science. To allow
detection of faint planets, images from these observing techniques are combined in a way to retain the planet
flux while subtracting as much as possible the residual speckle noise. The LOCI algorithm is a very efficient way of
combining a set of reference images to subtract the noise of a given image. Although high contrast performances
have been achieved with ADI/SSDI/RSDI & LOCI, achieving high accuracy photometry and astrometry can
be a challenge, due to various biases coming mainly from the inevitable partial point source self-subtraction
for ADI/SSDI and how LOCI is designed to suppress the noise. We present here several biases that we hare
uncovered while analyzing data on the HR8799 planetary system and how we have modified our analysis pipeline
to calibrate or remove these effects so that high accuracy astrometry and photometry is achievable. In addition,
several new upgrades are presented in a new archive-based (i.e. performing ADI, SSDI and RSDI with LOCI as
a single PSF subtraction step) multi-instrument reduction and analysis pipeline called SOSIE.
Exoplanet Instruments
The Gemini NICI Planet-Finding Campaign
Show abstract
Our team is carrying out a multi-year observing program to directly image and characterize young extrasolar
planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI
is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a
high-performance curvature adaptive optics (AO) system with a simultaneous dual-channel coronagraphic imager.
Combined with state-of-the-art AO observing methods and data processing, NICI typically achieves ≈2
magnitudes better contrast compared to previous ground-based or
space-based planet-finding efforts, at separations
inside of ≈2". In preparation for the Campaign, we carried out efforts to identify previously unrecognized
young stars as targets, to develop a rigorous quantitative method for constructing our observing strategy, and to
optimize the combination of angular differential imaging and spectral differential imaging. The Planet-Finding
Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of
300 stars. We describe the Campaign's goals, design, target selection, implementation, on-sky performance, and
preliminary results. The NICI Planet-Finding Campaign represents the largest and most sensitive imaging survey
to date for massive
(>~ 1 MJup) planets around other stars. Upon completion, the Campaign will establish the best
measurements to date on the properties of young gas-giant planets at
-> 5-10 AU separations. Finally, Campaign
discoveries will be well-suited to long-term orbital monitoring and detailed spectrophotometric followup with
next-generation planet-finding instruments.
Extreme adaptive optics coronagraphy with the high-order test bench in the context of the SPHERE instrument
Show abstract
Extreme adaptive optics systems (XAO) dedicated to the search for extrasolar planets are currently being developed for
8-10 meter telescopes. The High-Order Test bench (HOT) is a
high-contrast imaging adaptive optics bench developed at
the European Southern Observatory to test and optimize different techniques and technologies (e.g. wavefront sensors,
coronagraphs, speckle calibration methods, image post-processing). It reproduces realistic conditions at a telescope (e.g.
Very Large Telescope, VLT), including a turbulence generator, a
high-order adaptive optics system, a near-IR
coronagraph, and sequential differential imaging modes (spectral and polarimetric). We discuss the results of XAO
coronagraphy obtained in the laboratory in the context of imminent planet-finder instruments (e.g. SPHERE1, GPI2, and
HiCIAO3). In particular, results obtained with HOT will be discussed and compared with contrast goals of the near-IR
camera of SPHERE.
System study of EPICS: the exoplanets imager for the E-ELT
Show abstract
ESO and a large European consortium completed the phase-A study of EPICS, an instrument dedicated to exoplanets
direct imaging for the EELT. The very ambitious science goals of EPICS, the imaging of reflected light of mature gas
giant exoplanets around bright stars, sets extremely strong requirements in terms of instrumental contrast achievable. The
segmented nature of an ELT appears as a very large source of quasi-static high order speckles that can impair the
detection of faint sources with small brightness contrast with respect to their parent star. The paper shows how the
overall system has been designed in order to maximize the efficiency of quasi-static speckles rejection by calibration and
post-processing using the spectral and polarization dependency of light waves. The trade-offs that led to the choice of the
concepts for common path and diffraction suppression system is presented. The performance of the instrument is
predicted using simulations of the extreme Adaptive Optics system and polychromatic wave-front propagation through
the various optical elements.
New AO System Designs III
Performance of MEMS-based visible-light adaptive optics at Lick Observatory: closed- and open-loop control
Show abstract
At the University of California's Lick Observatory, we have implemented an on-sky testbed for next-generation
adaptive optics (AO) technologies. The Visible-Light Laser Guidestar Experiments instrument (ViLLaGEs)
includes visible-light AO, a micro-electro-mechanical-systems (MEMS) deformable mirror, and open-loop control
of said MEMS on the 1-meter Nickel telescope at Mt. Hamilton. (Open-loop in this sense refers to the MEMS
being separated optically from the wavefront sensing path; the MEMS is still included in the control loop.) Future
upgrades include predictive control with wind estimation and pyramid wavefront sensing. Our unique optical
layout allows the wavefronts along the open- and closed-loop paths to be measured simultaneously, facilitating
comparison between the two control methods. In this paper we evaluate the performance of ViLLaGEs in openand
closed-loop control, finding that both control methods give equivalent Strehl ratios of up to ~ 7% in I-band
and similar rejection of temporal power. Therefore, we find that open-loop control of MEMS on-sky is as effective
as closed-loop control. Furthermore, after operating the system for three years, we find MEMS technology to
function well in the observatory environment. We construct an error budget for the system, accounting for 130
nm of wavefront error out of 190 nm error in the science-camera PSFs. We find that the dominant known term
is internal static error, and that the known contributions to the error budget from open-loop control (MEMS
model, position repeatability, hysteresis, and WFS linearity) are negligible.
GRAAL: a seeing enhancer for the NIR wide-field imager Hawk-I
Show abstract
We describe the design and development status of GRAAL, the
Ground-layer adaptive optics assisted by Laser, which
will deliver enhanced images to the Hawk-I instrument on the VLT. GRAAL is an adaptive optics module, part of AOF,
the Adaptive optics facility, using four Laser- and one natural
guide-stars to measure the turbulence, and correcting for it
by deforming the adaptive secondary mirror of a Unit telescope in the Paranal observatory.
The outstanding feature of GRAAL is the extremely wide field of view correction, over 10 arcmin diameter, with an
image enhancement of about 20% in average in K band. When observing GRAAL will provide FWHM better than 0.3"
40% of the time. Besides the Adaptive optics facility deformable mirror and Laser guide stars, the system uses subelectron
L3-CCD and a real-time computing platform, SPARTA.
GRAAL completed early this year a final design phase shared internally and outsourced for its mechanical part by the
Spanish company NTE. It is now in manufacturing, with a first light in the laboratory planned in 2011.
Status of the PALM-3000 high-order adaptive optics system
Show abstract
The PALM-3000 upgrade to the Palomar Adaptive Optics system will deliver extreme adaptive optics correction to a
suite of three infrared and visible instruments on the 5.1 meter Hale telescope. PALM-3000 uses a 3388-actuator
tweeter and a 241-actuator woofer deformable mirror, a wavefront sensor with selectable pupil sampling, and an
innovative wavefront control computer based on a cluster of 17 graphics processing units to correct wavefront
aberrations at scales as fine as 8.1 cm at the telescope pupil using natural guide stars. Many components of the system,
including the science instruments and a post-coronagraphic calibration wavefront sensor, have already been
commissioned on the sky. Results from a laboratory testbed used to characterize the remaining new components and
verify all interfaces are reported. Deployment to Palomar Observatory is planned August 2010, with first light expected
in early 2011.
ALTAIR performance and updates at Gemini North
Show abstract
We present up-to-date performance characteristics for natural guide star (NGS) operation of the ALTAIR adaptive optics
system at the Gemini N. 8m telescope. These results are obtained from a nightly performance monitoring campaign
where we obtain a consistent set of point spread functions (PSFs) over a broad range of observing conditions. These
results are compared with system modelling and circular buffer information from the Altair adaptive optics (AO) system.
The latter show residual tip-tilt errors with a median rms ~ 18.5 mas. We also present preliminary results from a new
operational mode of the laser guide star (LGS) AO which will eventually yield all-sky access with image FWHM ~ 0.1"
- 0.2".
The MCAO systems within LINC-NIRVANA: control aspects in addition to wavefront correction
Show abstract
LINC-NIRVANA is the near-infrared homothetic imaging camera for the Large Binocular Telescope. Once
operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view. Its
layer-oriented MCAO systems (one for each arm of the interferometer) are conjugated to the ground layer and
an additional layer in the upper atmosphere. In this contribution MCAO wavefront control is discussed in the
context of the overall control scheme for LINC-NIRVANA. Special attention is paid to a set of auxiliary control
tasks which are mandatory for MCAO operation: The Fields of View of each wavefront sensor in the instrument
have to be derotated independent from each other and independently from the science field. Any wavefront
information obtained by the sensors has to be matched to the time invariant modes of the deformable mirrors
in the system. The tip/tilt control scheme is outlined, in which atmospheric, but also instrumental tip/tilt
corrections are sensed with the high layer wavefront sensor and corrected by the adaptive secondary mirror of
the LBT. Slow image motion effects on the science detector have to be considered, which are caused by flexure
in the non-common path between AO and the science camera, atmospheric differential refraction, and alignment
tolerances of the derotators. Last but not least: The sensor optics (pyramids) have to be accurately positioned
at the images of natural reference stars.
Laser Systems
PM fiber lasers at 589nm: a 20W transportable laser system for LGS return flux studies
Show abstract
In this paper we present the rationale and design of a compact, transportable, modular Laser Guide Star Unit, comprising
a 589nm laser mounted on a 300mm launch telescope, to be used in future experiments probing the mesospheric sodium
properties and to validate existing LGS return flux simulations. The 20W CW 589nm Laser is based on the ESO
developed concept of 589nm lasers based on Raman Fiber Amplifiers, refined and assembled together with industry. It
has the same laser architecture as the laser which will be used for the VLT Adaptive Optics Facility. We have added to
the 20W CW laser system the capabilities of changing output polarization, D2b emission levels, power level, linewidth
and to operate as pulsed laser with amplitude modulation. We focus in this paper on the laser description and test results.
Keck I laser guide star AO system integration
Show abstract
With the much anticipated delivery of the Lockheed Martin Coherent Technology Quasi-CW laser, the W. M. Keck
Observatory was able to complete the installation and integration of the Laser Guide Star Adaptive Optics System on the
Keck I telescope. The Keck I LGSAO system was developed to provide redundancy for the Keck II system as well as
balancing the instrumentation load between the two telescopes and interferometers. With the improved sodium coupling
efficiency of the laser and a center launching system, the Keck I laser performance is expected to exceed those on the
Keck II system.
We present the challenges of integrating the Keck I Laser Guide Star Adaptive Optics System on an operational
telescope. We will present issues and performance data related to the primary subsystem components such as the laser
itself, the Selex Galileo Avionica launch telescope, the Mitsubishi fiber transport, and the Adaptive Optics System. The
paper will also focus on the integration and testing performed at the W. M. Keck headquarters as well as the summit of
Mauna Kea. We will present initial first light performance of the Keck I LGSAO System and compare those to the
existing Keck II LGSAO System.
Setting up ELP-OA: the polychromatic laser guide star demonstrator
Show abstract
ELP-OA ('Etoile Laser Polychromatique pour l'Optique Adaptative) aims at demonstrating the tip-tilt is measurable
with a Laser Guide Star (LGS) without any natural guide star. This allows a full sky coverage down to
visible wavelengths. ELP-OA is being setup at Observatoire de
Haute-Provence (OHP). To create a polychromatic
LGS, we use two pulsed dye lasers (at 569nm and 589nm) to produce a two-photons excitation of sodium
atoms in the mesosphere. The chromatism of the refractive index of the air yields a difference of the LGS
direction at different wavelengths. The position differences is proportionnal to the tip-tilt. Since the LGS isn't
sharp enough to give us a small enough error in the differential
tip-tilt, we use an interferometric projector to
improve the high spatial information in the laser spot. It requires an adaptive optics working down to 330nm.
This one is done by post-processing algorithms. Two two aperture projectors are used. Each one creates a
fringe-modulated LGS, and a better RMS error in the LGS position is obtained by measuring the information
in a normal direction with respect to the fringes. By using a two aperture projector, we also strongly decrease
the negative effect of the laser star elongation in the mesosphere, and the Rayleigh contribution near the LGS.
We propose a new optimal algorithm to retrieve the tip-tilt from simultaneous images at different wavelengths.
To enhance the RMS error of the measurements, we extend this algorithm to exploit the temporal correlation
of the turbulence.
A bright, pulsed, guide star laser for very large telescopes
Show abstract
We demonstrate for the first time the practical feasibility of a new sodium guide star laser with a
pulsed burst output of sufficient energy at 589nm to be useful for current applications and readily
scalable to meet future requirements. We describe complete experimental design verification results
of the pulse burst laser concept, optimized to eliminate guide-star elongation issues and to meet all
requirements for Multi Conjugate Adaptive Optics (MCAO) for future extremely large ground-based
telescopes (ELTs). It makes use of sum frequency generation (SFG) of two, Q-switched, injection
mode-locked, wavelength stabilized Nd:YAG lasers, producing a
macro-micro, pulse-burst output
which is optimized in power and bandwidth to maximize the fluorescence from the high altitude
sodium layer.
System overview of 30 W and 55 W sodium guide star laser systems
Show abstract
We report on the successful delivery of a 30 W solid-state sodium Guide Star Laser System (GLS) to the W. M. Keck
Observatory in 2009, and the demonstration of a 55 W GLS delivered to the Gemini South Observatory in 2010. This
paper describes the GLS performance results of both the Keck I and Gemini South GLSs with an emphasis on the system
design and delivered performance. The 589 nm output was generated via Sum Frequency Mixing (SFM) of 1064 nm
and 1319 nm Nd:YAG lasers in a LBO (Lithium Triborate) nonlinear crystal. The Keck GLS underwent extensive
testing and has demonstrated consistent performance with a CW mode-locked output of > 30 W and measured beam
quality of M2 < 1.2 while locked to the sodium D2a transition. The Keck GLS was installed on the telescope in late 2009
and first light on the sky was achieved in early 2010. Factory testing of the Gemini South GLS shows a CW modelocked
output of > 55 W and measured M2 ~1.2 while locked to the sodium D2a line center. The Gemini South GLS has
produced a maximum power of 76 W at 589 nm with 85 W of 1319 nm and 110 W of 1064 nm as inputs to the SFM,
representing a single-pass conversion efficiency of 39%.
Atmospheric Characterization
Open questions in site characterization and turbulence parameter measurements
Show abstract
With the development of increasingly larger and more complex telescopes and instrumentation, site testing and
characterization efforts also increase in both magnitude and complexity. This happens because the investment
into larger observatories is higher and because new technologies, such as adaptive optics, require knowledge about
parameters that did not matter previously, such as the vertical distribution of turbulence. We present examples
of remaining questions which, to date, are not generally addressed by "standard" site characterization efforts,
either because they are technically not (yet) feasible or because they are impractical. We center our observations
around the experience gained during the Thirty Meter Telescope (TMT) site testing effort with an emphasis
on turbulence measurements, but our findings are applicable in general to other current and future projects as
well.
High-resolution mesospheric sodium observations for extremely large telescopes
Show abstract
Variations in density structure and altitude of mesospheric sodium impact the performance of adaptive optics
systems employing sodium laser guide stars. The associated wave-front errors grow as the square of the telescope
aperture and will be very significant for the next generation of large-aperture ground-based optical/infrared
telescopes. To support the adaptive optics program for the Thirty Meter Telescope and European Extremely
Large Telescope, we are conducting a program of sodium monitoring using a high-resolution sodium lidar system
on the 6-meter Large Zenith Telescope (LZT). Located at 49°N latitude, the LZT lidar system provides density
profiles with spatial and temporal resolution sampling of 4.8 m and 20 ms. In this paper we report highlights of
results obtained over two years of observations.
Diode-seeded fiber-based sodium laser guide stars ready for deployment
Show abstract
The quest of the astronomical instrumentation community for
high-power, narrow-band CW laser guide stars (LGS)
has been a challenge to the laser community for more than two decades now. Only recently, a new generation of
rugged laser system developments has started to provide the laser infrastructure for the next generation earth-bound
telescopes. We report on the system design of four 20W CW
diode-seeded fiber-amplified laser guide star for
deployment at the VLT in 2013.
Innovative AO Concepts
Recent progress and perspectives for GLAO and MOAO
Show abstract
Ground Layer Adaptive Optics (GLAO) is a relatively novel form of AO designed to provide image improvements over
fields of view of ~10' or greater. A representative range of GLAO instrumentation projects from 4m to 42m are
summarised. A related form of wide field AO is Multi-Object Adaptive Optics (MOAO). Here, much higher correction is
required, but only for sparsely distributed "islands". The correction is applied in open-loop, and this feature, plus the high
accuracy, wide field tomography required, mean that MOAO involves considerable technological development. Several
pathfinders, as well as actual MOAO facility projects, are underway, and are surveyed here.
Adaptive optics with solely natural guide stars for an extremely large telescope
Show abstract
In the past decade the ingredients for making real an Extremely Large Telescope with an Adaptive Optics system driven
solely by Natural Guide Stars have been conceived, developed, built and proven on the sky. Still, the straightforward
merging of these concepts is not enough to fulfill such an ambitious goal. We show here that a combination of the layeroriented
approach, the virtual deformable mirrors concept, and a combined use of different kind of wavefront sensors,
some taking advantage of working in Closed Loop and some other characterized by an extremely high dynamic range,
make the goal a reachable one. It is remarkable that such an approach requires, on a telescope of ELT class, including a
common Deformable Mirror conjugated to the entrance pupil or close-by, a minimum impact on the guide probe units.
The last involves the adoption of small Closed Loop AO system with an extremely high dynamic range wavefront sensor
looking at the detailed shape of a small Deformable Mirror that allows the use of sensors taking advantage of the Closed
Loop conditions. A pyramid wavefront sensor, fed by the Natural Guide Stars light and closing the loop with the mirror,
and a YAW wavefront sensor looking at the mirror itself, allow for a natural and efficient combination of the data. The
limits in the Field of View covered by such an approach are given by pure meta-pupils superimposition rather than to the
spatial frequency of the achievable correction, breaking the limits previously thought for this kind of systems. The
overall combination leads to a significant sky coverage, with performances comparable to the ones under discussion for
some Laser Guide Stars approaches, without the related hurdle. The small technical impact on the telescope makes this
approach not directly in-conflict with a Laser Guide Stars one allowing the designer to keep all the options on the table
up to a very late stage.
The Subaru coronagraphic extreme AO (SCExAO) system: wavefront control and detection of exoplanets with coherent light modulation in the focal plane
Show abstract
The Subaru Coronagraphic Extreme-AO (SCExAO) system is designed for high contrast coronagraphic imaging at small angular separations, and is scheduled to see first light on the Subaru Telescope in early 2011. The wavefront control architecture for SCExAO is optimized for scattered light control and calibration at small angular separations, and is described in this paper. Key subsystems for the SCExAO wavefront control architecture have been successfully demonstrated, and we report results from these tests and discuss their role in the SCExAO system. Among these subsystems, a technique which can calibrate and remove static and slow speckles which traditionally limit high contrast detections is discussed. A visible light lab prototype system at Subaru Telescope recently demonstrated speckle halo reduction to 2e-7 contrast within 2 2λ/D, and removal of static coherent speckles to 3e-9 contrast.
Optimal LGS pointing with faint tip-tilt NGS
Show abstract
Experience with the current generation of astronomical single laser guide star (LGS) adaptive optics (AO) systems
has demonstrated system performance that is often limited by residual tip-tilt errors induced by the paucity of
bright tip-tilt natural guide stars (NGS). To overcome this limitation, we are developing a new generation of
tip-tilt sensors that will operate at near-infrared wavelengths where the NGS is sharpened to the diffraction limit.
To optimize performance, single LGS AO systems utilizing sharpened tip-tilt NGS should generally not point
their LGS directly toward their science target. Rather, optimal performance for wide sky coverage is obtained by
offsetting LGS pointing along a radius connecting the science target and the tip-tilt NGS. We demonstrate that
determination of the jointly optimized LGS pointing angle and tip-tilt wavefront sensor (WFS) integration time
can improve performance metrics by factors of several, particularly for faintest NGS operation. We find the LGS
offset should be as much as 1/2 the distance to the NGS to maximize Strehl ratio at near-infrared wavelengths
and ≈ 1/4 the distance to the NGS to maximize ensquared energy, with lesser off-pointing for brighter NGS.
Future AO systems may benefit from predictive determination of optimal LGS offsetting, based upon changing
atmospheric conditions and observational geometries.
Experimental demonstration of laser tomographic adaptive optics on a 30-meter telescope at 800 nm
Show abstract
A critical goal in the next decade is to develop techniques that will extend Adaptive Optics correction to visible
wavelengths on Extremely Large Telescopes (ELTs). We demonstrate in the laboratory the highly accurate atmospheric
tomography necessary to defeat the cone effect on ELTs, an essential milestone on the path to this capability. We
simulate a high-order Laser Tomographic AO System for a 30-meter telescope with the LTAO/MOAO testbed at UCSC.
Eight Sodium Laser Guide Stars (LGSs) are sensed by 99x99 Shack-Hartmann wavefront sensors over 75". The AO
system is diffraction-limited at a science wavelength of 800 nm
(S ~ 6-9%) over a field of regard of 20" diameter. Openloop
WFS systematic error is observed to be proportional to the total input atmospheric disturbance and is nearly the
dominant error budget term (81 nm RMS), exceeded only by tomographic wavefront estimation error (92 nm RMS).
The total residual wavefront error for this experiment is comparable to that expected for wide-field tomographic adaptive
optics systems of similar wavefront sensor order and LGS constellation geometry planned for Extremely Large
Telescopes.
Wavefront Sensors II
Compared performance of different centroiding algorithms for high-pass filtered laser guide star Shack-Hartmann wavefront sensors
Show abstract
Variations of the sodium layer altitude and atom density profile induce errors on laser-guide-star (LGS) adaptive
optics systems. These errors must be mitigated by (i), optimizing the LGS wavefront sensor (WFS) and the
centroiding algorithm, and (ii), by adding a high-pass filter on the LGS path and a low-bandwidth
natural-guide-star WFS. In the context of the ESO E-ELT project, five centroiding algorithms, namely the centre-of-gravity
(CoG), the weighted CoG, the matched filter, the quad-cell and the correlation, have been evaluated in closedloop
on the University of Victoria LGS wavefront sensing test bed. Each centroiding algorithm performance is
compared for a central versus side-launch laser, different fields of view, pixel sampling, and LGS flux.
Wavefront sensing with laser guide stars on the ELTs
Show abstract
Adaptive Optics (AO) relies on aWave Front Sensor (WFS) to measure properly the perturbations induced by the
turbulence on the wavefront. Yet, source extension may limit its performance. In the case of a Shack-Hartmann
(SH) WFS associated to one or more Laser Guide Stars (LGS), this extension becomes all the more problematic
as the diameter of the telescope tends to increase. In order to mitigate the effects induced by the spot elongation
on the quality of the WFS measurements, various algorithms are used. Most of them are non-linear, and require
a reference. The design of the SH WFS itself has an influence on the measurement quality, as it also induces
non-linearities. In addition, the time-evolving structure of the LGS, due to the fluctuations of the Sodium layer,
has an impact on the measurements as well. Eventually, both influences are coupled in the wavefront sensing
process. The present study is aimed at optimizing a whole set of carefully chosen parameters defining the design
of a SH WFS, in the particular case of a LGS on an ELT. The relative impact of these parameters are studied
first at the subaperture level, and then on the reconstructed wavefront.
A simple and efficient model for polychromatic focal plane wave-front sensor
Show abstract
Phase Diversity is a focal-plane technique which is chromatic by nature. The use of a monochromatic
model on wide-band imaging results of an additional error function of the spectral range.We present here a
second order modeling of the focal plane wave-front sensing error due to wide-band imaging and propose
a first order correction by inverse problem and the first results of an end-to-end simulation for an iterative
correction. Simulation results of 20 nm wave-front aberrations show that the reconstruction error decreases
from 10 nm with classical focal-plane sensor to sub-nanometric error with optimal correction at Δλ = 500 nm.
Advanced static speckle calibration for exoplanet imaging
Show abstract
In this communication we address the problem of post coronagraphic wavefront reconstruction. In high contrast
imaging applications it is crucial to estimate the wavefront after the coronagraph, as close as possible to the
science camera, in order to minimize non-common path errors. However closing the loop on such a measurement
is a difficult exercise since several low order modes have been cancelled by the coronagraphs, thus leading to
ill-posed inversion problems. Moreover sensing at the science detector is an intrusive method that disrupts the
course of the observations. The Gemini Planet Imager (GPI) calibration system, based on a post-coronagraphic
interferometer, provides an estimate of mid to high spatial frequencies aberrations that alleviates these two issues.
However such a measurement have an intrinsic limitations that is related to the differential path errors between
the two arm of the interferometer. In this paper we show how to devise wavefront reconstruction algorithms that
account for these differential path errors. We identify two regimes, relative and absolute wavefront sensing, that
depend on the magnitudes of the aberrations and the design of the coronagraph. We illustrate the performances
for each regime. Finally we present experimental results obtained during the validation phase of show the results
on laboratory data.
Wavefront Correctors
Contactless thin adaptive mirror technology: past, present, and future
Show abstract
The contactless, voice coil motor adaptive mirror technology starts from an idea by Piero Salinari in 1993. This idea has
progressively evolved to real systems thanks to a fruitful collaboration involving Italian research institutes
(INAF - Osservatorio Astrofisico di Arcetri and Aerospace Department of Politecnico di Milano) and small Italian enterprises
(Microgate and ADS). Collaboration between research institutions and industry is still very effectively in place, but
nowadays the technology has left the initial R&D phase reaching a stage in which the whole projects are managed by the
industrial entities. In this paper we present the baseline concept and its evolution, describing the main progress
milestones. These are paced by the actual implementation of this idea into real systems, from MMT, to LBT, Magellan,
VLT, GMT and E-ELT. The fundamental concept and layout has remained unchanged through this evolution,
maintaining its intrinsic advantages: tolerance to actuators' failures, mechanical de-coupling and relaxed tolerances
between correcting mirror and reference structure, large stroke, hysteresis-free behavior. Moreover, this concept has
proved its expandability to very large systems with thousands of controlled d.o.f. Notwithstanding the solidity of the
fundamentals, the implementation has strongly evolved from the beginning, in order to deal with the dimensional, power,
maintainability and reliability constraints imposed by the increased size of the targeted systems.
The adaptive secondary mirror for the Large Binocular Telescope: optical acceptance test and preliminary on-sky commissioning results
Show abstract
The Large Binocular Telescope (LBT) has two adaptive secondary mirrors based on 672 voice-coil force actuators. The
shape of the mirror is controlled using internal metrology based on co-located capacitive sensors. The first mirror unit is
currently mounted on LBT for on-sky commissioning as part of the First Light Adaptive Optics System (FLAO). During
spring-time 2009 the optical acceptance test was performed using the 14-m optical test tower at the Osservatorio
Astrofisico di Arcetri (INAF) showing the capability of flattening the shell at the level of 14nm rms residual surface
error. This paper reports the optical layout, calibration procedures and results of the optical acceptance test. Moreover we
report the first results obtained during the early runs of FLAO commissioning showing the ability of the mirror to
compensate for atmospheric turbulence with extremely high Strehl ratio values (better than 80% in H-band) as permitted
by the largest number of correcting degrees of freedom currently available on-sky for astronomical telescopes.
MEMS deformable mirrors for astronomical adaptive optics
Show abstract
We report on the development of high actuator count,
micro-electromechanical (MEMS) deformable mirrors designed
for high order wavefront correction in ground and space-based astronomical adaptive optics instruments. The design of
these polysilicon, surface-micromachined MEMS deformable mirrors builds on technology that has been used
extensively to correct for ocular aberrations in retinal imaging systems and for compensation of atmospheric turbulence
in free-space laser communication. These light-weight, low power deformable mirrors have an active aperture of up to
25.2mm consisting of a thin silicon membrane mirror supported by an array of 140 to 4092 electrostatic actuators which
exhibit no hysteresis and have sub-nanometer repeatability making them well suited for open-loop control applications
such as Multi-Object Adaptive Optics (MOAO). The continuous membrane deformable mirrors, coated with a highly
reflective metal film, are capable of up to 6μm of stroke, have a surface finish of <10nm RMS with a fill factor of 99.8%.
Presented in this paper are device characteristics and performance test results, as well as reliability test data and device
lifetime predictions that show that trillions of actuator cycles can be achieved without failures.
Optical characterization of the PALM-3000 3388-actuator deformable mirror
Show abstract
We describe the lab characterization of the new 3,388-actuator deformable mirror (DM3388) produced by Xinetics, Inc.
for the PALM-3000 adaptive optics (AO) system1 under development by Jet Propulsion Laboratory and Caltech Optical
Observatories. This square grid 66-by-66 actuator mirror has the largest number of actuators of any deformable mirror
currently available and will enable high-contrast imaging for direct exoplanet imaging science at the Palomar 200"
diameter Hale Telescope. We present optical measurements of the powered and unpowered mirror surface, influence
functions, linearity of the actuators, and creep of the actuators. We also quantify the effect of changes in humidity.
Last progress concerning the design of the piezo-stack M4 adaptive unit of the E-ELT
Show abstract
CILAS proposes a M4 adaptive mirror (M4AM) that corrects the atmospheric turbulence at high frequencies and residual
tip-tilt and defocus due to telescope vibrations by using piezostack actuators. The design presents a matrix of 7217
actuators (triangular geometry, spacing equal to 29 mm) leading to a fitting error reaching the goal. The mirror is held by
a positioning system which ensures all movements of the mirror at low frequency and selects the focus (Nasmyth A or B)
using a hexapod concept. This subsystem is fixed rigidly to the mounting system and permits mirror displacements. The
M4 control system (M4CS) ensures the connection between the telescope control/monitoring system and the M4 unit - positioning system (M4PS) and piezostack actuators of the M4AM in particular. This subsystem is composed of
electronic boards, mechanical support fixed to the mounting structure and the thermal hardware. With piezostack
actuators, most of the thermal load is minimized and dissipated in the electronic boards and not in the adaptive mirror.
The mounting structure (M4MS) is the mechanical interface with the telescope (and the ARU in particular) and ensures
the integrity and stability of M4 unit subsystems. M4 positioning system and mounting structure are subcontracted to
AMOS company.
Real-Time Control II
MYST: a comprehensive high-level AO control tool for GeMS
Show abstract
Myst is the Gemini MCAO System (GeMS) high level control GUI. It is written in yorick, python and C. In this
paper, we review the software architecture of Myst and its primary purposes, which are many: Real-time display,
high level diagnostics, calibrations, and executor/sequencer of high level actions (closing the loop, coordinating
dithers, etc).
SPARTA for the VLT: status and plans
Show abstract
SPARTATM, the ESO Standard Platform for Adaptive optics Real Time Applications, is the real time computing
platform serving 3 major 2nd generation instruments at the VLT (SPHERE, GALACSI and GRAAL) with plans to serve
more, smaller, instruments in the near future. SPARTA offers a very modular and fine-grained architecture which is
generic enough to serve a variety of AO systems. SPARTA includes the definitions of all the interfaces between those
modules and provides libraries and tools to implement and test the various modules as well as a map to technologies
capable of delivering the required performance, most of them innovative with respect to ESO standards in use.
For the above mentioned instruments, SPARTA provides also a complete implementation of the AO application, with
features customized for each of the 3 instruments. In this paper we present the architecture of SPARTA, its technologies,
functions, performance and test tools as well as the plans to increase the reach of the platform to smaller system with
what we call SPARTA Light.
Wavefront sensing and wavefront reconstruction for the 4m European Solar Telescope EST
Show abstract
We give an overview of the Adaptive Optics (AO) and Multi-conjugate Adaptive Optics (MCAO) system of the
planned 4m European Solar Telescope (EST). The parameter space and the problems of solar MCAO working
in the visible are explained. The wavefront reconstruction schemes presently being considered are explained.
First estimates of the expected MCAO performance for varying parameter sets are given.
Poster Sessions
Maintenance and operation of the adaptive optics module for NICI, the high-contrast coronagraphic imager of GEMINI observatory
Show abstract
NICI, the high-contrast coronagraphic imager of Gemini observatory, primarily dedicated to planet hunting has
been offered to the astronomical community since end of 2008. We present our experiences in operating and
maintaining NICI's 85 element curvature adaptive optics (AO) system. A detailed study of NICI AO telemetry
data is also most relevant to prepare the arrival of next generation instruments. We summarize the behavior
of interaction matrices, control matrices and error transfer functions under different operational conditions; a
detailed understanding of the system helps monitoring and optimizing performance. Furthermore, we describe
tuning (membrane mirror stroke/extra focal distance) for non-optimal seeing conditions as well as for niche
applications of NICI such as observing small moons and asteroids. We compare on-sky measurements to theory
or simulations.
MOAO activities in Tohoku University
Show abstract
We started adaptive optics (AO) development activities in Tohoku university targeting Multi-Object Adaptive
Optics (MOAO) system for the next generation ground-based large telescopes. In order to realize an MOAO
system, we are currently conducting two R&Ds. First one is a development of a large stroke (20μm) Micro Electro
Mechanical Systems (MEMS) deformable mirror with large number of elements (>3000) which is necessary to
achieve mild Strehl Ratio in an AO systems for 30m class telescopes. Based on our original design to achieve
the requirements, prototyping of the device is currently underway using the MEMS development facility in our
university. Second one is a consideration of tomographic algorithm for the wavefront estimation required for
an MOAO system. The algorithm will be tested on a test bench simulating multiple guide stars and wavefront
sensors. Concept design of the test bench is shown. MEMS-DM and MOAO testbed developments will be
concluded by 2013.
A compact design of a WFS for a natural guide star-based ELT adaptive optics system
Show abstract
We describe the opto-mechanical implementation of a group of wavefront sensors able to drive an MCAO system in
order to cover a Field of View of the order of 1-2 arc-minutes, but getting advantages from the starlight coming from a
Field of View as large as 10 arc-minutes in diameter. This involves a number of arms with a miniaturized, very small
Field of View, single reference Adaptive Optics systems. A pyramid wavefront sensor working in close loop is fed
through a small Deformable Mirror that is continuously monitored by an extremely high dynamic range wavefront
sensor, whose signal has similar modality than the Pyramid one, namely YAW.
In this way, a very compact wavefront sensor with a dynamic range limited by the stroke of the Deformable Mirror is
achieved. Such a sensor is characterized by a limiting magnitude performances typical of a closed loop coherent
wavefront sensor. This concept, in addition with an architecture of a Wavefront Computer that allows the
implementation of a number of virtual Deformable Mirrors, allows for the development of a NGS based concept
described elsewhere. Emphasis is given in this talk to the practical implementation and to the opto-mechanical details,
including an overview of the required components, especially the detectors and the deformable mirrors and we show that
the goal is attainable with today existing components.
Status and new operation modes of the versatile VLT/NaCo
Show abstract
This paper aims at giving an update on the most versatile Adaptive Optics fed instrument to date, the well
known and successful NACO*. Although NACO is only scheduled for about two more years† at the Very Large
Telescope (VLT), it keeps on evolving with additional operation modes bringing original astronomical results.
The high contrast imaging community uses it creatively as a test-bench for SPHERE‡ and other second generation
planet imagers. A new visible wavefront sensor (WFS) optimized for Laser Guide Star (LGS) operations has
been installed and tested, the cube mode is more and more required for frame selection on bright sources, a
seeing enhancer mode (no tip/tilt correction) is now offered to provide full sky coverage and welcome all kind
of extragalactic applications, etc. The Instrument Operations Team (IOT) and Paranal engineers are currently
working hard at maintaining the instrument overall performances but also at improving them and offering new
capabilities, providing the community with a well tuned and original instrument for the remaining time it is
being used. The present contribution delivers a non-exhaustive overview of the new modes and experiments that
have been carried out in the past months.
Fast autonomous holographic adaptive optics
Show abstract
We have created a new adaptive optics system using a holographic modal wavefront sensing method capable of
autonomous (computer-free) closed-loop control of a MEMS deformable mirror. A multiplexed hologram is recorded
using the maximum and minimum actuator positions on the deformable mirror as the "modes". On reconstruction, an
input beam will be diffracted into pairs of focal spots - the ratio of particular pairs determines the absolute wavefront
phase at a particular actuator location. The wavefront measurement is made using a fast, sensitive photo-detector array
such as a multi-pixel photon counters. This information is then used to directly control each actuator in the MEMS DM
without the need for any computer in the loop.
We present initial results of a 32-actuator prototype device. We further demonstrate that being an all-optical, parallel
processing scheme, the speed is independent of the number of actuators. In fact, the limitations on speed are ultimately
determined by the maximum driving speed of the DM actuators themselves. Finally, being modal in nature, the system is
largely insensitive to both obscuration and scintillation. This should make it ideal for laser beam transmission or imaging
under highly turbulent conditions.
Residual tip-tilt motion of LGS in monostatic scheme
Show abstract
There is analyzed the possibility the general tilt correction of the wave front on base of the laser guide star (LGS) signal.
The calculation of the image motion of the spherical wave (that position the source of radiation also fluctuated) with
random center is conducted. The exact formula for random vector defining the position of the image of the spherical
wave in focal plane of the telescope is offered.
The variance of residual fluctuations has been calculated. The variance behavior of this residual motion from optical
experiment parameters are analyses. The similar problem under solution of the some practical tasks, including the
possibility of the wave front "global" tilt correction with using single LGS, can be appeared.
Online wind estimation and prediction for a two-layer frozen flow atmosphere
Show abstract
We present a method for online estimation and prediction of wavefront distortions caused by two independent
layers of frozen flow turbulence. The key to this algorithm is a fast, gradient-based estimator that uses optical
flow techniques to extract the bulk velocity vectors of the two wind layers from three consecutive measurements
of their combined wavefront. Once these velocity vectors are known, the phase aberrations resulting from the
two-layer atmosphere can be predicted at any future time using a linear combination of shifted wavefronts. This
allows calculation of a deformable mirror correction that compensates for the time delay errors in the control
loop. Predictive control will be especially beneficial for visible light and high-contrast astronomical adaptive
optics as well as for any adaptive optics system whose performance suffers due to time delay errors. A multilayer
approach to predictive control is necessary since most observing sites have multi-layer atmospheres. The
spatial domain method that we present is attractive because it uses all spatial frequency components of the
wavefront simultaneously to find a global wind model. Its ability to update the wind velocity estimate at each
control cycle makes it sensitive to changes in the wind on the order of tens of milliseconds. Our simulations
show a potential Strehl increase from 0.45 to 0.65 for visible-light adaptive optics in low-noise, moderate-wind
conditions with two frozen-flow wind layers and a strong static layer.
Laboratory demonstration of an anti-halo reconstructor for closed-loop adaptive halo suppression
Show abstract
In order to suppress the halo and any residual speckles over a region of interest, we find an anti-halo reconstructor which
gives the required changes to a deformable mirror (DM) at the pupil plane. The reconstructor is built from a training set
consisting of measurements of the complex halo influence functions for a spanning set of Fourier modes applied to the
DM. The reconstructor is then found by multiplying the applied DM actuator values by the singular value decomposition
(SVD) pseudo-inverse of the measured complex halo influence functions. Using a single fully illuminated 12×12
actuator DM at the pupil plane, halo suppression for complex pupils out to the control radius of 6 λ/D can be provided.
In practice, a coronagraph is unlikely to achieve high performance without adaptive tuning. We use a coronagraphic
focal plane interferometer [1], where the focal plane mask diverts the bright starlight for use as an interferometric
reference beam to measure the residual complex halo. The result of the reconstructor acting on the complex halo
measurements allowed us to implement a closed loop halo-suppression servo. We discuss the laboratory implementation
and experience with this technique.
Reducing PSF halo with adaptive pupil masking
Show abstract
Adaptive pupil masking can be used to reduce the halo and increase the peak intensity of a point spread
function (PSF) using an adaptive pupil mask. Areas of the pupil where the residual wavefront aberrations
are large are selected and masked using a spatial light modulator. The technique can be used as a standalone
system on a smaller telescope without adaptive optics or in conjunction with an adaptive optics system to
further improve the PSF. We find by simulation that for a 1 m telescope and using an 8 × 8 system we can
increase the peak intensity by 40 % and reduce the FWHM by 76 % to near the diffraction limit. For an 8 m
class telescope with a 16×16 pupil mask and adaptive optics the intensity was found to increase by 23 % and
the FWHM reduced from 0.022" to 0.018". We also examine the effects of the adaptive pupil mask on the
diffraction limited PSF. The square blocking elements result in a square diffraction pattern superimposed
on the standard circular diffraction pattern. The relative strengths of each depend on the fraction of the
pupil which is blocked.
Ferrofluid deformable mirrors: recent advances and results
Show abstract
Many technical improvements have been made since we first introduced deformable mirrors that use magnetic liquids
(ferrofluids) whose surface are shaped by arrays of small electric coils. We present recent advances and experimental
results of a 91-actuator magnetic liquid deformable mirror that uses a novel technique that linearizes their response by
placing the array of actuators inside a strong and uniform magnetic field. We show that this improved ferrofluid
deformable mirror (FDM) can produce inter-actuator strokes of over 10 μm, is capable of generating wavefront having
peak-to-valley amplitudes of over 60 μm, and predict that amplitudes greater than 100 μm are achievable. We also
present experimental results showing that these improved FDMs are good candidates for astronomical, vision science,
and optical testing applications.
The Magellan Adaptive Secondary VisAO Camera: diffraction-limited broadband visible imaging and 20mas fiber array IFU
Show abstract
The Magellan Adaptive Secondary AO system, scheduled for first light in the fall of 2011, will be able to simultaneously
perform diffraction limited AO science in both the mid-IR, using the BLINC/MIRAC4 10μm camera, and in the visible
using our novel VisAO camera. The VisAO camera will be able to operate as either an imager, using a CCD47 with 8.5
mas pixels, or as an IFS, using a custom fiber array at the focal plane with 20 mas elements in its highest resolution
mode. In imaging mode, the VisAO camera will have a full suite of filters, coronagraphic focal plane occulting spots,
and SDI prism/filters. The imaging mode should provide ~20% mean Strehl diffraction-limited images over the band
0.5-1.0 μm. In IFS mode, the VisAO instrument will provide R~1,800 spectra over the band 0.6-1.05 μm. Our
unprecedented 20 mas spatially resolved visible spectra would be the highest spatial resolution achieved to date, either
from the ground or in space. We also present lab results from our recently fabricated advanced triplet Atmospheric
Dispersion Corrector (ADC) and the design of our novel wide-field acquisition and active optics lens. The advanced
ADC is designed to perform 58% better than conventional doublet ADCs and is one of the enabling technologies that
will allow us to achieve broadband (0.5-1.0μm) diffraction limited imaging and wavefront sensing in the visible.
Diffraction limited operation with ARGOS: a hybrid AO system
Show abstract
ARGOS, the Laser Guide Star (LGS) facility of the Large Binocular Telescope (LBT), implements a Ground
Layer Adaptive Optics (GLAO) system, using 3 low-altitude beacons, to improve the resolution over the 4'×4'
FoV of the imager and Multi Object Spectrograph (MOS) LUCIFER. In this paper we discuss the performance
and the reconstruction scheme of an hybrid AO system using the ARGOS Rayleigh beacons complemented with a
single faint high-altitude star (NGS or sodium beacon) to sense the turbulence of the upper atmosphere allowing
an high degree of on-axis correction.
With the ARGOS system, the NGS-upgrade can be immediately implemented at LBT using the already existing
Pyramid WFS offering performance similar to the NGS AO system with the advantage of a larger sky coverage.
New method of fabricating phase screens for simulated atmospheric turbulence
Show abstract
The ability to simulate atmospheric turbulence is a crucial part of enabling adaptive optics
technology to function and evolve. We report a new technique of creating phase plates
developed at the Laboratory for Adaptive Optics (LAO) which involves the application of clear
acrylic paint onto a transparent substrate. Results of interferometric characterization of these
plates is described and compared to Kolmolgorov statistics. These plates have been successfully
used in the Multi-Conjugate Adaptive Optics (MCAO) testbed and as part of the Villages
(Visible Light Laser Guidestar Experiments) calibration system.
System overview of the Multi conjugated Adaptive Optics RelaY for the E-ELT
Show abstract
MAORY, the Multi-conjugated Adaptive Optics RelaY for the European Extremely Large Telescope, will be located on
one of the Nasmyth platforms of the telescope to provide multi conjugated adaptive optics correction of the wavefront.
The scientific instruments fed by the module will benefit from a corrected field of view of 2 arcmin diameter with high
performance uniformity across the field. The two post-focal deformable mirrors are projected at high altitude by the
optical system based on 5 mirrors and one dichroic which splits the laser light of the artificial reference stars from the
science channel. The third deformable mirror, conjugated to the ground, is integrated into the telescope. Six laser guide
stars are foreseen in order to measure the wavefront distortions and three natural guide stars are used to solve the tip-tilt
indetermination problem. The natural guide stars wavefront sensors are located close to the output focal plane in order to
minimize the non common path aberrations. Two output ports are foreseen: one gravity invariant located below the
optical bench and one on one side of the bench to feed large instruments placed on the Nasmyth platform.
Calibration strategy and optics for ARGOS at the LBT
Show abstract
Effective calibration procedures play an important role for the efficiency and performance of astronomical
instrumentation. We report on the calibration scheme for ARGOS, the Laser Guide Star (LGS) facility at the LBT. An
artificial light source is used to feign the real laser beacons and perform extensive testing of the system, independent of
the time of day and weather conditions, thereby greatly enhancing the time available for engineering. Fibre optics and
computer generated holograms (CGHs) are used to generate the necessary wavefront. We present the optomechanical
design, and discuss the expected accuracy, as well as tolerances in assembly and alignment.
Solar multiconjugate adaptive optics at the Dunn Solar Telescope
Show abstract
Solar observations are performed over an extended field of view and the isoplanatic patch over which conventional
adaptive optics (AO) provides diffraction limited resolution is a severe limitation. The development of multi-conjugate
adaptive optics (MCAO) for the next generation large aperture solar telescopes is thus a top priority. The Sun is an ideal
object for the development of MCAO since solar structure provides multiple "guide stars" in any desired configuration.
At the Dunn Solar Telescope (DST) we implemented a dedicated MCAO bench with the goal of developing wellcharacterized,
operational MCAO. The MCAO system uses two deformable mirrors conjugated to the telescope
entrance pupil and a layer in the upper atmosphere, respectively. The high altitude deformable mirror can be placed at
conjugates ranging from 2km to 10km altitude. We have successfully and stably locked the MCAO system on solar
granulation and demonstrated the MCAO system's ability to significantly extend the corrected field of view. We present
results derived from analysis of imagery taken simultaneously with conventional AO and MCAO. We also present first
results from solar Ground Layer AO (GLAO) experiments.
The optical tests for the E-ELT adaptive mirror demonstration prototype
Show abstract
The challenge of building extremely large telescope pushes forward the parallel ability to measure and test optical
components of large sizes. Here we present the optical bench setup for the Demonstration Prototype (DP) of the voice
coil controlled adaptive mirror M4AU of the E-ELT. A set of three devices has been chosen and used for the tests, whose
results are also shown. The performance demonstrated that this is a viable and trusted technology and the DP tests were
highly representative of the whole procedure that could be applied to the real, full size unit.
Adaptive optics systems for HARMONI: a visible and near-infrared integral field spectrograph for the E-ELT
Show abstract
HARMONI is a visible and near-infrared integral field spectrograph for the E-ELT. It needs to work at diffraction
limited scales. This will be possible thanks to two adaptive optics systems, complementary to each other. Both systems
will make use of the telescope's adaptive M4 and M5 mirrors. The first one is a simple but efficient Single Conjugate AO
system (good performance, low sky coverage), fully integrated in HARMONI itself. The second one is a Laser
Tomographic AO system (medium performance, very good sky coverage). We present the overall design of the SCAO
system and discuss the complementary between SCAO and LTAO for HARMONI.
Diffraction-limited upgrade to ARGOS: the LBT's ground-layer adaptive optics system
Show abstract
The Large Binocular Telescope (LBT) is now operating with the first of two permanently installed adaptive secondary
mirrors, and the first of two complementary near-IR instruments called LUCIFER is operational as well. The ARGOS
laser-guided ground-layer adaptive optics (GLAO) system, described elsewhere at this conference1, will build on this
foundation to deliver the highest resolution over the 4 arc min
wide-field imaging and multi-object spectroscopic modes
of LUCIFER. In this paper, we describe a planned upgrade to ARGOS which will supplement the Rayleigh-based GLAO
system with sodium laser guide stars (LGS) to fulfill the telescope's diffraction-limited potential. In its narrow-field
mode of 30 arc sec, LUCIFER will deliver imaging at the Nyquist limit of the individual 8.4 m apertures down to J band
and long-slit spectroscopy with resolution up to 40,000. In addition, the LBT Interferometer2 (LBTI) will cophase the
two apertures, offering imaging at the diffraction limit of the 22.8 m baseline at wavelengths from 1.2 to 20 μm. In the
first phase of the upgrade, a 10 W sodium LGS will be added to each half of the LBT, using the same launch telescopes
mounted behind the two secondary mirrors as the Rayleigh LGS. The upgrade will rely on other components of the
ARGOS infrastructure such as acquisition and guiding, and fast
tip-tilt cameras. New wavefront sensors will be added to
LUCIFER and LBTI. In the upgrade's second phase, the sodium and Rayleigh LGS will be used together in a hybrid
tomographic sensing system. This configuration will offer the advantage that a single tip-tilt star will continue to be
sufficient even for MCAO operation3, which is planned with LBT's LINC-NIRVANA instrument4,5.
Is ESO's adaptive optics facility suited for MCAO?
Show abstract
As of 2013, the ESO's VLT will be equipped with the Adaptive Optics Facility for Ground Layer and Laser Tomography
adaptive optics assisted imaging and spectroscopy, using a Deformable Secondary Mirror and four Laser Guide Stars.
Following the successful experience of the MAD demonstrator, we initiated a speculative study to evaluate the
performance gain obtained by implementing a type of Multi-Conjugate Adaptive Optics correction that benefits from the
unique features provided by the AOF. In this paper we present the basic concept and provide a first estimation of the
correction performance obtained in the near infrared.
Implementation and on-sky results of an optimal wavefront controller for the MMT NGS adaptive optics system
Show abstract
The MMT observatory has recently implemented and tested an optimal wavefront controller for the NGS
adaptive optics system. Open loop atmospheric data collected at the telescope is used as the input to a
MATLAB based analytical model. The model uses nonlinear constrained minimization to determine controller
gains and optimize the system performance. The real-time controller performing the adaptive optics close loop
operation is implemented on a dedicated high performance PC based quad core server. The controller algorithm
is written in C and uses the GNU scientific library for linear algebra. Tests at the MMT confirmed the optimal
controller significantly reduced the residual RMS wavefront compared with the previous controller. Significant
reductions in image FWHM and increased peak intensities were obtained in J, H and K-bands. The optimal PID
controller is now operating as the baseline wavefront controller for the MMT NGS-AO system.
Closed-loop tomographic control on HOMER wide-field AO bench: experimental results and identification issues
Show abstract
Adaptive Optics (AO) has a limited corrected field of view because of the anisoplanatism effect. Wide Field
AO (WFAO) concepts, such as Multi-Conjugate AO (MCAO), have been developed to overcome this limitation.
These complex WFAO systems raise critical challenges such as tomographic control and calibrations. We present
new results obtained in closed-loop configuration with the laboratory bench HOMER which is devoted to implementation
and validation of these WFAO concepts in the perspective of future VLT/ELT AO systems. Turbulence
is generated with rotating phase screens and multi-directional analysis is performed. Tomographic control relies
on Linear Quadratic Gaussian control (LQG). The correction can be applied thanks to two Deformable Mirrors
(DM). We also focus on calibration issues and models identification. We investigate in particular identification
of relative geometry of the wave front sensors, DM altitude and asterism and its impact on performance.
Development and performance of the EAGLE active optics LGS WFS refocusing system
Show abstract
We designed, developed, and tested a Variable Curvature Mirror (VCM) as an active refocusing system for the Laser
Guide Star (LGS) Wave Front Sensor (WFS) of the E-ELT EAGLE instrument [1]. This paper is the second of two from
our team on this R&D activity: Hugot et al. this conf. [2] presented the mirror design and performance simulations. Here,
we report on the fabrication integration, testing and performance of the VCM system. During this activity, we developed
all necessary parts for the VCM system: a metallic mirror, its housing and mounts, a computer-controlled pressure
system, an internal metrology, a testbench etc. The functional testing of the VCM system is successful: we can control
the internal pressure to less than 1 mBar, and measure the mirror displacement with a 100 nm accuracy. The mirror
displacement is a near-linear and well-simulated function of internal pressure for the desired range of focus. The intrinsic
optical quality of the mirror meniscus is well within the specifications. Once mounted in its housing, we observe
additional mechanical constraints for the current design that generate optical aberrations. We measured the amplitude of
the Zernike modes, and we showed that the axisymetric terms display a variation trend very similar to simulations, with
amplitude close to simulations. All these results are very promising for a design of focus compensation without any
moving part.
FFREE: a Fresnel-FRee Experiment for EPICS, the EELT planets imager
Show abstract
The purpose of FFREE - the new optical bench devoted to experiments on high-contrast imaging at LAOG - consists in
the validation of algorithms based on off-line calibration techniques and adaptive optics (AO) respectively for the
wavefront measurement and its compensation. The aim is the rejection of the static speckles pattern arising in a focal
plane after a diffraction suppression system (based on apodization or coronagraphy) by wavefront pre-compensation. To
this aim, FFREE has been optimized to minimize Fresnel propagation over a large near infrared (NIR) bandwidth in a
way allowing efficient rejection up to the AO control radius, it stands then as a demonstrator for the future
implementation of the optics that will be common to the scientific instrumentation installed on EPICS.
Vrala: designing and prototyping a novel high-efficiency actuator for large adaptive mirrors
Show abstract
The next-generation Extremely Large Telescopes adaptive optics systems
require high-order, long-stroke, quite large deformable mirrors.
Higher forces and greater actuator densities than the ones provided
by the current technology are needed, still maintaining its requests
in terms of accuracy and bandwidth. The electromagnetic "Vrala"
actuator can accomplish this very demanding goal. Based on a very
simple magnetic circuit, providing a compact device, it allows to
deliver a large force with very low power dissipations. With a typical
efficiency of about 7 N/W and an overall radius that allows actuator
separations as low as 25 mm, the deformable mirror can be actuated on
small spatial scales, and/or its thickness can be increased, in order to
simplify the manufacturing, with a little thermal impact. This paper
will mainly discuss the magnetic design of the proposed actuator, its
effects on the thermal response of the device as well as its behavior
in a closed loop control system - from the geometrical optimization
process to the dynamic performances. A prototype built accordingly
to the proposed design has been tested. The test set-up, as well as
the first set of the measured data, well matching the results of the
numerical simulations, will also be shown.
Simulations for diffraction limited near-infrared adaptive optics systems on the AOF
Show abstract
In this paper, we simulate different possibilities to upgrade the Adaptive Optics Facility (AOF) of the VLT, to reach the
diffraction limit in the near infrared. We present simulations of Ground Layer AO, Laser Tomography AO,
Multi-Conjugate AO, Dual AO and a hybrid system which is a simplified version of MCAO. We describe the strengths and
weaknesses of each approach and summarize the studies to be still carried out.
Optical designs with wide field-of-view adaptive optics for IMAKA of CFHT
Show abstract
As a ground-layer adaptive optics (GLAO) system can correct the wavefront errors caused by turbulence close to the
Canada-France-Hawaii telescope (CFHT), an intensive study is in progress to determine the feasibility and the
pertinence of equipping the CFHT of such a GLAO system. More specifically, the study concerns the implementation
of GLAO capabilities using a deformable mirror inserted into the optical path of an optical relay. The studied system
called IMAKA would be used both for the dynamic correction of the wavefront errors caused by air turbulence and the
increases of the telescope effective field of view. The objective pursued by IMAKA is to achieve a PSF with Full Width
at Half Maximum of less than 0.15" over a 1-degree field of view for extended wavebands within the spectral waveband
of 470 nm - 900 nm. This paper presents the main results of a study conducted by INO about the optical design
challenges of the IMAKA system. INO has proposed 4 different approaches for the realization of the system and made
preliminary optical designs for each of them. The science camera and deformable mirror in the proposed designs are
located below the Cassegrain environment for three of the proposed configurations and between the primary mirror and
the top ring for the fourth design. In all the proposed configurations, the effective focal length of the telescope with the
added correction relay is about 20.63 m for a working focal ratio of about 5.74. The design configurations included in
this paper have achieved nearly diffraction limited performances with a deformable mirror having a diameter inferior to
0.5 m and flat or mild curvature nominal shape. Based on our preliminary optical design and performance analysis with
the 4 optical design approaches, it seems possible to achieve most of the IMAKA requirements.
An update of the on-sky performance of the layer-oriented wavefront sensor for MAD
Show abstract
The Multi-conjugate Adaptive optics Demonstrator, MAD, successfully demonstrated on sky the MCAO technique
both in Layer Oriented and Star Oriented modes. As results of the Guaranteed Time Observations in
Layer Oriented mode quality astronomy papers have been published. In this paper we concentrate on the
instrumentation issues and technical aspects which stay behind this success.
Analysis of adaptive optics control for the Advanced Technology Solar Telescope
Show abstract
Large aperture solar telescopes, such as the 4 meter aperture Advanced Technology Solar Telescope (ATST),
depend on high order adaptive optics (AO) to achieve the telescope's diffraction limited resolution. The AO
system not only corrects incoming distortions introduced by atmospheric turbulence, its performance also plays
a critical role for the operation of other subsystems and affects the results obtained by downstream scientific
instrumentation. For this reason, robust and optimal operation of the AO system is vital to maximize the
scientific output of ATST.
In order to optimize performance, we evaluate different strategies to obtain the control matrix of the AO
system. The dependency of AO performance on various control parameters, such as different system calibration
and reconstruction schemes, is analyzed using an AO simulation tool. The AO simulation tool provides a realistic
solar AO system simulation and allows a detailed evaluation of the performance achieved by different calibration
and reconstruction methods.
The results of this study will guide the optimization of the AO system during design and operations.
The METIS AO system: bringing extreme adaptive optics to the mid-IR
Show abstract
METIS (Mid-infrared E-ELT Imager and Spectrometer) is the
mid-infrared instrument proposed for the European
Extremely Large Telescope (E-ELT). METIS will be the first instrument in the mid-IR that will actually require an
Adaptive Optics system in order to reach a performance close to the diffraction limit. Extending Adaptive Optics for the
mid-IR from the current generation of telescopes to 30-42 meter telescopes is technically challenging, but appears at first
sight significantly easier than at visible and near infrared wavelengths.
Adaptive Optics has been demonstrated to deliver Strehl Ratios exceeding 95% on 6-8 meter class telescopes at 10
microns, but achieving this performance on E-ELTs under normal observation conditions, requires that several higher
order effects are taken into account. The performance of a mid-IR AO system drops significantly if refractivity effects
and atmospheric composition variations are not compensated. Reaching Strehl Ratios of over 90% in the L, M and N
band will require special considerations and will impact the system design and control scheme of AO systems for mid-IR
on ELTs.
The METIS instrument has finalized its preliminary design phase and in this paper we present the results of our
performance estimates of the METIS AO system. We have included the effects of refractivity and composition
fluctuations on the performance of the AO system and we have investigated how these effects impact the science cases
for mid-IR instrumentation on an ELT.
First light AO (FLAO) system for LBT: performance analysis and optimization
Show abstract
We will present in this paper the performance analysis and optimization of the First Light AO (FLAO) system
of the Large Binocular Telescope (LBT). The system comprises an adaptive secondary mirror (ASM) with 672
actuators (LBT672a unit) and a pyramid wavefront sensor (PWFS) with adjustable sampling of the telescope
pupil from 30×30 down to 4×4 subapertures. The performances have been estimated by means of end-to-end simulations,
scanning a range of reference star magnitudes and looking for the optimal set of parameters maximizing
the on-axis Strehl Ratio. Specific additional error sources have been accounted for and analyzed separately, such
as mis-registration errors, mis-calibration issues, and the effect of telescope vibrations. Taking into account the
considered error sources we defined the baseline and goal performances of the FLAO system. The acceptance test
of the FLAO system took place in December 2009, demonstrating actual FLAO performances between baseline
and goal estimates. The commissioning of the FLAO system to the LBT telescope is currently ongoing until
December 2010.
Demonstration of a robust curved carbon fiber reinforced polymer deformable mirror with low surface error
Show abstract
Carbon fiber reinforced polymer (CFRP) composites provide several advantages as a substrate for thin-shell adaptive
secondary mirrors, including high stiffness-to-weight ratio and low coefficient of thermal expansion (CTE). We have
addressed some of these concerns using a prototype CFRP mirror under actuation. Using 4D and Newton interferometry,
we present measurements of surface quality at a range of temperatures. Under actuator relaxation at room temperature,
its surface error is low (92 nm RMS) and dominated by edge curvature. This error is reduced further under best actuator
correction to 43 nm RMS, placing it into consideration for use in near-IR astronomy. The low surface error internal to
the outer ring of actuators - 17 nm RMS at 60°F and 33 nm RMS at 20°F - suggests that larger mirrors will have a
similar figure quality under actuator correction on ground-based AO systems. Furthermore, the actuator forces required
to correct the figure are small compared to the dynamic range of voice coil actuators (~0.1 N). In addition, surface
roughness is characterized to address the effects of high spatial frequency errors.
Real-time control for Keck Observatory next-generation adaptive optics
Show abstract
The next generation adaptive optics systems for large telescopes will be complex systems far larger, more complex, and
with higher performance than any currently installed. This requires adopting new algorithms, technologies, and
architectures. The Keck next generation adaptive optics (NGAO) system requires real-time wavefront reconstruction
and tomography given input from 7 laser and 3 natural guide stars. Requirements include 2 KHz atmospheric sampling,
tomographic atmosphere estimation, and control for 5 deformable mirrors. We take advantage of the algorithms'
massive parallelism and realize it on a massive array of FPGAs, GPUs, and multi-core CPUs. This paper presents the
current design and analysis of the NGAO system.
Adaptive optics system for the IRSOL solar observatory
Renzo Ramelli,
Roberto Bucher,
Leopoldo Rossini,
et al.
Show abstract
We present a low cost adaptive optics system developed for the solar observatory at Istituto Ricerche Solari
Locarno (IRSOL), Switzerland. The Shack-Hartmann Wavefront Sensor is based on a Dalsa CCD camera with
256 pixels × 256 pixels working at 1kHz. The wavefront compensation is obtained by a deformable mirror with
37 actuators and a Tip-Tilt mirror. A real time control software has been developed on a RTAI-Linux PC.
Scicos/Scilab based software has been realized for an online analysis of the system behavior. The software is
completely open source.
SAM sees the light
Show abstract
We present a progress report on the SOAR Adaptive Module, SAM, including some results of tests of the Natural
Guide Star mode: image correction in the visible, performance estimates, and experiments with lucky imaging.
We have tested methods to measure the seeing and the AO time constant from the loop data and compared
the results to those of the stand-alone site monitor. Measurements of the instrument throughput and telescope
vibrations are given. We report progress on the Laser Guide Star system implementation, including tests of the
UV laser, test of the beam transfer optics with polarization control. We present the designs of the laser launch
telescope and laser wavefront sensor.
Testing the VLT AO facility with ASSIST
Show abstract
The testing and verification of ESO Very Large Telescope Adaptive Optics Facility (VLT-AOF) requires new and
innovative techniques to deal with the absence of an intermediate focus on the telescope. ASSIST, The Adaptive
Secondary Setup and Instrument STimulator, was developed to provide a testing facility for the ESO AOF and will allow
off-telescope testing of three elements of the VLT Adaptive Optics Facility; the Deformable Secondary Mirror (DSM)
and the AO systems for MUSE and HAWK-I (GALACSI and GRAAL). ASSIST will provide a full testing environment
which includes an interferometric testing mode for the DSM, an
on-axis testing mode with a single wavefront sensor and
full operation testing modes for both the AO systems. Both natural as well as laser guide stars will be simulated under
various asterisms and a realistic turbulent atmosphere will be provided for varying atmospheric conditions. ASSIST
passed its final design review and is now being manufactured, integrated and tested and will be operational in mid 2011,
in time for first testing with the DSM.
Performance of Subaru adaptive optics system AO188
Show abstract
Subaru adaptive optics system (AO188) is an 188-elements curvature sensor adaptive optics system that is operated
in both natural and laser guide star modes. AO188 was installed at Nasmyth platform of the Subaru
telescope and it has been successfully operating in the natural guide star mode since October 2008. The performance
of AO188 in the natural guide star mode has been well verified from on-sky data obtained with the infrared
camera and spectrograph (IRCS). Under normal seeing condition, AO188 achieves K-band Strehl ratio between
60% and 70% using R = 9.0 magnitude natural guide stars and it works well with faint guide stars down to
R = 16.5 magnitude. We measured the FWHM and Strehl ratio of stellar images in globular clusters and found
that the isoplanatic angle is approximately 30 arcsec. In this paper, we describe an overview of the operation
procedure for AO188, as well as its performance such as angular resolution, Strehl ration, and sensitivity gain
for detecting faint objects.
GMT adaptive secondary design
Show abstract
The GMT adaptive secondary mirror (ASM) is based on a "segmented" concept following the primary segment layout:
seven 1.05m diameter circular, independent adaptive mirrors are fed by the primaries and focus to the main telescope
focal stations. The adaptive unit's design is based on the consolidated thin mirror, contactless technology already
employed in several units (MMT, LBT, Magellan, VLT and one of the proposed E-ELT M4 designs), but nevertheless
the mirror's topology reveals several design challenges. In particular, the off-axis units are strongly aspheric and
therefore they require aspheric shaping of both thin mirror surfaces and of the thick reference body. The strong tilt of the
off-axis units forced us to consider a peculiar fine positioning hexapod design, maximizing its stiffness and also
implementing a special design of the last three rings of actuators to remain within the prescribed obstruction. From the
control point of view, the actuator density of the adaptive mirrors is remarkably lower than in all previous units: 672
actuators with 36mm spacing compared to 30mm typical separation adopted so far. This choice is validated by static and
dynamic performance computation though a sophisticated numerical simulator based on a full state space model
incorporating mechanics, control and fluid dynamics. The control system fulfills the dimensional constraints of the unit.
The design has completed the feasibility phase, including the cost estimate. The choice of making the GMT adaptive
secondary mirrors similar to the already existing ones strongly reduces the implementation risks and allows shortening
the remaining design path.
A portable solar adaptive optics system: software and laboratory developments
Show abstract
We present our recent process on a portable solar adaptive Optics system, which is aimed for diffraction-limited imaging
in the 1.0 ~ 5.0-μm infrared wavelength range with any solar telescope with an aperture size up to 1.6 meters. The realtime
wave-front sensing, image processing and computation are based on a commercial multi-core personal computer.
The software is developed in LabVIEW. Combining the power of multi-core imaging processing and LabVIEW parallel
programming, we show that our solar adaptive optics can achieve excellent performance that is competitive with other
systems. In addition, the LabVIEW's block diagram based programming is especially suitable for rapid development of
a prototype system, which makes a low-cost and high-performance system possible. Our adaptive optics system is
flexible; it can work with any telescope with or without central obstruction with any aperture size in the range of 0.6~1.6
meters. In addition, the whole system is compact and can be brought to a solar observatory to perform associated
scientific observations. According to our knowledge, this is the first adaptive optics that adopts the LabVIEW high-level
programming language with a multi-core commercial personal computer, and includes the unique features discussed
above.
SAMI: the SCAO module for the E-ELT adaptive optics imaging camera MICADO
Show abstract
SAMI, the SCAO module for the E-ELT adaptive optics imaging camera MICADO, could be used in the first
years of operation of MICADO on the telescope, until MAORY is operational and coupled to MICADO. We
present the results of the study made in the framework of the MICADO phase A to design and estimate the
performance of this SCAO module.
Visible and infrared multispectral illumination concept based on Galilean collimation systems: IACATS illumination source
Show abstract
A LED based illumination system in which five Galilean collimation systems have been used is reported
on. It is part of a turbulence simulator for the evaluation of on ground telescopes instrumentation developed
by INTA (optics) and LIDAX (opto-mechanics) for the IAC called IACATS. The illumination requirements
(some visible and infrared lines) allow the use of five different LEDs (red, green, blue and two infrareds). In
order to optimize the illumination level of each wavelength, a Galilean collimating optical configuration was
constructed for each wavelength channel.
The IACATS instrument simulates a scene consisting of a set of different binary stars simulating the
required angular separation between them, ant their spectral characteristics. As a result, a visible and infrared
multi-spectral illumination system has been integrated as a part of the turbulence simulator, and the features
(opto-mechanical) and illumination characteristics are described in the following lines.
IACATS AIV: AIV process for a versatile turbulence simulator
Show abstract
IACATS is an atmospheric turbulence, stars and telescope simulator for the evaluation of on ground
telescopes instrumentation developed by INTA (optics) and LIDAX
(opto-mechanics) for the IAC (Instituto
de Astrofísica de Canarias).
Three telescopes have been simulated, matching the f number, focal plane, and optical interface of the
actual telescopes. An optical breadboard was designed and built containing the required opto-mechanics for
simulating the telescopes, and various levels of turbulence required.
In addition to the telescope simulator optics, a set of three phase plates have been procured and
conveniently combined in order to reproduce the atmospheric turbulence required by the IAC. A wave front
sensor has been also included in order to evaluate the deformation that the phase plates, or the simulated
turbulence, produce in the wave front coming from the illumination system and star simulator. Finally, a
specific illumination system was developed including different working wavelengths in order to fulfil the
requirements. The description of the illumination system itself has been done in a separate publication.. In the
following lines, the characteristics of the IACATS instrument as well as the results obtained from the AIV
(Assembly and Integration Verification) process are reported on.
Tip/tilt offload of Subaru AO188 by telescope secondary mirror
Show abstract
A tip/tilt off-load function from AO188 deformable mirror mount to Subaru telescope infrared secondary mirror
has been implemented and tested. The function is effective to reduce the influence of strong background pattern
at thermal infrared wavelengths. We describe the function and report the test results in this paper.
Design and expected performances of the SCAO-WFS module of SIMPLE, the high-resolution near-infrared spectrometer for E-ELT
Show abstract
We present and discuss the design and expected performances of the SCAO-WFS module of SIMPLE, the highsd
resolution near-infrared spectrometer for the E-ELT which is designed to operate in the wavelengths range 0.84-2.5μm
with an entrance slit width of 27mas which yields a spectral resolving power of R=130,000. We analyze both pyramid
and SH wave-front sensors operating at near-infrared wavelengths (1-2 μm). The main results can be summarized as
follows.
- Good levels of AO correction can only be achieved within a few arc-sec of the reference star. The primary
applications of SCAO correction are therefore observations where the science object is compact and bright enough
to be used as reference star, feeding the WFS via a beam-splitter. We concentrate on a WFS operating at nearinfrared
wavelengths because many of the scientific targets of SIMPLE are intrinsically very red.
- The pyramid WFS provides better performances than the SH, because it is less affected by aliasing errors.
- The quality of AO correction is almost independent on the wavelength at which the wave-front is sensed. Therefore,
we simplify the design the WFS module by not including the K-band, i.e. operating in the 1.0-2.1μm range.
Extension to shorter wavelengths is also possible but requires exchanging the atmospheric dispersion compensator.
- Using a pyramid WFS with 84x84 sub-apertures one can achieve remarkably high values of light-concentration in
the slit, i.e. ~70% in K and ~40% at 0.9μm.
- The limiting magnitude for the 84×84 WFS is about 13.5+2.5•log(η), where η is the fraction of stellar light sent to
the WFS by the beam-splitter.
- Somewhat fainter limits, i.e. magnitudes ~14.0+2.5•log(η), can be achieved by changing the camera optics of the
WFS and sampling 42×42 sub-apertures.
Experimental validation of a numerical model for non-contact, massively actuated deformable adaptive mirrors
Mauro Manetti,
Marco Morandini,
Paolo Mantegazza,
et al.
Show abstract
The validation of the multidisciplinary model of a deformable, massively actuated adaptive mirror is presented.
The related experimental correlations are focused on an adaptive shell with 45 non contacting voice coils actuated
points, dubbed P45, that was developed as an engineering verification prototype for the LBT adaptive
secondary mirrors. A description of the multi physics model is followed by the results obtained simulating actual
experimental tests and by their correlation with the related true measures. The significance of various modeling
details and their impact on the correlation is discussed. The results show a remarkable match between numerical
and experimental data.
Lucky imaging and adaptive optics on 10-m class telescopes: a real promise for diffraction limited imaging in the visible?
Show abstract
Traditionally thought as alternatives of each other, it has not been until very recently when Adaptive Optics (AO)
and lucky imaging (LI) have been put to work together to achieve angular resolutions in the visible wavelengths
comparable to those acquired with an ideal telescope. In this work the mutual benefits of combining fast frame
selection (a.k.a. Lucky Imaging, LI) with Adaptive Optics (AO) on a 10-m class telescope are investigated by
means of detailed Monte-Carlo numerical simulations. We investigate the expected image quality by looking at
the Strehl Ratio (SR) at the optical R and I bands (around 650 and 800nm, respectively) and the potential of
the technique to conduct high-contrast imaging. From our numerical simulations we are able to assess whether
there is a net gain in the high-contrast capabilities when applying wavelet-based filtering techniques. As a test
bench for what we should expect by moving on a 10-m class telescope we present recent results achieved with
AO+LI at the 4-m William Herschel Telescope (WHT) by looking at the brown dwarf binary GJ569Bab.
Adaptive optics simulation with mechanically motivated basis functions
Show abstract
For high accuracy simulation of Adaptive Optics (AO), multi-conjugate AO (MCAO), and ground layer AO (GLAO)
analytic models have proven to be of significant importance. Usually, these models employ a finite set of Zernike basis
functions that allow replacing point-by-point computation of phase maps by algebraic manipulation of basis function
coefficients. For closed loop simulation of AO systems it is essential to consider the spatial and temporal dynamics of
deformable mirrors and wavefront sensors. In this case, simulations with Zernike basis functions have several drawbacks.
First of all, they become computationally intractable when high order and high frequency behavior is analyzed. Additionally,
the spatial dynamics of deformable mirrors cannot be approximated well by Zernike functions when mechanical
constraints are considered.
In this paper, a set of orthogonal basis functions formed by spatial eigenmodes of deformable mirrors is proposed for
simulation of large scale AO systems. It is shown that an analytic approximation of deformable mirror bending modes can
be derived by solving a partial differential equation (PDE) and an inclusion of appropriate boundary conditions. Three sets
of basis functions from different boundary conditions are studied in detail: the cases of a clamped edge, free edge, and
flexible support of a circular mirror plate. The basis functions are compared to the Zernike functions and their mathematical
properties are discussed.
Multilayered temporally evolving phase screens based on statistical interpolation
Show abstract
Simulation of the dynamic effects of atmospheric turbulence assists in understanding, testing and effective implementation
of adaptive optics systems. Statistical interpolation technique helps in retaining the spatial turbulence
statistics when atmospheric phase screens are required to be moved by non-integer multiples of the grid spacing.
We applied statistical interpolation in the simulation of temporally evolving phase screens using the multilayer
model of atmospheric turbulence. A comparison of the statistical method with bilinear interpolator and random
midpoint displacement method is presented. It is shown that underestimating Fried's parameter (r0) in the
interpolation leads to large errors and hence it is appropriate to choose a little larger value of r0 than estimated
from the phase screens.
Optimizing the modal index of Zernike polynomials for regulated phase screen simulation
Show abstract
Simulations of optical wavefronts propagating through the atmosphere are widely used in the design and testing of
adaptive optics systems. Phase screens are defined by their spatial and temporal statistics. In many applications,
a controlled production of phase is necessary. A linear combination of normalized Zernike polynomials can be
used for the generation of phase screens through the computation of Zernike moments following Kolmogorov
turbulence spectrum. In this paper, a technique for controlled production of normalized phase screens using a
known Fried's parameter, r0 is proposed by taking the advantage of the fact that with increasing radial index (n)
of Zernike polynomials, the spatial frequency increases. We arrived at an empirical relation between the index
interval of Zernike polynomials and r0. At large value of 'n', there is saturation in the minimum achievable r0
value.
Multiconjugate adaptive optics with plenoptic cameras and the Fourier transform reconstructor
Show abstract
Multi-Conjugate Adaptive Optics (MCAO) will play a key role in future astronomy. Every Extremely Large
Telescope (ELT) is being designed with its MCAO module, and most of their instruments will rely on that kind of
correction for their optimum performance. Many technical challenges have to be solved in order to develop MCAO
systems. One of them, related to its use on ELT's, is to find fast algorithms to perform the reconstruction at the
required speed. For that reason we have been studying the application of the Fourier Transform Reconstructor
(FTR) to MCAO. We use the Fourier Slice Theorem in order to reconstruct the atmospheric volume. The process
consists on reconstructing "slices" of atmosphere, taking 1D-FFT's of the different projections to build a 2D
Fourier space that is inverse-transformed to build the reconstructed slice. The advantage of using the FTR is
that this algorithm gives us directly the Fourier Transform of the projections, speeding up the process. To do a
good reconstruction it is necessary to know the height at which the laser guide star is focused, and we propose
to use a plenoptic camera to get this information, that we use together with the available information relative to
the atmosphere we are reconstructing, C2n, to weight the inverse-transforms and obtain a better estimate. The
height is obtained in real-time, a very important advantage for the reconstruction. We present the preliminary
results of our MCAO simulations and the configuration of the plenoptic camera that could be applied to an ELT
Modeling the adaptive optics systems on the Giant Magellan Telescope
Show abstract
Modeling adaptive optics (AO) systems is crucial to understanding their performance and a key aid in their
design. The Giant Magellan Telescope (GMT) is planning three AO modes at first light: natural guide star AO,
ground-layer AO and laser tomography AO. This paper describes how a modified version of YAO, an open-source
general-purpose AO simulation tool written in Yorick, is used to simulate the GMT AO modes. The simulation
tool was used to determine the piston segment error for the GMT. In addition, we present a comparison of
different turbulence simulation approaches.
Simulations of the extreme adaptive optics system for EPICS
Show abstract
EPICS is a project for a high contrast imaging instrument dedicated to direct imaging of exoplanets with the
European Extremely Large Telescope. Its conceptual design study phase has finished at the early 2010, and
we show here its end-to-end extreme adaptive optics simulation results. The simulations have been made using
conventional, well-known but numerically intensive computation techniques (full Fourier diffraction model of a
WFS and wavefront reconstruction with matrix-vector-multiplication). Many error sources important for XAO
are considered: chromaticity effects, M1 segment mis-figure, pupil rotation, WFS misregistration, telescope jitter
and spiders. The results confirm that a raw contrast of 10-5 is reached at 20 mas, and 10-7-10-6 at 200-500 mas.
This is in agreement with our analytic estimations and EPICS
top-level requirements.
The CAOS problem-solving environment: recent developments
Show abstract
We present recent developments of the CAOS problem-solving environment (PSE), an IDL-based software tool
whose original aim was to define and simulate as realistically as possible the behavior of a generic adaptive
optics (AO) system -from the atmospheric propagation of light, to the sensing of the wave-front aberrations
and the correction through a deformable mirror- but which results in a widely more general tool now. In
fact, the different developments made through the last years result in a very versatile numerical tool complete
of a global graphical interface (the CAOS Application Builder), a general utilities library (the CAOS
Library), and different packages dedicated to a wide range of astronomical-optics-related scientific topics: the
original package designed for end-to-end AO system simulations (the Software Package CAOS), an image simulation/
reconstruction package with interferometric capabilities (the Software Package AIRY), an extension of
the latter specialized for the LBT instrument LINC-NIRVANA (the Software Package AIRY-LN), an ad hoc
package dedicated to the VLT instrument SPHERE (the Software Package SPHERE), and an embedment of the
analytical AO simulation code PAOLA (the Software Package PAOLAC).We present the status of the whole CAOS
PSE, together with the most recent developments, and plans for the future of the overall tool.
Modeling adaptive optics for the segmented aperture of the GMT
Show abstract
We present expected performance for the Giant Magellan Telescope (GMT) adaptive optics system. Using a
custom adaptive optics modeling code developed at the University of Arizona, we are able to simulate the various
aspects of atmospheric turbulence, wavefront sensing, and adaptive correction for the specific geometry of the
GMT AO system. This allows us to explore the design space of the GMT and determine the performance of the
system for various adaptive optics modes, including Ground-Layer AO. We present results showing the effect of
the segmented aperture on AO performance, and discuss strategies for sensing and correction with the GMT
aperture.
An atmospheric turbulence generator for dynamic tests with LINC-NIRVANA's adaptive optics system
Show abstract
LINC-NIRVANA[1] (LN) is an instrument for the Large Binocular Telescope[2] (LBT). Its purpose is to combine the light
coming from the two primary mirrors in a Fizeau-type interferometer. In order to compensate turbulence-induced
dynamic aberrations, the layer oriented adaptive optics system of LN[3] consists of two major subsystems for each side:
the Ground-Layer-Wavefront sensor (GLWS) and the Mid- and High-Layer Wavefront sensor (MHLWS). The MHLWS
is currently set up in a laboratory at the Max-Planck-Institute for Astronomy in Heidelberg. To test the multi-conjugate
AO with multiple simulated stars in the laboratory and to develop the necessary control software, a dedicated light
source is needed. For this reason, we designed an optical system, operating in visible as well as in infrared light, which
imitates the telescope's optical train (f-ratio, pupil position and size, field curvature). By inserting rotating surface etched
glass phase screens, artificial aberrations corresponding to the atmospheric turbulence are introduced. In addition,
different turbulence altitudes can be simulated depending on the position of these screens along the optical axis. In this
way, it is possible to comprehensively test the complete system, including electronics and software, in the laboratory
before integration into the final LINC-NIRVANA setup. Combined with an atmospheric piston simulator, also this effect
can be taken into account. Since we are building two identical sets, it is possible to feed the complete instrument with
light for the interferometric combination during the assembly phase in the integration laboratory.
Simulation of low-order AO performance on LAMOST
Show abstract
Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) is a large aperture and wide field telescope
whose image quality requirement at Xinglong station is 80% light energy within 2 arcsecond. In fact, the designed image
quality of the central field of view is diffraction limited under optical wavelength. Due to the 60m long light path and
poor natural seeing, dome seeing and other errors, the image quality is averaged about 0.5arcsecond to 1 arcsecond. We
consider deploying a low-order adaptive optics system on LAMOST to improve seeing conditions and the corresponding
image quality. Based on the sounding balloon results on Xinglong Station, we make the numerical simulation of the AO
performance and get Fried parameter, the final point spread function (PSF) characteristics of LAMOST including Strehl
ratio, full width at half- maximum (FWHM), and the residual variance.
Performance evaluation of a SCAO system for a 42-m telescope using the pyramid wavefront sensor
Show abstract
We perform simulations of a single-conjugated adaptive optics (SCAO) system for an E-ELT-like telescope
using a pyramid wavefront sensor (PWFS) and an on-axis NGS. The advantage of this WFS has already been
demonstrated, being currently preferred in many AO systems where high signal sensitivity is critical. The main
objective of this work is to evaluate the performance of such SCAO system under different control parameters
(loop gain, modulation, truncated SVD mode), sensing wavelengths, atmospheric coherence scales and NGS
magnitudes. Always adopting K as the science band, we have verified that the overall performance tends to
be poorer as the sensing wavelength becomes shorter. The loop gain optimal range is dependent on the SVD
truncation threshold used to build the command matrix, and a
non-modulated PWFS produces in general poorer
results when compared to modulated cases, being this especially true for the R- sensing band. The default
atmospheric model adopted was a von Karman with r0=0.13m (at 500nm) and outer scale of 25m, but poorer
and better seeing conditions have also been tested. The long-exposure Strehls are better in larger modulations.
The telescope pupil has a central obstruction of 28% but no spiders were included. We also show results for the
incidence of different photon fluxes at the PWFS detector.
Modeling the spatial PSF at the VLT focal plane for MUSE WFM data analysis purpose
Show abstract
MUSE is the Multi Unit Spectroscopic Explorer, an AO-assisted integral field spectrograph for visible and
near-IR wavelengths which is planned to be commissioned at the UT4 of the Very Large Telescope in 2012.1 We
present the status on the modeling of the spatial PSF at the UT focus and its Field-of-View (FoV) and spectral
variations. Modeling these variations and studying their implications is a cornerstone for some MUSE data
analysis and processing problems such as fusion, source extraction and deconvolution of MUSE datacubes.
In Wide Field Mode (WFM, 1 square arc-minute FoV, 0.2 arcsec spatial sampling), MUSE can operate
without Adaptive Optics (AO) correction or with a Ground Layer Adaptive Optics facility aimed at providing
an almost uniform correction over a large field of view. In Narrow Field Mode (7.5 square arcseconds FoV, 0.025
arcsec spatial sampling) MUSE will make use of a Laser Tomography Adaptive Optics reconstruction, implying
stronger spatial variations. By using the adaptive optics simulation tool PAOLA, we simulate in WFM the
spatial PSF as a function of atmospheric turbulence parameters, observed wavelengths, AO mode and position
in the field of view. We then develop a mathematical model fitting the generated data which allows, with a small
number of parameters, to approximate the PSF at any spatial and spectral position of MUSE datacube. Finally,
we evaluate the possibility to estimate the model parameters directly from the (future) MUSE data themselves.
Dimensioning the Gravity adaptive optics wavefront sensor
Show abstract
We present the adaptive optics simulations we have performed to dimension the Gravity adaptive optics wavefront
sensor. We first computed the optimal WFS bandpass, depending on the sampling frequency, detector readout
noise and reference source colour/temperature. We then performed adaptive optics simulations with the YAO
simulation tool for different WFS parameters (number of subpupils, number of pixels per subpupil, loop frequency,
reference source magnitude, etc). Results demonstrate that the Gravity adaptive optics top-level requirements
can be fulfilled with a 9×9 subaperture Shack-Hartmann with 4 pixels per subaperture using an H+K filter, a
larger filter being recommended for sources bluer than 770 K reference source of the Galactic Centre.
Atmosphere and telescope simulator for new adaptive optics methods development
Show abstract
The IACAT (IAC Atmosphere and Telescope) Simulator is an Optical Ground Support Equipment which simulates
atmospheric turbulence and reproduces the performance of three very different telescopes: GTC and WHT, located at
the Observatorio Del Roque de los Muchachos in La Palma (Canary Islands), and OGS which is located at the
Observatorio Del Teide in Tenerife (Canary Islands). Its mission is to provide Scientists with the same measurement
conditions as the real telescope but in a friendly laboratory environment, to assist in the development of new adaptive
optics methods based on FPGAs.
The most important telescope characteristics are simulated, such as f number, pupil size and position, magnification,
central obscuration, etc. Up to 13 stellar objects can be created, individually or as binary stars with specific angular
separations down to miliarcseconds.
For the atmosphere simulation, it allows the creation of three different turbulence layers concurrently with different
altitude and wind speed ranges.
Adaptive optics for satellite-to-ground laser communication at the 1m Telescope of the ESA Optical Ground Station, Tenerife, Spain
Show abstract
We present the setup including optics and components, the reconstruction scheme and performance estimations
of an Adaptive Optics (AO) system implemented at the 1m telescope of the ESA Optical Ground Station (OGS),
Observatorio del Teide, Tenerife. The system will be used to improve the signal-to-noise ratio of satellite to ground
laser communications. It operates with coherent laser communication systems at 1064nm. The wavefront sensor
is an 88-element Shack-Hartmann-sensor (11 subapertures across the pupil), matched to a 12×12 actuator
"Multi-DM" membrane deformable mirror (DM). The system is able to remove a large part of the turbulence-induced
and static wavefront errors by using more than 90 degrees of freedom ("modes"). Due to a special high speed
infrared camera, the control loop can run at speeds up to 20 kHz, achieving a 0db bandwidth of about 500Hz,
depending on the received laser power.
ARGOS: a laser star constellation for the LBT
Show abstract
ARGOS is an innovative multi-star adaptive optics system being built for use with LUCIFER on the Large Binocular
Telescope (LBT). LUCIFER is a wide field imager and multi-object spectrograph. Using a constellation of laser guide
stars permits PSF correction over a wide field in exchange for a relatively small sacrifice in achievable correction. The
laser constellation consists of three stars per each of the two eyes of the LBT. The stars are nominally positioned on a circle
2' in radius, but each star can be moved by upto 0.5' in any direction. Nd:YAG (SHG) lasers from InnoLas Laser GmbH
are used to create the green (532nm) laser stars, and have an output above 18 W each at the planned pulsing frequency of
10kHz. The lasers are launched using a 40cm telescope and focused at a height of 12 km. The laser system is designed
to be optically simple yet configurable. It also provisions for a central sodium laser to be installed later. We detail the
characteristics of the laser system and the current state of its development.
Noise reduction in the centroiding of laser guide star spot pattern using thresholded Zernike reconstructor
Show abstract
Centroiding inaccuracies contribute to most of the wavefront reconstruction error in a Shack Hartmann sensor
based adaptive optics system. These errors primarily occur due to the presence of photon noise, readout noise,
finite background and strong scintillations. Elongation of the spots in the case of large apertures while using Laser
guide star as reference makes the situation further worse. A denoising procedure based on thresholded Zernike
reconstructor and pattern matching is suggested in this paper to largely overcome these problems. Individual
spot pattern images are reconstructed using Zernike polynomials and matched with ideal spot pattern without
distortion to arrive at accurate local centroid positions.
Classical adaptive optics: disturbance rejection control
Jean-Pierre Folcher,
Andrea Abelli,
André Ferrari,
et al.
Show abstract
This paper addresses the residual wavefront variance minimization by means of a linear quadratic gaussian
control methodology. The proposed approach emphasizes the ability of the adaptive optics loop to reject the
atmospheric aberration. We derive a diagonal state space system which clearly separates the dynamics of the plant
(deformable mirror & wavefront sensor) from the disturbance dynamics (atmospheric model). This representation
facilitates the numerical resolution of the problem. A frequency analysis is carried out to check performance
and robustness specifications of the multiple-input multiple-output feedback system. The effectiveness of the
approach is demonstrated through numerical experiments using wavefronts generated with the Software Package
CAOS.
Simulation of wavefront measurement and tomography for Extremely Large Telescope
Show abstract
The control of AO systems dedicated to ELT is a difficult problem related to the large number of degrees of freedom. The
standard and most used adaptive optics AO control starting from the integrator to the LQG are not useful in such a case.
In fact, for future Extremely Large Telescope (ELT's) the number of degrees of freedom is very large related to the large
diameter of the ELT's and the emergence of new architectures for the AO systems. So that the necessary computational
power for real time control RTC on such systems is currently unattainable when using these control methods.
In this paper we present an Adaptive Optics E2E simulator which includes a very fast wave front reconstruction which is
dedicated for the Extremely Large Telescope. This code takes advantages of the SOY library, where we build the interaction
and reconstruction matrix in a sparse format. Based on a script for solving linear systems by conjugate gradient with Jacobi
preconditioner , our reconstruction matrix is computed very fast.
Moreover, we present the reconstruction results for a 42 m and so the characterization time of the code.
Multiple field-of-view MCAO for a Large Solar Telescope: LOST simulations
Show abstract
In the framework of a 4m class Solar Telescope we studied the performance of the MCAO using the LOST
simulation package. In particular, in this work we focus on two different methods to reduce the time delay
error which is particularly critical in solar adaptive optics: a) the optimization of the wavefront reconstruction
by reordering the modal base on the basis of the Mutual Information and b) the possibility of forecasting the
wavefront correction through different approaches. We evaluate these techniques underlining pros and cons of
their usage in different control conditions by analyzing the results of the simulations and make some preliminary
tests on real data.
Implementation of type-II tip-tilt control in NFIRAOS with woofer-tweeter and vibration cancellation
Show abstract
In a previous paper, we have proposed to implement a type-II controller in NFIRAOS, the Narrow Field Infra Red
Adaptive Optics System for the Thirty Meter Telescope. Type-II control enables increased tip-tilt rejection, which, for a
given error budget, translates into increased sky-coverage. Our proposed type-II controller is a cascade of two
integrators, a gain and a lead filter. The correction is then split between the tweeter (the deformable mirror surface) and
the woofer (a tip-tilt stage that holds the deformable mirror) using high and low pass filters. So far, we had only
characterized this controller in the continuous domain, where the discrete nature of the real-time computer part is
approximated by continuous functions (Laplace analysis). In this paper, we discuss the discrete implementation, with
particular focus on a) anti-windup, to robustly deal with temporary saturations, and b) low sampling rates, where
frequency warping and aliasing may occur in the discretization process. The implementation is tested in a hybrid
Simulink model, where continuous and discrete processes are properly implemented using continuous or discrete blocks,
respectively, and the performance is compared with the performance predicted by the continuous domain analysis. An
effective saturation handling strategy is also proposed. Finally, we analyze the implementation of dedicated algorithm to
further attenuate narrow band vibrations. These techniques include a traditional notch filter, whose performance is
compared to a more advanced adaptive vibration cancelation algorithm (AVCA). We find that the AVCA can correctly
reject large amplitude vibrations, even when the AO sampling frequency is low.
Numerical control matrix rotation for the LINC-NIRVANA multiconjugate adaptive optics system
Show abstract
LINC-NIRVANA will realize the interferometric imaging focal station of the Large Binocular Telescope. A double
Layer Oriented multi-conjugate adaptive optics system assists the two arms of the interferometer, supplying
high order wave-front correction. In order to counterbalance the field rotation, mechanical derotation for the
two ground wave-front sensors, and optical derotators for the mid-high layers sensors fix the positions of the
focal planes with respect to the pyramids aboard the wave-front sensors. The derotation introduces pupil images
rotation on the wavefront sensors: the projection of the deformable mirrors on the sensor consequently change.
The proper adjustment of the control matrix will be applied in
real-time through numerical computation of the
new matrix. In this paper we investigate the temporal and computational aspects related to the pupils rotation,
explicitly computing the wave-front errors that may be generated.
Experimental validation of type-II tip-tilt control in a woofer-tweeter adaptive optics system
Show abstract
Woofer-Tweeter Adaptive Optics (AO) systems use two Deformable Mirrors (DM) with a single wavefront
sensor (WFS) to correct for optical aberrations. The splitting of the DM commands derived from the WFS
measurements must accommodate both the spatial and temporal bandwidth of the DMs. This paper reports on
a woofer-tweeter experiment developed at the AO laboratory of the University of Victoria. This experiment uses
a tip-tilt mirror as a woofer and a 9×9 CILAS PZT DM as a tweeter. The response of the woofer is slowed down
in order to reproduce the behavior of the tip-tilt platform supporting the DM of the TMT/ NFIRAOS system.
For this experiment, only the tip-tilt mode is considered, especially the off-loading of the low temporal frequencies
of the tip-tilt mode from the DM to the slow tip-tilt mount is investigated. The closed-loop controller is a type
II controller with a cascade of two integrators and a lead filter. The performance of this Woofer-Tweeter scheme
as measured in the experiment is presented, and compared with the performance predicted by a hybrid Simulink
model. The increased rejection achieved by the type II controller compared to a classical controller is quantified,
as well as the increase in the associated noise propagation.
Real-time open-loop control of a 1024-actuator MEMS deformable mirror
Show abstract
This article reports the progress made at the University of Victoria AO Lab, regarding the realtime
open-loop control of a 1024-actuator MEMS deformable mirror (DM). The setup is an hybrid
woofer-tweeter/open-loop bench. A tip-tilt mirror and a woofer DM (a 57-actuator CILAS DM)
are driven in closed-loop while a 1024-actuator MEMS DM is utilized on a parallel open-loop
path. Previous work shows that open-loop control providing low residual error (with frozen
Kolmogorov turbulence) can be obtained without the need of DM modelling. A preliminary
methodical calibration of the DM is employed instead. The MEMS electronics were upgraded
to an update rate of 500 Hz and the experiment lays the groundwork for showing how these
performances can also be achieved on the bench with dynamic turbulence (created with custom
hot air turbulence generators). The current status of the experiment and the next milestones
are presented.
Recent development in real-time control system of Subaru adaptive optics including laser guide star mode
Show abstract
We report recent development in real time control system of Subaru adaptive optics system. The main topic is
modification of the real time control system for laser guide star operation. The primary change is appending lower order
wave-front sensor. And also, an auxiliary tip-tilt and focus control are appended before higher order waver-front sensor
to absorb the perturbation of the laser beam and height of sodium layer. Our implementations using the control gain
matrix are introduced thoroughly from the basis of the system design and down to the details. Also, other new function
and prospects in the near future will be presented for the cascaded average monitor and the time domain over sampling.
A COTS high-performance real-time control system for adaptive optics
Show abstract
The advent of high performance multi-core processors in desktop computers has opened the door for high
performance, yet easy to maintain and upgrade, adaptive optics control systems. We describe the Durham
Adaptive Optics Real-time Controller, and give details of performance, including latency and jitter, and maximum
frame rates as well as scalability with adaptive optics system size. This system is to be used as a laboratory test
bench in Durham with low and high order (up to 32×32 actuators) systems, and also on-sky as a control system
for a WHT MOAO demonstrator instrument.
SPARTA roadmap and future challenges
Show abstract
SPARTA, the ESO Standard Platform for Adaptive optics Real Time Applications, provides a generic decomposition in
functional blocks that can be applied, unchanged, to a variety of different AO systems, ranging from very small single
conjugate AO with less than 100 actuators to much bigger and faster systems. For AO systems under development,
SPARTA provides an implementation for all those functional blocks that are mapped to currently available technologies.
The E-ELT with its instruments poses new challenges in terms of cost and computational complexity. Simply scaling the
current SPARTA implementation to the size of E-ELT AO system would be unnecessary expensive and in some cases
not even feasible. So, even if the general architecture is still valid, some degree of re-implementation and use of new
technologies will be needed. This paper analyses the new general requirements that the E-ELT and its instruments will
pose and introduces promising technology and solutions that could replace the current ones and show how the SPARTA
architecture could evolve to address those new requirements.
The real-time control system for the CANARY multi-object adaptive optics on-sky demonstrator
Show abstract
CANARY is a Multi-Object Adaptive Optics (MOAO) system designed to demonstrate the AO aspects of proposed EELT
instruments such as the multi-object spectrograph EAGLE. The first phase of Canary will be executed on the 4.2m
William Herschel Telescope in 2010. We describe here the AO Real-time Control System (RTCS) for Canary. This is
based on a distributed architecture of components interconnected by a fast serial fabric (sFPDP). The hardware used is a
hybrid of FPGA and CPU technology. The middleware used for system data telemetry and control is based on CORBA
and the publish/subscribe pattern. The system is designed to be easily modified and extended for the later, higher order,
phases of CANARY. In order to provide the increase in computational power required in higher order systems, the
current CPU technology can be readily replaced by acceleration hardware based on FPGA or GPU technologies. The
Canary RTCS thus provides a test-bed for these new technologies that will be required for E-ELT instruments. These
design concepts can be developed to provide an RTCS for E-ELT instruments and are in line with those under
consideration by ESO for the E-ELT AO systems to which instruments such as EAGLE will be required to interface.
Control system of a dispersed fringe type sensing system of active optics
Show abstract
Active optics plays an important part in segmented mirrors of astronomy telescopes. A dispersed fringe sensor(DFS) using a broadband point source is an efficient method for cophasing and is also highly automated and robust. DFS can estimate the piston between segments only through the spectrum formed by the transmissive
grating's dispersion and therefore can replace the edge sensors. So we build an system in our lab to experiment the DFS method. The whole control system of DFS is put forward, including control of displacement actuators and control of shifting the optical fiber. Control of displacement actuators consists in industry computer,
HY-6120 I/O card, six stepper motor and other parts. Some theoretical analysis and experiment tests reveal that the actuator could be controlled to 5nm and without backlash by this control strategy. The optical fiber could be shifted out of optical path or shifted in part or whole of optical path so that the spectrum formed by the transmissive grating's dispersion could alter. When six actuators are moving, the piston is changing, and the
spectrum is also moving and altering. And the whole control of DFS system is constructed now and seems well.
Further test and experiment will be carry out.
Point-spread function reconstruction for the ground layer adaptive optics system ARGOS
Show abstract
ARGOS is the ground layer adaptive optics system planned for the LBT. Although ground layer adaptive optics
systems provide a relatively homogeneous point spread function over the full field of view there will be still
variations of the order of a few 10%. In the case of a laser based GLAO system these variations are mostly due
to the facts that only one auxiliary guide star is used and to the cone effect. Astrometry and photometry on
AO corrected images are effected by these changes in the shape of the point spread function with field angle.
To reduce this effect for the ARGOS system a scheme for point spread function reconstruction from wavefront
sensor data is developed. The scheme uses the wavefront sensor data twofold: To reconstruct the wavefront
and to measure the atmospheric profile via SLODAR. The reconstruction scheme is tested in simulations of the
full system for various seeing conditions and guide star angles. The quality of the reconstruction is tested in
simulation.
Anisoplanatism across wide fields at high-frame rates
Show abstract
In this paper we present a preliminary analysis of variation in the isoplanatic patch size over short timescales and
wide angular separations. We tested a visible band photon counting camera running with four 1K2 detectors
to provide a contiguous field of view of 1000 × 4000 pixels. Resolution was 35-100 mas per pixel at frame rates
from 20-111hz, providing data on atmospheric turbulence at angular separations of up to 400 arcseconds. We
discuss the potential of such cameras to perform high resolution optical surveys using developments of standard
lucky imaging techniques, and the implications of our results for adaptive optics systems design.
Making a robust, reliable, and a highly available DIMM seeing monitor
Show abstract
During the last 20 years, many DIMM instruments have been developed to measure astronomical seeing. The IAC has
been involved in several projects to run different campaigns to characterize its observatories. However, the cost in
manpower to maintain and operate these instruments has been too high and it is mandatory to minimize this effort by
constructing a reliable, robust and available seeing monitor.
A review of all sources of errors has been done in order to fit very reliable measurements: acquisition parameters, box
size, signal threshold, SNR threshold, flux, deformations and vibrations for centroid calculations, best pixel scale, jitter
in the images sampling, light bandwidth, CCD noise, as well as the centroid calculation algorithm. Experimental
measurements about the influence of exposure time, number of images for computing the seeing or defocus have been
carried out to identify the practical limits of the instrument.
The IAC automatic DIMM design has been reviewed to improve its robustness and its availability to guarantee the
minimum down-time and to maximize the time between failures. The new design will be shown as part of this work.
Atmospheric dispersion correction for the Subaru AO system
Show abstract
In this paper, we present the science path ADC unit (atmospheric dispersion corrector) for the AO188 Adaptive
Optics System of the Subaru Telescope. The AO188 instrument is a curvature-based Adaptive Optics system with
188 subapertures and achieves good correction down to shorter wavelengths like J-band. At these wavelengths, the
atmospheric dispersion within the band becomes significant and thus a correction of the atmospheric dispersion
is essential to reach diffraction-limited image quality. We give an overview of the requirements, the final optical
and mechanical design of the ADC unit, as well as the structure of its control software.
Laser guide star facility at La Silla Paranal Observatory: latest upgrades, operation, and performance
Show abstract
At Paranal Observatory in the YEPUN (UT4) telescope, two instruments are installed and equipped
with adaptive optics systems: an infrared spectro imager (CONICA) below the adaptive optics
module NAOS; and an integral field spectrograph (SINFONI). In the same telescope, the Laser
Guide Star Facility (LGSF) is installed to provide a reference star to the adaptive optics systems. The
LGSF is tuned to the sodium D2 line to use the resonance fluorescence of atomic sodium in the
mesospheric layer at an altitude of 90 Km.
The LGSF system has been fully operational for several years now. During this time, important
modifications have been made to the system to increase its availability, simplify its remote operation
and improve its performance.
In this contribution, we report on the latest upgrades in hardware as well as the software of the
system. Some upgrades like the exchange of the cooling system of the VERDI lasers, as well as the
exchange of motors in the PARSEC laser system, have been critical to improve the performance of
the system. We also describe the improvements in the maintenance and operation procedures and
operational constraints we have faced so far. Finally, we present and analyze the latest technical
performance achieved by the LGSF in operational conditions.
Gemini North Laser Guide Star System: operations and maintenance review
Show abstract
The Gemini North telescope has been providing Laser Guide Star Adaptive Optics (LGS AO) regular science queue
observations for worldwide astronomers since February 2007. In this paper we comment on the reliability of the Laser
Guide Star Facility high-power solid-state laser during normal operations, and discuss progress made on various issues
that will enable a "turn-key" operation mode for the laser system. In this effort to produce consistent, stable and
controlled laser parameters (power, wavelength and beam quality) we completed a failure mode effect analysis of the
laser system and sub systems that initiated a campaign of hardware upgrades and procedural improvements to the routine
maintenance operations. These upgrades are discussed, including pump laser diode replacements, as well as sum
frequency generation (SFG) crystal degradation along with our detailed plans to improve overall laser reliability, and
availability. Finally, we provide an overview of normal operation procedures during LGS runs and present a snapshot of
data accumulated over several years that describes the overall LGS AO observing efficiency at the Gemini North
telescope.
A pulsed guide star laser can be the brightest
Show abstract
We report on a numerical model and supporting experiments to show that a high peak power, pulse
burst, Na guide-star waveform, suitable for use with adaptive optics systems requiring dynamic
refocusing to avoid guide star elongation, is capable of producing a return comparable to
conventional guide star laser of comparable output power. The predictions from our numerical
model using coherent pumping by short, high peak power pulses, or
so-called π-pulse pumping,
indicate that very bright fluorescence returns can be achieved in this regime. This is supported by
experimental results where fluorescence is observed in alkali atoms (cesium) using variable input
power and pulse lengths. The model is used to predict very bright Na guide stars, using short pulses
to excite most of the Na atoms available, followed by sufficient time to let them decay.
Characterizing site specific considerations for protecting aircraft during LGS operations at W. M. Keck Observatory
Show abstract
W. M. Keck Observatory (WMKO) routinely operates laser guide star (LGS) Adaptive Optics (AO) systems at the
telescope facility on the Big Island of Hawaii. One of the operational requirements for the LGS system is that a safety
system to prevent nearby aircraft from being adversely affected by the laser must be provided. We will support
operations in the near term with human aircraft spotters until we can successfully develop and get the appropriate
approvals needed for an Automated, Integrated and Reliable System for an Aircraft Friendly Environment (AIRSAFE).
This report describes some of the preliminary requirements development work at WMKO in support of the future
development of AIRSAFE. We discuss the results of recent work to characterize site specific considerations that impact
requirements development. The site specific considerations include the proximity of WMKO laser operations to nearby
commercial airports, the implications of military operations in the area and the character of the air traffic volume and
flight patterns over the telescope facility. Finally, we discuss how the design and implementation of AIRSAFE will be
impacted by these site specific considerations.
The characteristics of laser-transmission and guide star's brightness for Subaru LGS/AO188 system
Show abstract
We are commissioning the Laser Guide Star Adaptive Optics (LGS/AO188) system for Subaru Telescope at
Hawaii, Mauna Kea. This system utilizes a combination of an
all-solid-state mode-locked sum-frequency generation
(SFG) laser (1.7GHz-bandwidth, 0.7ns-pulse width) as a light source and single-mode optical fiber for beam
transference. However, optical fibers induce nonlinear scattering effects, such as stimulated Raman scattering
(SRS) and stimulated Brillouin scattering (SBS), beyond certain threshold levels in high-power lasers. We measured
the laser transmission characteristics of a photonic crystal fiber (PCF) whose mode field diameter (MFD)
was 11 μ m, and a step index fiber (SIF) cable whose MFD was 4.2 μ m to evaluate the threshold levels for
non-linear effects. We observed SRS in the 200-m-long SIF when we input 1.3W. The material losses of them
were 10db/km and 6.4dB/km, respectively. However, SRS and SBS were not induced in the 200-m-long PCF,
even for an input power of 5.3W. As a result, we estimated the threshold of SRS to be 33W for the 35-m-long
PCF designed for the Subaru LGSAO system.
Other than SRS and SBS, we found self phase modulation (SPM) in our PCF. SPM makes the spectrum
of the laser beam broaden and it causes less efficiency of generating bright LGS. We measured width of the
spectrum by spectrum analyzer. As the result, we found it was 9.1GHz of full width half maximum (FWHM)
in comparison with the original FWHM of our laser spectrum, 2.1GHz. This shows 70% of the laser energy for
brightening the LGS was lost.
We also measured the brightness of the LGS and evaluated its relationship with wavelength of the laser.
The LGS's brightness showed a peculiar tendency that did not be extinguish even though the wavelength has
varied about 2pm. The tendency was not shown with the experiment using sodium gas cell. Therefore, it may
be concerned the environment of the sodium layer in the mesosphere.
Gemini North r' band imaging of the Keck II Laser
Show abstract
The Gemini Multi-Object Spectrograph (GMOS-N), with a field of view of
5.5 × 5.5 arc minutes, was used to obtain r' band images of the
Keck II laser beam. The data samples the Rayleigh scattered laser beam at low
elevations and the sodium spot at the highest elevation. The Rayleigh scattered part of
the beam is large at low elevations, filling the GMOS-N field of view, with high surface
brightness. At higher elevations (85 deg - 89.5 deg) it gets smaller and fainter. We also
present data taken on the laser spot which we see at an elevation of 89.625,
corresponding to a height in the atmosphere of ~100km. In addition, GMOS-N spectra
and GMOS-N on-instrument wavefront sensor (OIWFS) data have been collected that
allow us to characterize the effect that lasers from other telescopes might have on
GMOS-N data. The OIWFS works at wavelengths which include the sodium D band.
The performance of the laser guide star system for the Subaru Telescope
Show abstract
We are developing a laser guide star (LGS) system for the
188-elements Adaptive Optics system (AO188) of the
Subaru telescope. In this paper we describe the results of the performance tests of the LGS system. The beam
that excites sodium atoms at 90 km altitude of the LGS is generated by the following sequence. The source
of the beam is a quasi-CW mode locked sum-frequency generating 589 nm laser. This laser beam propagates
through a diagnostics system for measuring the wavelength and the beam quality. Then it couples into a solidcore
photonic crystal fiber cable for transmitting the beam to a telescope for launching the beam (LLT: Laser
Launching Telescope). The output beam from this fiber cable is collimated by the optics mounted on the
LLT. This collimated beam is expanded by the LLT and launched into the sky. We executed several engineering
observations of the LGS system from 2009 for confirming the performance of all the components in this sequence.
We also report the quality of the LGS.
Optical setup and wavefront sensor for solar adaptive optics at the Domeless Solar Telescope, Hida Observatory
Show abstract
A solar adaptive optics system for a high-dispersion spectrograph is developed at the 60 cm domeless solar telescope of
the Hida Observatory in Japan. Details of its optical setup are described for implementing a scanning slit spectroscopy
with wavefront correction. A wavefront sensor used in the system is specified and a technique of reducing computational
cost in wavefront sensing is also described. In solar observations, the improvement of contrast in images obtained with
the adaptive optics system was demonstrated when a sunspot was used as a target of wavefront sensing.
Symmetrically weighted center of gravity for Shack-Hartmann wavefront sensing on a laser guide star
Show abstract
Phase local gradient measurements in a Shack-Hartmann (SH) wavefront sensor (WFS) are achieved by tracking
the displacements of a spot in each sub-aperture. This can be done by comparing the position of its center-ofgravity
(COG) to a reference position. A commonly used method for position tracking is the weighted (W) COG
in which the original image is multiplied by a weighting function, before centroiding. However, it can be shown
that, if the spot centered on its COG is not even, the WCOG estimator is biased. We propose a new method
for spot centroiding with a direct application to wavefront sensing on a LGS: the symmetrically weighted (SW)
COG, in which the weighting function is taken as the symmetrical version of the spot, with respect to its COG.
Pyramid wavefront sensing with a laser guide star for an ELT
Show abstract
The wavefront sensor [WFS] is a key element of an Adaptive Optics [AO] system. It gives access to a direct
measurement of the turbulent phase, its curvature or its slope, from which the mirror voltages are computed. The
ability of the system to correct efficiently the atmospheric turbulence is strongly dependent on the performance
of the WFS in estimating the turbulent phase. The Shack-Hartmann [SH] WFS has been for a long time the
standard used in AO systems. In 1996, it has been proposed1 a new generation WFS, the pyramid WFS. It is a
focal plane WFS, based on the principle of a Foucault knife-edge. It has been demonstrated that it provides a
consistent gain with respect to the Shack-Hartmann.2,5-7 More recently, improvements were proposed to increase
the pyramid performance.3, 4 On the framework of the developpement of extremely large telescopes, the interest
of a pyramid wave front sensor appears clearly. But its behaviour with laser guide stars [LGS], most probably
necessary in any Extremely Large Telescope [ELT], is still relatively unknown. Some WFS dedicated to LGS
wave front sensing has already been proposed8,9 but a full study of the pyramid WFS behaviour is still necessary.
This work's aim is to bring answers to this topic.
Error propagation in curvature sensors
Show abstract
The effect of measurement noise on the phase reconstruction is here analyzed for curvature sensors. It is shown,
that for a fixed extra-focal distance the phase variance depends only on the number of photons and is independent
of the number of sensing elements.
The error propagation factor is further computed for three different sampling geometries: square and hexagonal
grids and the polar geometry commonly used for curvature sensors. The error propagation factor is seen to
be almost independent of the grid geometry.
Wavefront sensors and algorithms for adaptive optical systems
Show abstract
The results of recent works related to techniques and algorithms for wave-front (WF) measurement using
Shack-Hartmann sensors show their high efficiency in solution of very different problems of applied optics. The goal of this
paper was to develop a sensitive Shack-Hartmann sensor with high precision WF measurement capability on the base of
modern technology of optical elements making and new efficient methods and computational algorithms of WF
reconstruction. The Shack-Hartmann sensors sensitive to small WF aberrations are used for adaptive optical systems,
compensating the wave distortions caused by atmospheric turbulence. A high precision Shack-Hartmann WF sensor has
been developed on the basis of a low-aperture off-axis diffraction lens array. The device is capable of measuring WF
slopes at array sub-apertures of size 640×640 μm with an error not exceeding 4.80 arcsec (0.15 pixel), which corresponds
to the standard deviation equal to 0.017λ at the reconstructed WF with wavelength λ . Also the modification of this
sensor for adaptive system of solar telescope using extended scenes as tracking objects, such as sunspot, pores, solar
granulation and limb, is presented. The software package developed for the proposed WF sensors includes three
algorithms of local WF slopes estimation (modified centroids, normalized cross-correlation and fast Fourierdemodulation),
as well as three methods of WF reconstruction (modal Zernike polynomials expansion, deformable
mirror response functions expansion and phase unwrapping), that can be selected during operation with accordance to the
application.
The laser guide stars wavefront sensor prototype for the E-ELT: test results
Show abstract
The current baseline for the Multi-Conjugate adaptive optics module (MAORY) for the European Extremely Large
Telescope is based on the Sodium Laser Guide Stars (LGS) approach, in order to ensure correction uniformity and sky
coverage. However, since the Sodium layer is approximately 10 km thick, the artificial reference source looks elongated,
especially when observed from the edge of a large aperture, with elongation depending on the actual telescope diameter,
on the Sodium layer properties and on the laser launcher position. We studied numerically, by means of simulations, the
performance of three different algorithms for the instantaneous LGS image position measurement in presence of
elongated spots: the Weighted Center of Gravity, the Correlation and the Quad-cell. Since all the three considered
algorithms require some sort of 'reference', the problem of the temporal variation of the Sodium Layer properties has to
be addressed. Another important aspect that has be addressed in the analysis is the impact of the low-order aberrations
introduced by the MAORY re-imaging optics, by the Sodium Density profile shape and by its projection in the LGS
image plane. An LGS wavefront sensor laboratory prototype was designed to reproduce the relevant aspects of a
Shack-Hartmann wavefront Sensor for the European Extremely Large Telescope and, through laboratory tests, to evaluate the
performance of different centroid algorithms in presence of elongated spots, with realistic Sodium profiles, as previously
investigated numerically and analytically, analyzing the impact of the low-order aberrations and of relevant WFS
parameters, like signal-to-noise ratio, sampling and subaperture size. This paper shows the results of the tests performed
with this prototype.
Wide-field AO correction: the large wavefront sensor detector of ARGOS
Show abstract
Wide field correction allowing large field to benefit from adaptive optics (AO) is challenging in more than one
aspect. We address here the wavefront sensor (WFS) detector side where, in addition to high sensitivity and low
noise, the simultaneous detection of multiple laser beacons and the large number of sub-apertures in a
Shack-Hartmann WFS require a detector to have a large imaging area while preserving a very high readout frame
rate. The detector considered has a frame area of 264×264 pixels with a pixel size of 48 microns. By splitting
the image into two framestore areas during readout, repetition rates of more than 1000 frames per second can
be achieved. The electronic noise contribution is approximately 3 electrons at the operating temperature. We
therefore analyze its performances, showing it fulfills the requirements, in a wavefront sensing application: the
measurement of centroids in the case of a Shack-Hartmann WFS for the Argos AO project.
The Gemini Planet Imager calibration wavefront sensor instrument
Show abstract
The Gemini Planet Imager is an extreme adaptive optics system that will employ an apodized-pupil coronagraph to make
direct detections of faint companions of nearby stars to a contrast level of the 10-7 within a few lambda/D of the parent
star. Such high contrasts from the ground require exquisite wavefront sensing and control both for the AO system as well
as for the coronagraph. Un-sensed non-common path phase and amplitude errors after the wavefront sensor dichroic but
before the coronagraph would lead to speckles which would ultimately limit the contrast. The calibration wavefront
system for GPI will measure the complex wavefront at the system pupil before the apodizer and provide slow phase
corrections to the AO system to mitigate errors that would cause a loss in contrast. The calibration wavefront sensor
instrument for GPI has been built. We will describe the instrument and its performance.
Prototype of a laser guide stars wavefront sensor for E-ELT: design and integration
Show abstract
In the framework of the studies related to the European Extremely Large Telescope (E-ELT), a fundamental importance
must be given to Sodium Laser Guide Stars (LGS) Wavefront Sensing which is essential to permit wide correction
uniformity and a relevant sky coverage. The finite distance of the sodium layer where the LGSs form, its width and
density time variability, requires detailed studies in order to better perform the wavefront measurement. Many LGS
peculiar problems, such as perspective elongation, focus uncertainty and launching angle , that can be neglected or more
easily managed for 8m class telescopes, become fundamental issues in the design of future LGS Wave-Front Sensors
(WFSs) for the E-ELT. In this paper we present the LGS WFS prototype built at the Osservatorio Astronomico di
Bologna reproducing the expected conditions of a E-ELT like LGS Shack-Hartmann WFS. The main scope of the
prototype is to cross check the simulations concerning the centroiding algorithms in the case of elongated spots using
different light intensities, pixel scales, spot offsets, sub-aperture Field of Views and elongated source intensity profiles.
Starting from the conceptual idea we show the system design and the integration in the lab. Finally the prototype optical
quality and its capability to perform the required tests are presented.
Performance of a Shack-Hartmann wavefront sensor using real sodium laser data
Show abstract
The future of adaptive optics includes laser guide stars. While they are a great solution to sky coverage, they
do introduce additional errors in the adaptive optics system. In particular, because of the finite thickness of
the sodium layer, there is reduced centroiding accuracy due to elongated spots in the wavefront sensor. These
become even more pronounced on large telescope apertures. In this paper we focus on the performance of a
Shack-Hartmann wavefront sensor for 30m-plus large aperture telescopes studying the consequences of both the
decrease in signal to noise ratio due to the spot elongation and the variations of the sodium density variations in
the mesosphere. We incorporate real on-sky measurements of the return from the sodium layer using images of
the laser guide star taken at Lick Observatory and simulate the expected wavefront reconstruction performance
in the case of a Thirty Meter Telescope. Using this ensemble of data, we compare performance for various
Hartmann centroiding methods, including correlation and weighted least square algorithms.
Characterization of synthetic reconstructors for the pyramid wavefront sensor unit of LBTI
Show abstract
We present progress and results for the pyramid wavefront sensor unit on the Large Binocular Telescope's
Interferometer (LBTI). The system is a clone of the pyramid sensor unit developed at Arcetri Observatory for
the LUCIFER instrument. We discuss the performance of simulated reconstructors during preliminary on-sky
testing at the MMT. These reconstructors were generated with the code AOSim2, a customizable end-to-end
simulator of a telescope and its AO system. We used the 3-5μm imager Clio to take fast exposures at 3.8μm, from
which we calculated Strehl Ratios (SR) for each pyramid configuration and for the Shack-Hartmann (SH) system
currently installed. We obtained instantaneous SR as high as 60% for the pyramid as compared to 65% mean for
the SH.We identify improvements which will increase the SR in future implementations. These tests demonstrate
the feasibility of commissioning a pyramid wavefront sensor on LBTI using a synthetic reconstructor.
Visible low-order wavefront sensor for the Subaru LGSAO system
Show abstract
The Subaru laser guide star adaptive optics system (AO188) was installed at the Nasmyth focus of the Subaru
Telescope on October 2006 and it is in operation with the natural guide star (NGS) mode. The operation of
the laser guide star (LGS) mode started on January 2010. A visible low-order wavefront sensor (LOWFS) was
built to measure tip-tilt and defocus terms of wavefront by using a single NGS within a 2.7 arcmin diameter field
when an LGS is used for high-order wavefront sensing with the 188-element curvature based wavefront sensor.
This LOWFS is a 2 × 2 sub-aperture Shack-Hartmann sensor with 16 photon-counting avalanche photodiode
(APD) modules. A 4×4-element lenslet array is located after the 2 × 2 sub-aperture Shack-Hartmann lenslet
array and it is coupled with the APD modules through optical fibers. The field of view of the LOWFS is 4 arcsec
in diameter. It has own guide star acquisition unit, acquisition and pupil cameras, and atmospheric dispersion
corrector. We describe the design, construction, and integration of this low-order wavefront sensor.
Handling complex adaptive optics concepts including the third and fourth dimensions
Show abstract
Adaptive Optics (AO) concepts involve sometimes very complex behaviors of rays, waves and optical elements. Just
think, to be convinced, the way multiple probes aim to correct for a large field of view Multi Conjugated AO, and to how
these deploy onto a dynamic turbulent atmosphere. In order to explain the behavior of novel concepts we developed
visualization techniques that involve the display of three dimensional images and the creation of movies to explain how
the concept deals with an evolving situation, or, in other words, adding the fourth dimension of time. We produce solid
models of the optical concepts we are developing, including the evolving temporal behavior of the turbulence, and these
can be manipulated in a virtual manner in order to allow for the production of different means of visualization. These
ranges from so called "static movies" where a three dimensional concept is just explored in three dimension by handling
it around the observer, to the creation of three dimensional anaglyphs or anaglyphs movies. While the paper is mainly
focused onto the ways these techniques are exploited in order to produce satisfactory results, the poster allow the visitor
to experience some of these images and movies. The aim of this work is not only of a sort of high level didactical
purpose, but we think it would be useful into scientific discussion and during meeting to develop engineering concepts of
several AO concepts.
Integration and alignment of adaptive optics systems: 10 years of experience at the VLT
Sébastien Tordo
Show abstract
The number and importance of the adaptive optics instruments has grown in the world through the last two decades.
Such systems are becoming key elements for large telescopes, with increasing types and complexity. The Very Large
Telescope (VLT) has been equipped with many instruments using adaptive optics such as Shack-Hartmann, curvature or
pyramid wavefront sensors. In this framework the European Southern Observatory (ESO) has collected a large expertise
in the field of instrument integration and in particular the integration of adaptive optics systems. The purpose of this
article is to share this expertise with the community and tell how instruments are being built in our organization.
Therefore this article is aimed at persons who have some or little experience in integration and optical alignment.
Final design of the wavefront sensor unit for ARGOS, the LBT's LGS facility
Show abstract
In this paper we present the final design of the WFS unit of LBT's ARGOS facility, that will implement a GLAO system
using 3 Rayleigh pulsed beacons. The ARGOS WFS is composed of two main subunits: 1) a large dichroic
window that deflects the laser beam toward the WFS and transmit the visible and near-infrared wavelength to the MOSimager
LUCIFER and 2) the SH-WFS that collects the backscattered light of the 3 beacons and combines the beams on
a single lenslet array and detector. The WFS unit includes Pockels cells for the range gating of the laser beams, field and
pupil stabilizers to compensate for the fast jitter of the laser beams and for optical flexures and a calibration unit to check
the internal alignment; this unit will be also used for closed-loop laboratory tests using a MEMS-DM.
Laboratory test of application of electric field conjugation image-sharpening to ground-based adaptive optics
Show abstract
High contrast imaging is an ongoing theme in the domain of astronomy, both for ground-based and space-based
telescopes. Achieving 106 - 107 contrasts expected with GPI and SPHERE or 1010 contrast for space projects,
requires extreme wavefront correction as well as good coronagraphic systems. With the testbed located at the
Laboratory of Adaptive Optics in Santa Cruz, we statically correct the wavefront to 0.5 nm in band and reach
contrast of a few 107 with an Apodized Lyot Coronagraph (APLC). The Electric Field Conjugation (EFC) allows
us to further improve on this performance. EFC is a formalism of the correction problem that computes the
actuator commands for the deformable mirror (DM) to correct for both amplitude and phase in a pre-defined
region in the final image plane. In order to take into account
non-common-path errors and potential amplitude
aberrations, the proper actuator commands are computed using an image plane-based DM diversity by means of
reconstructing the complex electric field. Already successfully tested for space-based telescopes, we here attempt
to adapt this method to ground-based observations, using the EFC high contrast solution to record new reference
centroids for a Shack-Hartmann wavefront sensor, which in turn can be used to recreate the far-field image. This
paper shows results of this first use of the EFC method with an APLC. We achieved 4.108 contrast on a [4-9]
λ/d square region. We also show that it can be applied to ground based adaptive optics, using Shack-Hartmann
wavefront sensors.
Integrated dual-stage deformable mirrors
Show abstract
We present the results of a study on Dual-Stage Deformable Mirrors using Zonal Bimorph Deformable Mirror (ZBDM)
technology. A high density 'tweeter' DM has been assembled onto a lower density, high dynamic range 'woofer' DM to
generate an integrated mirror which offers both high resolution and dynamic range simultaneously. Such a device has the
potential to significantly simplify the design of astronomical Adaptive Optics (AO) systems. The latest developments are
presented, including the fabrication of a small scale demonstrator.
Progress in developing a low-cost deformable mirror
Show abstract
Large (>1m) deformable mirrors with hundreds or thousands of actuators are attractive for extremely large
telescopes. Use of force actuators coupled to the mirror via suction cups, and electret microphones for position
sensing, has the potential of substantially reducing costs. However, a mirror controlled with force actuators
will have many structural resonances within the desired system bandwidth, shifting the emphasis somewhat
of the control aspects. Local velocity and position loop for each actuator can add significant damping, but
gives poor performance at high spatial frequencies. We therefore introduce a novel control strategy with many
parallel "actuator families", each controlled by
single-input-single-output controllers. This family approach
provides performance close to that of global control, but without the accompanying robustness challenges. Using
a complete simulation model of a representative large deformable mirror, we demonstrate feasibility of the
approach.
This paper describes the challenges of non-ideal actuators and sensors. The results presented give an understanding
of the required actuator bandwidth and the effects of the sensors dynamics. The conclusion is that the
introduction of actuator and sensor dynamics does not limit the control system of the deformable mirror.
High-power visible laser effect on a Boston Micromachines' MEMS deformable mirror
Show abstract
Continuous-facesheet and segmented Boston Micromachines Corporations' (BMC) Micro-Electrical Mechanical Systems (MEMS) Deformable Mirrors (DM) have been tested for their response to high-power visible-wavelength laser light. The deformable mirrors, coated with either protected silver or bare aluminum, were subjected to a maximum of 2 Watt laser-light at a wavelength of 532 nanometers. The laser light was incident on a ~ 3.5×3.5 cm area for time periods from minutes to 7 continuous hours. Spot heating from the laser-light is measured to induce a local bulge in the surface of each DM. For the aluminum-coated continuous facesheet DM, the induced spot heating changes the surface figure by 16 nm rms. The silver-coated
continuous-facesheet and segmented (spatial light modulator) DMs experience a 6 and 8 nm surface rms change in surface quality with the laser at 2 Watts. For spatial frequencies less than the actuator spacing (300 mm), the laser induced surface bulge is shown to be removable, as the DMs continued to be fully functional during and after their exposure. Over the full 10 mm aperture one could expect the same results with a 15 Watt laser guide star (LGS). These results are very promising for use of the MEMS DM to pre-correct the outgoing laser light in the Laboratory for Adaptive Optics' (LAO) laser uplink application.
Demonstration prototype and breadboards of the piezo stack M4 adaptive unit of the E-ELT
Show abstract
In order to mitigate the risks of development of the M4 adaptive mirror for the E-ELT, CILAS has proposed to build a
demonstration prototype and breadboards dedicated to this project. The objectives of the demonstration prototype
concern the manufacturing issues such as mass assembly, integration, control and polishing but also the check the global
dynamical and thermal behaviour of the mirror. The local behaviour of the mirror (polishing quality, influence function,
print through...) is studied through a breadboard that can be considered as a piece of the final mirror. We propose in this
paper to present our breadboard strategy, to define and present our mock-up and to comment the main results and lessons
learned.
Imaging polarimetry with the Gemini Planet Imager
Show abstract
The Gemini Planet Imager (GPI), currently under construction for the 8-m Gemini South telescope, is a high contrast adaptive
optics instrument intended for direct imaging of extrasolar planets and circumstellar disks. GPI will study circumstellar
disks using the polarization of disk-scattered starlight. These observations will be obtained using a novel 'integral field
polarimetry' mode, in which the dispersing prism of GPI's integral field spectrograph is replaced by a Wollaston prism,
providing simultaneous dual polarimetry for each position in the field of view. By splitting polarizations only after the instrument's
lenslet array, this design minimizes wavefront differences between the polarization channels, providing optimal
contrast for circumstellar dust. A rotating achromatic waveplate provides modulation. End-to-end numerical modeling
indicates that GPI will be sensitive to scattered light from debris disks significantly fainter than can currently be imaged.
We discuss the tradeoffs and design decisions for GPI polarimetry, describe the calibration and reduction procedures, and
present the current status of the instrument. First light is planned for 2011.
Focal plane wavefront sensor sensitivity for ELT planet finder
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In the framework of Extremely Large Telescope (ELT), several instruments are considered for the characterization of
extrasolar planets. Since the performance of such an instrument is limited by wavefront errors, the use of extreme
Adaptive Optic (AO) systems is mandatory. Studies for future planet finder instruments such as SPHERE/VLT or
GPI/GEMINI show that one limitation of the performance for a planet finder is the differential aberrations that are not
measured by the wavefront sensor, which is physically separated from the common optics by a beam splitter. These
defects create a field of residual speckles in the focal plane that need to be calibrated to separate the planet signal from
the speckle noise [1].
We propose here to simultaneously estimate these aberrations and also detect the planet directly from the final science
image. To do so, we propose to couple the foreseen extreme high speed AO of an ELT planet Finder with a low speed
Self-Coherent Camera (SCC [2-5]). The SCC which is based on the principle of light coherence can both estimate the
wavefront errors and reduce speckle noise by calibration. After recalling the principle of the SCC, we present simulation
results of the SCC performance in the context of EPICS.
Application of wavelength diversity for astronomical adaptive optics imaging
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Wavelength diversity uses multi-wavelength data to simultaneously estimate the point spread function (PSF)
of an imaging system and the astronomical object of interest e.g. a binary star with a faint companion. The
algorithm presented does not recover the PSFs directly but estimates the Zernike coefficients of the residual
wavefront phase aberration in the pupil of the telescope. For dual, and triple, channel point source imaging, the
common wavefront is estimated and the residuals between the measured and estimated PSFs correspond to non
common path aberrations in each of the imaging paths.
The Subaru coronagraphic extreme AO (SCExAO) system: visible imaging mode
Show abstract
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system is an instrument designed to be inserted
between the Subaru AO188 system and the infrared HiCIAO camera in order to greatly improve the contrast
in the very close (less than 0.5") neighbourhood of stars. Next to the infrared coronagraphic path, a visible
scientific path, based on a EMCCD camera, has been implemented. Benefiting from both Adaptive Optics (AO)
correction and new data processing techniques, it is a powerful tool for high angular resolution imaging and
opens numerous new science opportunities. We propose here a new image processing algorithm, based on the
selection of the best signal for each spatial frequency. A factor 2 to 3 in Strehl ratio is obtained compared to
the AO long exposure time depending on the image processing algorithm used and the seeing conditions. The
system is able to deliver diffraction limited images at 650 nm (17 mas FWHM).We also demonstrate that this
approach offers significantly better results than the classical select, shift and add approach (lucky imaging).
Weighing black holes using open-loop focus corrections for LGS-AO observations of galaxy nuclei at Gemini Observatory
Show abstract
We present observations of early-type galaxies with laser guide star adaptive optics (LGS AO) obtained at Gemini North
telescope using the NIFS integral field unit (IFU). We employ an innovative technique where the focus compensation
due to the changing distance to the sodium layer is made 'open loop', allowing the extended galaxy nucleus to be used
only for tip-tilt correction. The purpose of these observations is to determine high spatial resolution stellar kinematics
within the nuclei of these galaxies to determine the masses of the super-massive black holes. The resulting data have
spatial resolution of 0.2" FWHM or better. This is sufficient to positively constrain the presence of the central black hole
in even low-mass early-type galaxies, suggesting that larger samples of such objects could be observed with this
technique in the future. The open-loop focus correction technique is a supported queue-observing mode at Gemini,
significantly extending the sky coverage in particular for faint, extended guide sources. We also provide preliminary
results from tests combining tip/tilt correction from the Gemini peripheral guider with on-axis LGS. The current test
system demonstrates feasibility of this mode, providing about a factor 2-3 improvement over natural seeing. With
planned upgrades to the peripheral wave-front sensor, we hope to provide close to 100% sky coverage with low Strehl
corrections, or 'improved seeing', significantly increasing flux concentration for deep field and extended object studies.
Demonstration of on sky contrast improvement using the modified Gerchberg-Saxton algorithm at the Palomar Observatory
Show abstract
We have successfully demonstrated significant improvements in the high contrast detection limit of the Well-Corrected
Subaperture (WCS) using a number of steps aimed at reducing non-common path (NCP) wavefront errors, including the
Autonomous Phase Retrieval Calibration (APRC)1 software package developed at the Jet Propulsion Laboratory (JPL)
for the Palomar adaptive optics instrument (PALAO). APRC utilizes the Modified Gerchberg-Saxton (MGS) wavefront
sensing algorithm, also developed at JPL2. The WCS delivers such excellent correction of the atmosphere that NCP
wavefront errors not sensed by PALAO but present at the coronagraphic image plane begin to factor heavily as a limit to
contrast. The APRC program was implemented to reduce these NCP wavefront errors from 110 nm to 35 nm (rms) in
the lab, and now these exceptional results have been extended to targets on the sky for the first time, leading to a
significant suppression of speckle noise. Consequently we now report a contrast level of very nearly 1×10-4 at
separations of 2λ/D before the data is post processed, and 1×10-5 after post processing. We describe here the major
components of our instrument, the work done to improve the NCP wavefront errors, and the ensuing excellent on sky
results, including the detection of the three exoplanets orbiting the star HR8799.
Frame selection techniques for the Magellan adaptive optics VisAO camera
Show abstract
The Magellan AO system will begin commissioning in early 2012. Its VisAO camera will provide 20 mas
FWHM images with mean Strehl ratios of ~ 0.2 in R band on a 6.5m telescope. Depending on seeing conditions,
Strehl ratio may reach temporary peaks as high as 0.5 at these wavelengths. To take advantage of these brief
periods of high performance, we plan to adopt lucky imaging style data taking and reduction techniques. As part
of this effort we have developed a novel real-time frame selection technique, which will use AO system telemetry
and a fast shutter to limit CCD exposure to these very brief moments of higher Strehl. Here we describe the
expected benefits of our frame selection techniques in various operating modes. We also present the results of
laboratory characterization of the shutter, and describe the performance of predictive algorithms used to control
it.
Novel technologies for small deformable mirrors
Show abstract
Adaptive optic requirements for instrumentation such as EAGLE for the European extremely large telescope present an
enormous challenge to deformable mirror technology. We have developed a unique approach using fabricated arrays of
multilayer actuator technology to address the requirements of actuator density and deflection. Our programme of work
has uncovered a novel approach which has led to a built in test capability. We will present the outcomes of our work
which we believe will lead to a compact deformable mirror.
The LSST camera corner raft conceptual design: a front-end for guiding and wavefront sensing
Show abstract
The Large Synoptic Survey Telescope (LSST) is a proposed ground based telescope that will perform a comprehensive
astronomical survey by imaging the entire visible sky in a continuous series of short exposures. Four special purpose
rafts, mounted at the corners of the LSST science camera, contain wavefront sensors and guide sensors. Wavefront
measurements are accomplished using curvature sensing, in which the spatial intensity distribution of stars is measured
at equal distances on either side of focus by CCD detectors. The four Corner Rafts also each hold two guide sensors. The
guide sensors monitor the locations of bright stars to provide feedback that controls and maintains the tracking of the
telescope during an exposure. The baseline sensor for the guider is a Hybrid Visible Silicon hybrid-CMOS detector. We
present here a conceptual mechanical and electrical design for the LSST Corner Rafts that meets the requirements
imposed by the camera structure, and the precision of both the wavefront reconstruction and the tracking. We find that a
single design can accommodate two guide sensors and one split-plane wavefront sensor integrated into the four corner
locations in the camera.
New techniques for the live update of gain tables in NGS and LGS WFS operation
Show abstract
The gain in Hartmann sensors varies if the shape of the guide star varies. For Natural Guide Star (NGS) operation, this
can be an extended object which changes, e.g. a Comet. For a Sodium Laser Guide Star (LGS) system the spots change
if the Sodium Layer changes or r0 changes. New techniques are presented for estimating and correcting gain tables in
real time AO closed loop operation. One involves looking for reference in the null space (i.e. slope discrepancy space) of
the reconstruction matrix, and the other involves a new WFS output, the cross difference. These techniques are applied
to NGS and LGS operation.
Novel technologies for large deformable mirrors
Show abstract
We have been developing a series of novel technological solutions to address the challenges posed by the adaptive optic
requirements for extremely large telescopes. Our deformable mirror surface material, a compliant from of silicon
carbide, offers a Young's Modulus comparable to glass but with greater, non-catastrophic, resistance to fracture. In
combination with the extraordinary new material we have been working on a new low power actuator with a deflection
capability of tens of microns. We have considered the systems requirements for our deformable mirror and developed
both a coating technology and a unique use of hydroxide catalysis bonding.