The performance of an Adaptive Optics (AO) System relies on the accuracy of its Interaction Matrix which defines the opto-geometrical link between the Deformable Mirror (DM) and the Wave Front Sensor (WFS). Any mis-registrations (relative shifts, rotation, magnification or higher order pupil distortion) will strongly impact the performance, especially for high orders AO systems. Adaptive Telescopes provide a constraining environment for the AO calibration with large number of actuators DM, located inside the telescope with often no access to a calibration source and with a high accuracy required. The future Extremely Large Telescope (ELT) will take these constraints to another level with a longer calibration time required, no artificial calibration source and most of all, frequent updates of the calibration during the operation. To overcome these constraints, new calibration strategies have to be developed either doing it on-sky or working with synthetic models. The most promising approach seems to be the Pseudo-Synthetic Calibration. The principle is to generate the Interaction Matrix of the system in simulator, injecting the correct model alignment parameters identified from on-sky Measurements. It is currently the baseline for the Adaptive Optics Facility (AOF) at the Very Large Telescope (VLT) working with a Shack-Hartmann WFS but it remains to be investigated in the case of the Pyramid WFS.
The long commissioning of the Adaptive Optics Facility (AOF) project has been completed shortly after this conference, providing AO correction to two Very Large Telescope (VLT) foci supported by an adaptive secondary mirror and four laser guide stars. Four AO modes are delivered: a Single Conjugate AO (SCAO) system for commissioning purpose, wide field and medium field Ground Layer AO (GLAO) for seeing improvement and narrow field Laser Tomography AO (LTAO) for ultimate performance. This paper intends to describe the implemented AO baseline and to highlight the most relevant results and lessons learned. In particular, it will address the control and reconstruction strategy, the wavefront sensing baseline and the online telemetry used to optimize the system online, estimate the turbulence profile and calibrate the misregistrations. Focusing on the LTAO mode, we will describe the tomography optimization, by exploring the reconstruction parameter space. Finally, on sky performance results will be presented both in terms of strehl ratio and limiting magnitude.
The ESO’s adaptive optics facility (AOF) is ending its commissioning at Paranal (Chile). It feeds two second-generation instruments of the VLT-UT4 telescope, HAWK-I and MUSE, with turbulence corrected wavefronts through the GALACSI and GRAAL modules. The main features of the AOF are its deformable secondary mirror with 1170 actuators and a laser asterism of 4 artificial stars that probe the atmosphere via four high-resolution Shack-Hartmann wavefront sensors (WFS), each with 40x40 subapertures. The system provides ground layer adaptive optics (GLAO) and laser tomography adaptive optics (LTAO) capabilities. In order to support the commissioning phases of the project, and later optimize and diagnose the operation of the system, a turbulence profiler has been developed and installed in SPARTA, the AOF real time controller (RTC). The profiler estimates two key turbulence parameters: the Cn2(h) and the outer scale (L0(h)) profiles and no limit on the number of the estimated layers exists, but for eight layers, the method takes about 2 minutes to yield a full characterization of the atmosphere. The maximum line of sight distance that the profiler can probed the atmosphere depends on the star separation defined for each operation mode: 3km for GRAAL; 14 km for GALACSI wide field and over 35km for GALACS narrow field mode. The remaining turbulence above these maxima (unseen turbulence from the undetected layers) are essential in the GRAAL mode and it is reliably estimated thanks to a novel method to determine the noise in the WFSs, which is mandatory for estimating this upper segment of the turbulence. The technique is also useful to alert about operational problems such as dome seeing and mis-registrations. The method is currently installed in the SPARTA RTC, providing continuous online estimations for the GALACSI (narrow and wide field modes), and for GRAAL mode. Results for several nights comprising hundreds of profiles show very good agreement with other independent measurements.
The Adaptive Optics Facility (AOF) is an ESO project, which transformed Yepun, one of the four 8m telescopes in Paranal, into an adaptive telescope. This has been done by replacing the conventional secondary mirror of Yepun by a Deformable Secondary Mirror (DSM) and attaching four Laser Guide Stars (LGS) Units to its centerpiece. Additionally, two Adaptive Optics (AO) modules (GALACSI serving MUSE a 3D spectrograph, and GRAAL, serving Hawk I a wide field infrared imager) have been assembled onto the telescope Nasmyth adapters, each of them incorporating four LGS WaveFront Sensors (WFS) and one tip-tilt sensor used to control the DSM at 1 kHz frame rate. The complete AOF is installed on Yepun for more than one year now, and its commissioning is fully complete. This paper presents the most important and amazing features of the AOF, illustrated by some first science images obtained using MUSE/GALACSI in Ground Layer AO (GLAO) and Laser Tomography AO (LTAO) mode, and HAWK-I/GRAAL in GLAO mode. In the first part of the paper, on-sky performance of GRAAL and GALACSI is presented in terms of gain in image quality and even Strehl Ratio. Efficiency of the on-sky operation of the AOF is described. In the second part, future instruments making use of the AOF capabilities are presented.
The construction of a diffraction limitable telescope as large as the ESO’s ELT is enabled by its embedded deformable quaternary mirror. Besides its essential function in the telescope control, M4 also contributes to compensating the free atmosphere aberrations for all post-focal AO applications. The paper presents how the telescope manages M4 to maintain its optical performance while offering to the instruments a clean wavefront interface, supporting the desired AO functionalities. The paper reviews the telescope strategy to derive its wavefront dynamic properties directly from the analysis of the control data collected in science mode, with the goal to minimize the observatory time spent on dedicated wavefront calibration tasks.
The Adaptive Optics Facility (AOF) is one of the most important ESO projects developed for the VLT programme in the last years. The AOF, currently still under commissioning, brings built-in AO capabilities (GLAO and LTAO) to one of the VLT 8m Telescopes (Yepun) that is now equipped with a deformable secondary mirror (DSM), four lasers guide stars (4LGSF) and two AO modules: GRAAL for the HAWK-I infrared imager and GALACSI for the MUSE 3D spectrograph. This paper describes the main aspects of the software responsible for the control and monitor of the two AO modules, as well as for the coordination of subsystems like the instruments and the telescope. Furthermore details of the strategy followed to minimize the impact on configuration control associated to several commissioning periods interleaved with normal operations will be given. The control software package consist of a set of modules based on the VLT Instrumentation Framework and on the VLT platform for AO Real-Time Applications (SPARTA). We will present the software and control design choices that have contributed to the successful commissioning and science verification of GALACSI Wide Field Mode (WFM) and the first verifications of GRAAL tip/tilt free mode covering the control of challenging devices such as the GRAAL Corotator or the GALACSI visible Field Selector together with the innovative and flexible implementation of the AO acquisition sequence and its seamless integration to the instrument observations, the handling of secondary loops and the development of health-check and commissioning scripts (templates) that automated the verification of the different observing modes.
The High Acuity Wide field K-band Imager (HAWK-I) instrument is a cryogenic wide field imager operating in the wavelength range 0.9 to 2.5 microns. It has been in operations since 2007 on the UT4 at the Very Large Telescope Observatory in seeing-limited mode. In 2017-2018, GRound Layer Adaptive optics Assisted by Lasers module (GRAAL) will be in operation and the system GRAAL+HAWK-I will be commissioned. It will allow: deeper exposures for nearly point-source objects, or shorter exposure times for reaching the same magnitude, and/or deeper detection limiting magnitude. With GRAAL, HAWK-I will operate more than 80% of the time with an equivalent K-band seeing of 0.55" (instead of 0.7" without GRAAL). GRAAL is already installed and the operations without adaptive optics were commissioned in 2015. We discuss here the latest updates on performance from HAWK-I without Adaptive Optics (AO) and the preparation for the commissioning of the system GRAAL+HAWK-I.
GRAAL is the adaptive optics module feeding the wide-field IR imager HAWK-I at the VLT observatory. As part of the adaptive optics facility, GRAAL is equipped with 4 Laser-guide star wave-front sensors and provides a large field-of-view, ground layer correction system to HAWK-I. After a successful testing in Europe, the module has been re-assembled in Chile and installed at the Nasmyth-A platform of Yepun, the fourth Unit telescope of the observatory. We report on the installation of GRAAL on the mountain and on its first testing in stand-alone and on-sky.
We present the latest comparison results between laboratory tests carried out on the ASSIST test bench and Octopus end-to end simulations. We simulated, as closely to the lab conditions as possible, the different AOF modes (Maintenance and commissioning mode (SCAO), GRAAL (GLAO in the near IR), Galacsi Wide Field mode (GLAO in the visible) and Galacsi narrow field mode (LTAO in the visible)). We then compared the simulation results to the ones obtained on the lab bench. Several aspects were investigated, like number of corrected modes, turbulence wind speeds, LGS photon flux etc. The agreement between simulations and lab is remarkably good for all investigated parameters, giving great confidence in both simulation tool and performance of the AO system in the lab.
The use of smaller subapertures on some recent adaptive optics (AO) systems seems to yield difficulties in wavefront reconstruction, known as spider effect or pupil fragmentation: the size of the subapertures is small enough so that some of them are masked by the telescope spider, dividing the pupil into disconnected domains. In particular, this problem will arise on the E-ELT.We have studied pure wavefront reconstruction on a Shack-Hartmann wavefront sensor, for a simplified AO system similar to VLT/SPHERE in size, with and without pupil fragmentation, and compared the performance of various wavefront reconstructors for different signal-to-noise ratios, using priors (minimum variance) or not (least-squares), and with different assumptions for the damaged wavefront measurements. The missing measurements have been either discarded (corresponding subapertures are not active), replaced by zeros, or interpolated by preserving the loop continuity property of the gradients (curl operator). Priors have been introduced using the FrIM (Fractal Iterative Method) algorithm. In our perfect conditions, we show that no method allows the full recovery from the pupil fragmentation, that minimum variance always gives the best performance, especially the one without any interpolation. On the opposite, the performance with least-squares somewhat improves when correcting for the missing measurements. In this latter case, preserving the curl property of the gradient is preferable only for very low measurement noise.
We study the impact of various telescope effects (like effect of phasing errors, missing segments, etc) on the performance of SCAO systems. This paper is using the E-ELT with 798 primary mirror segments. For example, we will show what kind of AO system (number of sub-apertures, frame-rate) is necessary to compensate for these effects, to get a fully seeing limited performance from the telescope.
GALACSI is the Adaptive Optics (AO) module that will serve the MUSE Integral Field Spectrograph. In Wide Field Mode it will enhance the collected energy in a 0.2”×0.2” pixel by a factor 2 at 750 nm over a Field of View (FoV) of 1’×1’ using the Ground Layer AO (GLAO) technique. In Narrow Field Mode, it will provide a Strehl Ratio of 5% (goal 10%) at 650 nm, but in a smaller FoV (7.5”×7.5” FoV), using Laser Tomography AO (LTAO). Before being ready for shipping to Paranal, the system has gone through an extensive testing phase in Europe, first in standalone mode and then in closed loop with the DSM in Europe. After outlining the technical features of the system, we describe here the first part of that testing phase and the integration with the AOF ASSIST (Adaptive Secondary Setup and Instrument Stimulator) testbench, including a specific adapter for the IRLOS truth sensor. The procedures for the standalone verification of the main system performances are outlined, and the results of the internal functional tests of GALACSI after full integration and alignment on ASSIST are presented.
For two years starting in February 2014, the AO modules GRAAL for HAWK-I and GALACSI for MUSE of the Adaptive Optics Facility project have undergone System Testing at ESO's Headquarters. They offer four different modes: NGS SCAO, LGS GLAO in the IR, LGS GLAO and LTAO in the visible. A detailed characterization of those modes was made possible by the existence of ASSIST, a test bench emulating an adaptive VLT including the Deformable Secondary Mirror, a star simulator and turbulence generator and a VLT focal plane re-imager. This phase aimed at validating all the possible components and loops of the AO modules before installation at the actual VLT that comprises the added complexity of real LGSs, a harsher non-reproducible environment and the adaptive telescope control.
In this paper we present some of the major results obtained and challenges encountered during the phase of System Tests, like the preparation of the Acquisition sequence, the testing of the Jitter loop, the performance optimization in GLAO and the offload of low-order modes from the DSM to the telescope (restricted to the M2 hexapod). The System Tests concluded with the successful acceptance, shipping, installation and first commissioning of GRAAL in 2015 as well as the acceptance and shipping of GALACSI, ready for installation and commissioning early 2017.
Over the last decade, adaptive optics has become essential in different fields of research including medicine and industrial applications. With this new need, the market of deformable mirrors has expanded a lot allowing new technologies and actuation principles to be developed. Several E-ELT instruments have identified the need for post focal deformable mirrors but with the increasing size of the telescopes the requirements on the deformable mirrors become more demanding. A simple scaling up of existing technologies from few hundred actuators to thousands of actuators will not be sufficient to satisfy the future needs of ESO. To bridge the gap between available deformable mirrors and the future needs for the E-ELT, ESO started a development program for deformable mirror technologies. The requirements and the path to get the deformable mirrors for post focal adaptive optics systems for the E-ELT is presented.
GALACSI is the Adaptive Optics (AO) system serving the instrument MUSE in the framework of the Adaptive Optics Facility (AOF) project. Its Narrow Field Mode (NFM) is a Laser Tomography AO (LTAO) mode delivering high resolution in the visible across a small Field of View (FoV) of 7.5" diameter around the optical axis. From a reconstruction standpoint, GALACSI NFM intends to optimize the correction on axis by estimating the turbulence in volume via a tomographic process, then projecting the turbulence profile onto one single Deformable Mirror (DM) located in the pupil, close to the ground.
In this paper, the laser tomographic reconstruction process is described. Several methods (virtual DM, virtual layer projection) are studied, under the constraint of a single matrix vector multiplication. The pseudo-synthetic interaction matrix model and the LTAO reconstructor design are analysed. Moreover, the reconstruction parameter space is explored, in particular the regularization terms.
Furthermore, we present here the strategy to define the modal control basis and split the reconstruction between the Low Order (LO) loop and the High Order (HO) loop. Finally, closed loop performance obtained with a 3D turbulence generator will be analysed with respect to the most relevant system parameters to be tuned.
The Adaptive Optics Facility is an ESO project aiming at converting Yepun, one of the four 8m telescopes in Paranal, into an adaptive telescope. This is done by replacing the current conventional secondary mirror of Yepun by a Deformable Secondary Mirror (DSM) and attaching four Laser Guide Star (LGS) Units to its centerpiece. In the meantime, two Adaptive Optics (AO) modules have been developed incorporating each four LGS WaveFront Sensors (WFS) and one tip-tilt sensor used to control the DSM at 1 kHz frame rate. The four LGS Units and one AO module (GRAAL) have already been assembled on Yepun.
Besides the technological challenge itself, one critical area of AOF is the AO control strategy and its link with the telescope control, including Active Optics used to shape M1. Another challenge is the request to minimize the overhead due to AOF during the acquisition phase of the observation.
This paper presents the control strategy of the AOF. The current control of the telescope is first recalled, and then the way the AO control makes the link with the Active Optics is detailed. Lab results are used to illustrate the expected performance. Finally, the overall AOF acquisition sequence is presented as well as first results obtained on sky with GRAAL.
The Laser Traffic Control System (LTCS) of the Paranal Observatory is the first component of the Adaptive Optics Facility (AOF, ) entering routine operations: a laser beam avoidance tool to support operations of an observatory equipped with five lasers and several laser-sensitive instruments, providing real-time information about ongoing and future collisions. LTCS-Paranal interfaces with ESO’s observing tools, OT and vOT. Altogether, this system allows the night operators to plan and execute their observations without worrying about possible collisions between the laser beam(s) and other lasersensitive equipment, aiming at a more efficient planning of the night, preventing time losses and laser-contaminated observations.
In this paper, we present an algorithm and supporting simulations results showing how a single conjugated AO system
can be used to detect a scalloping error occurring in the telescope. We show that when the scalloping error modes are
entered in the reconstruction modal basis, the Deformable Mirror shape can be used to estimate the scalloping error
through a simple matrix vector multiply. Temporal averaging allows to get rid of the atmospheric noise on the scalloping
measurement assuming a perfect “scalloping actuator” and to get a measurement accuracy of about 20nm rms.
The Adaptive Optics Facility (AOF) is a project that aims to transform the VLT UT4 into an adaptive telescope and
therefore to provide all its science instruments with turbulence corrected wavefronts. When used in its wide-field modes,
the AOF will allow to get a real time estimate of the turbulence distribution in the atmosphere, allowing an optimization
of the system correction. The so-called Wind Profiler (or Fourier Deconvolution) algorithm has been adapted to the AOF
configuration and validated through extensive tests. We show how it behaves under different modes and under typical
Paranal seeing conditions.
The Adaptive Optics Facility project is completing the integration of its systems at ESO Headquarters in Garching. The main test bench ASSIST and the 2nd Generation M2-Unit (hosting the Deformable Secondary Mirror) have been granted acceptance late 2012. The DSM has undergone a series of tests on ASSIST in 2013 which have validated its optical performance and launched the System Test Phase of the AOF. This has been followed by the performance evaluation of the GRAAL natural guide star mode on-axis and will continue in 2014 with its Ground Layer AO mode. The GALACSI module (for MUSE) Wide-Field-Mode (GLAO) and the more challenging Narrow-Field-Mode (LTAO) will then be tested. The AOF has also taken delivery of the second scientific thin shell mirror and the first 22 Watt Sodium laser Unit. We will report on the system tests status, the performances evaluated on the ASSIST bench and advancement of the 4Laser Guide Star Facility. We will also present the near future plans for commissioning on the telescope and some considerations on tools to ensure an efficient operation of the Facility in Paranal.
The Enhanced Resolution Imager and Spectrograph (ERIS) is the new Adaptive Optics based instrument for ESO’s VLT aiming at replacing NACO and SINFONI to form a single compact facility with AO fed imaging and integral field unit spectroscopic scientific channels. ERIS completes the instrument suite at the VLT adaptive telescope. In particular it is equipped with a versatile AO system that delivers up to 95% Strehl correction in K band for science observations up to 5 micron It comprises high order NGS and LGS correction enabling the observation from exoplanets to distant galaxies with a large sky coverage thanks to the coupling of the LGS WFS with the high sensitivity of its visible WFS and the capability to observe in dust embedded environment thanks to its IR low order WFS. ERIS will be installed at the Cassegrain focus of the VLT unit hosting the Adaptive Optics Facility (AOF). The wavefront correction is provided by the AOF deformable secondary mirror while the Laser Guide Star is provided by one of the four launch units of the 4 Laser Guide Star Facility for the AOF. The overall layout of the ERIS AO system is extremely compact and highly optimized: the SPIFFI spectrograph is fed directly by the Cassegrain focus and both the NIX’s (IR imager) and SPIFFI’s entrance windows work as visible/infrared dichroics. In this paper we describe the concept of the ERIS AO system in detail, starting from the requirements and going through the estimated performance, the opto-mechanical design and the Real-Time Computer design.
GALACSI is the Adaptive Optics (AO) modules of the ESO Adaptive Optics Facility (AOF) that will correct the wavefront delivered to the MUSE Integral Field Spectrograph. It will sense with four 40×40 subapertures Shack-Hartmann wavefront sensors the AOF 4 Laser Guide Stars (LGS), acting on the 1170 voice-coils actuators of the Deformable Secondary Mirror (DSM). GALACSI has two operating modes: in Wide Field Mode (WFM), with the four LGS at 64” off axis, the collected energy in a 0.2”×0.2” pixel will be enhanced by a factor 2 at 750 nm over a Field of View (FoV) of 1’×1’ using the Ground Layer AO (GLAO) technique. The other mode, the Narrow Field Mode (NFM), provides an enhanced wavefront correction (Strehl Ratio (SR) of 5% (goal 10%) at 650 nm) but in a smaller FoV (7.5”×7.5”), using Laser Tomography AO (LTAO), with the 4 LGS located closer, at 10” off axis. Before being shipped to Paranal, GALACSI will be first integrated and fully tested in stand-alone, and then moved to a dedicated AOF facility to be tested with the DSM in Europe. At present the module is fully assembled, its main functionalities have been implemented and verified, and AO system tests with the DSM are starting. We present here the main system features and the results of the internal functional tests of GALACSI.
Two algorithms were recently studied for C2n profiling from wide-field Adaptive Optics (AO) measurements on GeMS (Gemini Multi-Conjugate AO system). They both rely on the Slope Detection and Ranging (SLODAR) approach, using spatial covariances of the measurements issued from various wavefront sensors. The first algorithm estimates the C2n profile by applying the truncated least-squares inverse of a matrix modeling the response of slopes covariances to various turbulent layer heights. In the second method, the profile is estimated by deconvolution of these spatial cross-covariances of slopes. We compare these methods in the new configuration of ESO Adaptive Optics Facility (AOF), a high-order multiple laser system under integration. For this, we use measurements simulated by the AO cluster of ESO. The impact of the measurement noise and of the outer scale of the atmospheric turbulence is analyzed. The important influence of the outer scale on the results leads to the development of a new step for outer scale fitting included in each algorithm. This increases the reliability and robustness of the turbulence strength and profile estimations.
The Deformable Secondary Mirror (DSM) for the VLT ended the stand-alone electro-mechanical and optical acceptance process, entering the test phase as part of the Adaptive Optics Facility (AOF) at the ESO Headquarter (Garching). The VLT-DSM currently represents the most advanced already-built large-format deformable mirror with its 1170 voice-coil actuators and its internal metrology based on co-located capacitive sensors to control the shape of the 1.12m-diameter 2mm-thick convex shell. The present paper reports the final results of the electro-mechanical and optical characterization of the DSM executed in a collaborative effort by the DSM manufacturing companies (Microgate s.r.l. and A.D.S. International s.r.l.), INAF-Osservatorio Astrofisico di Arcetri and ESO. The electro-mechanical acceptance tests have been performed in the company premises and their main purpose was the dynamical characterization of the internal control loop response and the calibration of the system data that are needed for its optimization. The optical acceptance tests have been performed at ESO (Garching) using the ASSIST optical test facility. The main purpose of the tests are the characterization of the optical shell flattening residuals, the corresponding calibration of flattening commands, the optical calibration of the capacitive sensors and the optical calibration of the mirror influence functions.
As part of the preparation for the arrival of the MUSE instrument to the VLT, it was required to adapt the hosting
telescope (UT4) guide probe, to increase its back focal length. This is to allow enough space for the later deployment of
the MUSE Adaptive Optics module GALACSI, in-between the telescope adapter rotator and the instrument itself. The
UT guide probe is a critical component for the successful operation of the telescope, so its modification to increase the
telescope’s back focal length, while maintaining full compatibility with the existing operation model and other hardware,
was rather demanding.
The design, manufacture, assembly and test for the new supporting arm in the UT guiding probe is presented. It mixes
the use of novel materials (HB-CESIC® for the mirrors substrates) and state of the art manufacturing techniques (3D
printing mould production and rapid casting for the support structure), which allow producing easily a high performance
subsystem. Characterization of the system prior delivery to the telescope, its integration in the UT and results after
commissioning is presented. Its successful implementation has validated new manufacturing techniques that may prove
very useful for future instruments development.
The Enhanced Resolution Imager and Spectrograph (ERIS) is the next-generation instrument planned for the Very Large
Telescope (VLT) and the Adaptive Optics Facility (AOF)1. It is an AO assisted instrument that will make use of the
Deformable Secondary Mirror and the new Laser Guide Star Facility (4LGSF), and it is designed for the Cassegrain
focus of the telescope UT4. The project just concluded its conceptual design phase and is awaiting formal approval to
continue to the next phase. ERIS will offer 1-5 μm imaging and 1-2.5 μm integral field spectroscopic capabilities with
high Strehl performance. As such it will replace, with much improved single conjugated AO correction, the most
scientifically important and popular observing capabilities currently offered by NACO2 (diffraction limited imaging in JM
band, Sparse Aperture Masking and APP coronagraphy) and by SINFONI3, whose instrumental module, SPIFFI, will
be re-used in ERIS. The Cassegrain location and the performance requirements impose challenging demands on the
project, from opto-mechanical design to cryogenics to the operational concept. In this paper we describe the baseline
design proposed for ERIS and discuss these technical challenges, with particular emphasis on the trade-offs and the
novel solutions proposed for building ERIS.
The ESO Adaptive Optics Facility (AOF) will transform UT4 of the VLT into a laser driven adaptive telescope in which the corrective optics, specifically the deformable secondary mirror, and the four Laser Guide Star units are integrated. Three instruments, with their own AO modules to provide field selection capabilities and wavefront sensing, will make use of this system to provide a variety of observing modes that span from large field IR imaging with GLAO, to integral field visible spectroscopy with both GLAO and LTAO, to SCAO high Strehl imaging and spectroscopy. Each of these observing modes carries its specific demands on observing conditions. Optimal use of telescope night-time, with such a high in demand and versatile instruments suite, is mandatory to maintain and even improve upon the scientific output of the facility. This implies that the standard VLT model for operations must be updated to cover these partly new demands. In particular, we discuss three key aspects: (1) the need for an upgrade of the site monitoring facilities to provide the operators with real-time information on the environmental conditions, including the ground layer strength, and their evolution throughout the night; (2) a set of tools and procedures to effectively use these data to optimize the short-term scheduling (i.e. with granularity of one night) of the telescope and (3) the upgrade of the current laser beam avoidance software to better cope with the AOF operational scheme, where the four laser units are continuously operated as long as the atmospheric conditions allow.
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.
The project has completed the procurement phase and several large structures have been delivered to Garching
(Germany) and are being integrated (the AO modules GRAAL and GALACSI and the ASSIST test bench). The 4LGSF
Laser (TOPTICA) has undergone final design review and a pre-production unit has been built and successfully tested.
The Deformable Secondary Mirror is fully integrated and system tests have started with the first science grade thin shell
mirror delivered by SAGEM. The integrated modules will be tested in stand-alone mode in 2012 and upon delivery of
the DSM in late 2012, the system test phase will start. A commissioning strategy has been developed and will be updated
before delivery to Paranal. A substantial effort has been spent in 2011-2012 to prepare the unit telescope to receive the
AOF by preparing the mechanical interfaces and upgrading the cooling and electrical network. This preparation will also
simplify the final installation of the facility on the telescope.
A lot of attention is given to the system calibration, how to record and correct any misalignment and control the whole
facility. A plan is being developed to efficiently operate the AOF after commissioning. This includes monitoring a
relevant set of atmospheric parameters for scheduling and a Laser Traffic control system to assist the operator during the
night and help/support the observing block preparation.
The AOF project will transform one of the VLT UT into an adaptive telescope. This configuration presents new
challenges but also provides new opportunities for the integration of the Adaptive Optics in the global telescope control
scheme and performance improvement. In particular the Interaction Matrix between the Deformable Mirror and
Wavefront Sensor of the system cannot be measured on an artificial source, as there is no intermediate focal plane ahead
of the Deformable Mirror. The baseline for the AOF is to use a Pseudo-Pynthetic IM, i.e. computer-generated but finetuned
thanks to measured parameters of the system: Influence Functions, WFS characteristics, mis-alignments. This
paper presents the control strategy of the AOF, the simulation code that will be used to generate the PSIM for the AOF,
and the ideas for updating the Control Matrix depending on the estimation of the DM/WFS mis-registration.
The ESO Very Large Telescope Adaptive Optics Facility (VLT-AOF) will transform the VLT Unit Telescope 4 to an
Adaptive Telescope. In absence of an intermediate focus before the Adaptive Secondary in this Ritchey–Chrétien type
telescope and in order to reduce the testing and calibration of the system on-sky, ASSIST, The Adaptive Secondary
Setup and Instrument STimulator, was developed. It provides an off-sky testing facility for the ESO AOF and will
provide a full testing environment for three elements of the VLT Adaptive Optics Facility: the Deformable Secondary
Mirror (DSM) and the AO modules for MUSE and HAWK-I (GALACSI and GRAAL). ASSIST was delivered to ESO
Garching, where it was assembled and tested. Currently ASSIST is being integrated with the Deformable Secondary
Mirror, the first step in the full system testing of the two AO systems for the VLT AOF on ASSIST. This paper briefly
reviews the design and properties of ASSIST and reports on the first results of ASSIST in stand-alone mode.
The Enhanced Resolution Imager and Spectrograph (ERIS) is the next-generation instrument planned for the Very Large
Telescope (VLT) and the Adaptive Optics facility (AOF). It is an AO assisted instrument that will make use of the
Deformable Secondary Mirror and the new Laser Guide Star Facility (4LGSF), and it is planned for the Cassegrain focus
of the telescope UT4. The project is currently in its Phase A awaiting for approval to continue to the next phases.
The Adaptive Optics system of ERIS will include two wavefront sensors (WFS) to maximize the coverage of the
proposed sciences cases. The first is a high order 40x40 Pyramid WFS (PWFS) for on axis Natural Guide Star (NGS)
observations. The second is a high order 40x40 Shack-Hartmann WFS for single Laser Guide Stars (LGS) observations.
The PWFS, with appropriate sub-aperture binning, will serve also as low order NGS WFS in support to the LGS mode
with a field of view patrolling capability of 2 arcmin diameter. Both WFSs will be equipped with the very low read-out
noise CCD220 based camera developed for the AOF. The real-time reconstruction and control is provided by a SPARTA real-time platform adapted to support both WFS modes. In this paper we will present the ERIS AO system in all its main aspects: opto-mechanical design, real-time computer design, control and calibrations strategy. Particular emphasis will be given to the system performance obtained via dedicated numerical simulations.
The VLT Deformable secondary is planned to be installed on the VLT UT#4 as part of the telescope conversion into the
Adaptive Optics test Facility (AOF). The adaptive unit is based on the well proven contactless, voice coil motor
technology that has been already successfully implemented in the MMT, LBT and Magellan adaptive secondaries, and is
considered a promising technical choice for the forthcoming ELT-generation adaptive correctors, like the E-ELT M4 and
the GMT ASM. The VLT adaptive unit has been recently assembled after the completion of the manufacturing and
modular test phases. In this paper, we present the most relevant aspects of the system integration and report the
preliminary results of the electromechanical tests performed on the unit. This test campaign is a typical major step
foreseen in all similar systems built so far: thanks to the metrology embedded in the system, that allows generating time-dependent stimuli and recording in real time the position of the controlled mirror on all actuators, typical dynamic response quality parameters like modal settling time, overshoot and following error can be acquired without employing optical measurements. In this way the system dynamic and some aspect of its thermal and long term stability can be fully characterized before starting the optical tests and calibrations.
From the ardent bucklers used during the Syracuse battle to set fire to Romans’ ships to more contemporary piezoelectric
deformable mirrors widely used in astronomy, from very large voice coil deformable mirrors considered in future
Extremely Large Telescopes to very small and compact ones embedded in Multi Object Adaptive Optics systems, this
paper aims at giving an overview of Deformable Mirror technology for Adaptive Optics and Astronomy.
First the main drivers for the design of Deformable Mirrors are recalled, not only related to atmospheric aberration
compensation but also to environmental conditions or mechanical constraints. Then the different technologies available
today for the manufacturing of Deformable Mirrors will be described, pros and cons analyzed. A review of the
Companies and Institutes with capabilities in delivering Deformable Mirrors to astronomers will be presented, as well as
lessons learned from the past 25 years of technological development and operation on sky. In conclusion, perspective
will be tentatively drawn for what regards the future of Deformable Mirror technology for Astronomy.
GALACSI is one of the Adaptive Optics (AO) systems part of the ESO Adaptive Optics Facility (AOF). It will use the
VLT 4-Laser Guide Stars system, high speed and low noise WaveFront Sensor cameras (<1e-, 1000Hz) the
Deformable Secondary Mirror (DSM) and the SPARTA Real Time Computer to sharpen images and enhance faint
object detectability of the MUSE Instrument. MUSE is an Integral Field Spectrograph working at wavelengths from
465nm to 930nm. GALACSI implements 2 different AO modes; in Wide Field Mode (WFM) it will perform Ground
Layer AO correction and enhance the collected energy in a 0.2" by 0.2" pixel by a factor 2 at 750nm over a Field of
View (FoV) of 1' by 1'. The 4 LGSs and one tip tilt reference star (R-mag <17.5) are located outside the MUSE FoV.
Key requirements are to provide this performance and a very good image stability for a 1hour long integration time. In
Narrow Field Mode (NFM) Laser Tomography AO will be used to reconstruct and correct the turbulence for the center
field using the 4 LGSs at 15" off axis and the Near Infra Red (NIR) light of one reference star on axis for tip tilt and
focus sensing. In NFM GALACSI will provide a moderate Strehl Ratio of 5% (goal 10%) at 650nm. The NFM hosts
several challenges and many subsystems will be pushed to their limits. The opto mechanical design and error budgets
of GALACSI is described here.
We recall the design and present the development status of GRAAL, the Ground-layer adaptive optics assisted by Laser,
which will deliver wide-field (10 arcmin), enhanced images to the HAWK-I instrument on the VLT, with an improved
seeing. GRAAL is an adaptive optics module, part of the Adaptive optics facility (AOF), 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.
GRAAL is in the laboratory in Europe and the integration of its laser guide-star optics is completed. The first wave-front
sensor camera will be ready for its integration in the coming weeks, allowing the first system tests to start.
The resolution of ground-based telescopes is dramatically limited by the atmospheric turbulence.. Adaptative optics
(AO) is a real-time opto-mechanical approach which allows to correct for the turbulence effect and to reach the ultimate
diffraction limit astronomical telescopes and their associated instrumentation.
Nevertheless, the AO correction is never perfect especially when it has to deal with large Field of View (FoV). Hence, a
posteriori image processing really improves the final estimation of astrophysical data. Such techniques require an
accurate knowledge of the system response at any position in the FoV
The purpose of this work is then the estimation of the AO response in the particular case of the MUSE  /GALACSI
 instrument (a 3D mult-object spectrograph combined with a Laser-assisted wide field AO system which will be
installed at the VLT in 2013). Using telemetry data coming from both AO Laser and natural guide stars, a Point Spread
Function (PSF) is derived at any location of the FoV and for every wavelength of the MUSE spectrograph.
This document presents the preliminary design of the MUSE WFM PSF reconstruction process. The various hypothesis
and approximations are detailed and justified. A first description of the overall process is proposed. Some alternative
strategies to improve the performance (in terms of computation time and storage) are described and have been
implemented. Finally, after a validation of the proposed algorithm using end-to-end models, a performance analysis is
conducted (with the help of a full end-to-end model). This performance analysis will help us to populate an exhaustive
error budget table.
ASSIST, The Adaptive Secondary Setup and Instrument STimulator, is being developed to provide a testing facility for
the ESO Adaptive Optics Facility (AOF). It will allow the off-telescope testing of three elements of the VLT AOF; the
Deformable Secondary Mirror (DSM) and the AO systems for MUSE and HAWK-I (GALACSI and GRAAL). The core
of ASSIST consists of a 2-mirror setup (AM1-AM2) allowing the on-axis test of the DSM in interferometric mode.
However, during the initial stages of ASSIST integration, DSM would not be present. This makes the task of aligning
AM1-AM2 to within an accuracy of 0.05mm/1 arcmin rather challenging. A novel technique known as Shack-Hartmann
method has been developed and tested in the lab for this purpose. A Shack Hartmann wavefront sensor will be used to
measure the mis-alignment between AM1-AM2 by recording the coma and astigmatism in the presence of large
spherical aberration introduced because of tilt/decenter of AM2 with respect to AM1. Thereafter, 20 optical components
including lenses, flat mirrors and beam-splitter cubes divided into five sub-assemblies should be aligned to AM1-AM2-
DSM axis which ultimately passes through the mechanical axis of large AMOS rotator.
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
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.
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
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.
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.
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.
ASSIST: The Adaptive Secondary Setup and Instrument STimulator is the test setup for the verification and calibration
of three elements of the VLT Adaptive Optics Facility.; the Deformable Secondary Mirror (DSM) the AO system for
MUSE and HAWK-I (GALACSI and GRAAL). In the DSM testing mode the DSM will be tested using both
interferometry and fast wave front sensing. In full AO mode, ASSIST will allow testing of the AO systems under
realistic atmospheric conditions and optically equivalent to the conditions on the telescope. ASSIST is nearing its final
design review and in this paper we present the current optical and mechanical design of ASSIST. In this paper we
highlight some of the specific aspects of ASSIST that we are developing for ASSIST.
ESO has initiated in June 2004 a concept of Adaptive Optics Facility. One unit 8m telescope of the VLT is upgraded
with a 1.1 m convex Deformable Secondary Mirror and an optimized instrument park. The AO modules GALACSI and
GRAAL will provide GLAO and LTAO corrections forHawk-I and MUSE. A natural guide star mode is provided for
commissioning and maintenance at the telescope. The facility is completed by a Laser Guide Star Facility launching 4
LGS from the telescope centerpiece used for the GLAO and LTAO wavefront sensing. A sophisticated test bench called
ASSIST is being designed to allow an extensive testing and characterization phase of the DSM and its AO modules in
Europe. Most sub-projects have entered the final design phase and the DSM has entered Manufacturing phase. First light
is planned in the course of 2012 and the commissioning phases should be completed by 2013.
ASSIST - The Adaptive Secondary Setup and Instrument STimulator is a test setup to verify the operation of three
elements of the VLT Adaptive Optics Facility, namely the Deformable Secondary Mirror (DSM) and the two AO
systems using this DSM, the AO system for the visible light integral field spectrograph MUSE (GALACSI) and the AO
system for the IR wide field imager HAWK-I (GRAAL). To support the testing of these elements, ASSIST will provide
both an interferometry setup for testing the DSM as well as a full atmospheric turbulence simulator and star simulator to
mimic the conditions at the telescope. To test the instruments using the DSM, the output beam is matched the output
beam of the VLT telescope, including the correct exit-pupil and high-quality imaging and a similar hardware interface is
provided. Since one of the modes to be verified is nearly diffraction limited, also the thermal and vibrational stability
are very important, with strong constraints on both the mechanical as well as the optical design.
NAOS is the first adaptive optics system installed at the VLT 8m telescopes. It was designed, manufactured and tested by a french Consortium under an ESO contract, to provide compensated images to the high angular resolution IR spectro-imaging camera (CONICA) in the 1 to 5 μm spectral range. It is equipped with a 185 actuator deformable mirror, a tip/tilt mirror and two wavefront sensors, one in the visible and one in the near IR spectral range. It has been installed in November at the Nasmyth focus B of the VLT UT4. During the first light run in December 2001, NAOS has delivered a Strehl ratio of 50 under average seeing conditions for bright guide stars. The diffraction limit of the telescope has been achieved at 2.2 μm. The closed loop operation has been very robust under bad seeing conditions. It was also possible to obtain a substantial correction with mV=17.6 and mK=13.1 reference stars. The on-sky acceptance tests of NAOS-CONICA were completed in May 2002 and the instrument will be made available to the European astronomical community in October by ESO. This paper describes the system and present the on-sky performance in terms of Strehl ratio, seeing conditions and guide star magnitude.
NAOS is the adaptive optics system to be installed at one of the Nasmyth focus of the VLT. It was designed and manufactured by a French Consortium to provide compensated images to the high angular resolution IR spectro-imaging camera (CONICA) in the 1 to 5 micrometer spectral range. For bright sources, NAOS will achieve a Strehl ratio of 70% under average seeing conditions. It is equipped with a 185 actuator deformable mirror, a tip/tilt mirror and two wavefront sensors, one in the visible and one in the near IR. All the components of NAOS have been delivered and the integration phase is in progress since the beginning of 2000. After extensive tests and performance verifications in France, the system will be shipped to Chile by the end of 2000. The first light at the VLT is foreseen in the beginning of 2001.
The Real Time Computer RTC is a key component of the Nasmyth Adaptive Optics System, controlling the 185 actuators of the deformable mirror from a 144 Shack-Hartmann subapertures wavefront sensor at a maximum frequency of 500 Hz. It also provides additional capabilities such as real time optimization of the control loop which is the warranty for NAOS to achieve a very good Strehl Ratio in a broad magnitude range (Mv equals 8 up to 18), on-line turbulence and performance estimations and finally capability to store and process the data necessary to the off-line PSF reconstruction algorithm. This RTC is also designed to be easily upgraded as for Laser Guide Star. Moreover all softwares can be easily adapted to control a curvature sensor as well as the hardware which can be used with the two types of wave front sensors.
This paper presents new concepts for a Fringe Sensor Unit (FSU) optimized for high accuracy and low flux operation. This concept has been studied for the VLTI/PRIMA instrument in the H (and K) bands. To optimize both photon use and accuracy, an efficient spatial achromatic discrete modulation is chosen. For optical path difference measurements, most of the photons are used in a single polychromatic quadrature while the adjustable remaining part is dispersed for simultaneous group delay tracking. Integration time can be very short since no moving device is used. This FSU can also be turned to a classical two quadratures FSU if needed, for differential delay or visibility measurements. Optical designs for these FSUs are proposed. These simple designs are also very well suited to future space instruments. Theoretical performance and simulation results are finally given and compared to other existing devices.
We report on first observation run with the Achromatic Interfero Coronagraph (AIC) developed at Observatoire de la Cote d'Azure, France. Observations took place last Fall at Observatoire de Haute Provence with the 1.52 m telescope equipped at that time with adaptive optics. The AIC is an imaging device providing the nulling of a star without nulling the close environment of this star. Nulling results from a destructive interference process. Morphological features located as close to the star as the first angular Airy ring can be detected, thus breaking a limitation of the classical Lyot coronagraphs. The objectives of the observation run is to demonstrate that the AIC can image faint companions very close to the diffraction limit with ground-based telescope. After a short reminding of the principle of the AIC, conditions of observations are reported and first coronagraphed-images are shown. Finally limitations are discussed and improvements to carry on are described.
NAOS is the adaptive optics system to be installed at one of the Nasmyth foci of the very large telescope (VLT). It will provide compensated image to the high angular resolution IR spectro-imaging camera which covers the 1-5 micrometers spectral bands. our French consortium is the sub-contractor of ESO for the design, manufacturing, integration and test of NAOS. For bright sources, the specification is to reach 70 percent Strehl ratio under average seeing conditions. Two wavefront sensors, one in the visible spectral range and one in the near IR spectral range, will equip the adaptive optics system. We foresee to obtained the first light at the VLT unit telescope 1 in mid-2000.
From the local wavefront slope measurement given by a Shack Hartmann wavefront sensor (SH), it is possible to evaluate the decentering aberrations introduced by optical system misalignments. These slopes can be expressed as a function of the centered system aberrations and of the optical axis displacements in the image and pupil planes. After calibration of the wavefront sensor, the system alignment can be, for small aberrations, automatically controlled. The validity of the concept was proved on a representative observation system.
The COME-ON+ adaptive optics system was set up on the ESO 3.6-meter telescope for two technical runs (in December 1992 and April 1993) and is now routinely used for astronomical observations. This system is an upgrade of the COME-ON adaptive optics prototype system. During the technical runs, images were recorded in the V, I, J, K and L' spectral bands. Currently, the best resolution obtained is 0.1' in H (1.65 micrometers ) under bad seeing conditions (seeing > 1' and averaged wind speed > 10 m/s) and reference star magnitudes of 6 to 8. The corresponding Strehl ratio is 35%. 70% Strehl ratio was obtained at 2.2 micrometers (K band). At 0.9 micrometers (I band), in the partial correction regime, the resolution is of the order of 0.2' for 0.8' seeing and 10 m/s averaged wind speed. The optimized modal control has been used on faint reference stars. The limiting magnitude (in V band) for wavefront sensing has been measured to 14 and 15 depending on the spectral type of the reference star and the seeing conditions for a low frequency tip-tilt correction.
A bimorph mirror seems to be low voltage, large strokes device which can be used as a correction mirror in an adaptive optics system for infrared applications. A few theoretical results are recalled and have been used to develop a numerical method to solve the displacements of a bimorph mirror supplied by a distribution of voltages. An example is given which involves seven electrodes; comparisons with theoretical and other numerical results are achieved.
A bimorph mirror seems to be a low voltage, large strokes device which can be used
as a correction mirror in an adaptive optics system for infrared applications.
A few theoretical results are recalled and have been used to develop a numerical
method to solve the displacements of a bimorph mirror supplied by a distribution of
voltages. An example is given which involves seven electrodes ; comparisons with
theoretical and other numerical results are achieved.
Same paper has been presented during the SPIE's 90 Symposium on Astronomical
Telescopes and Instrumentation for the 21st Century in February 1990.