The COMPASS platform was designed to meet the need for high-performance for the simulation of AO systems. Taking advantage of the specific hardware architecture of the GPU, the COMPASS tool allows the AO scientist to obtain adequate execution speeds and to conduct large simulation campaigns scaled to the E-ELT dimensioning for a variety of AO flavors from SCAO to MOAO. On the latest GPU architecture (NVIDA Volta), execution speeds of several hundreds of short exposure PSF per second can be achieved for a SCAO system on the E-ELT, making the COMPASS platform a real-time end-to-end simulation tool. In this paper, we provide a full description of the critical physical models used in the simulation pipeline, review a range AO system configurations that can be addressed with COMPASS and report on the time to solution obtained for this systems. Scalability over multiple GPUs and multiple generations of GPUs is also discussed.
MICADO is the European ELT first-light imager, working in the near-infrared at the telescope diffraction limit. Provided by MAORY, the ELT first-light adaptive optics module (AO), MCAO will be the primary AO mode of MICADO, driving the design of the instrument. MICADO will also come with a SCAO capability. Developed under MICADO’s responsibility and jointly by MICADO and MAORY, SCAO will be the first AO mode to be tested at the telescope, in a phased approach of the AO integration at the ELT. The MICADO-MAORY SCAO preliminary design review (PDR) will occur in November 2018. We present here different activities and results we have had in the past two years preparing this PDR, covering several fields (opto-mechanics, electronics, real-time and control software, integration and tests, AO simulations and performance, prototyping) and the different SCAO subsystems (pyramid wavefront sensor, calibration unit, real-time computer, dichroic and the so-called Green Doughnut which hosts the SCAO assembly as well as the MAORY MCAO natural guide star wavefront sensors).
Six Laser Guide Stars (LGS) are included in the design of the European Extremely Large Telescope (ELT), with all of its current instruments taking advantage of them using Shack-Hartmann (SH) wavefront sensors (WFS). However, this implementation raises new issues related to the unprecedented elongation that results from the perspective effect combined to the thickness of the sodium layer. In order to investigate wavefront sensing with an elongated LGS on a SH WFS, we are taking advantage of the presence of the multi-object adaptive optics demonstrator CANARY on the William Herschel Telescope (WHT), in La Palma island, that was upgraded with a sodium LGS WFS for our experiment. The LGS is generated by ESO’s transportable Wendelstein LGS unit and the elongation is obtained by positioning the laser launch telescope 40 meters away from the WHT. With this experiment we are able to measure wavefronts using an elongated LGS WFS. In this paper, we present results obtained during the latest run of observations in September 2017. In these results is comprised an error breakdown of wavefront measurement on elongated LGS. The performances of several centroiding methods are compared thanks to this error breakdown. Additionally, we take advantage of varying observation conditions with respect to seeing and sodium profile to establish the robustness of the different centroiding methods. Finally, these performances are evaluated for different SH designs, to explore which compromises can be reached with respect to pixel scale and sub-aperture field of view.
CANARY is a wide-field AO on-sky test facility which has been operated annually on the 4.2m William Herschel Telescope since 2010. CANARY has the stated goal of testing and demonstrating AO technologies that are critical for ELT AO performance. It has seen four distinct phases where new AO technologies have been developed and demonstrated, including NGS MOAO in 2010 (phase A), Rayleigh LGS and NGS MOAO in 2012 and 2013 (phase B, with LGS commissioning in 2011), LTAO operation in 2014 and 2015, and finally operation with a single Sodium laser guide star launched far off axis in 2016 and 2017 (phase D). By launching this laser guide star 40m off axis, extremely elongated laser guide star spots are created in the CANARY LGS Shack-Hartmann wavefront sensor. Therefore, the 7×7 sub-apertures of CANARY can be used to test wavefront sensing performance of a sub-pupil of the ELT located furthest from the laser launch axis. We present an overview of CANARY in its phase D configuration. Depending on where in the sky the LGS is pointing, the projected baseline between the on-axis LGS wavefront sensor and the laser launch location, as seen by the wavefront sensor, will vary from about 20-40m, allowing us to artificially generate different degrees of elongation. Additionally, the well sampled CANARY sub-apertures have 30×30 pixels each and a 20 arcsecond field of view, using an OCAM2S EMCCD camera. This means that by shrinking sub-apertures, and optionally by binning pixels, we are able to investigate different pixel scales and fields of view for the ELT systems, thus determining the optimal design parameters. Here we discuss the closed loop tests that were performed to investigate the effect of spot truncation and extreme elongation. We include different correlation techniques, including standard FFT-based correlation, brute force correlation and correlation by difference squared. We also mention dynamic and automatic updates of the correlation reference images while the AO loop is engaged that have previously been reported. The matched filter algorithm is also mentioned, with a pointer to our prior on-sky investigations. We give our recommendation for the ELT wavefront sensing algorithm of choice, and our evidence based reasons for this recommendation, which may come as a surprise to some. Finally we also present the future experiments to be performed with CANARY, give details of the OPTICON funded programme which enables the hosting of AO experiments on CANARY, allowing the AO community to get involved.
Extremely Large Telescopes are making Pyramid Wavefront Sensors (PWFS) the preferred engineering choice for Adaptive Optics designs, such as the MICADO camera SCAO subsystem currently developed at LESIA. A major PWFS issue is the so-called Optical Gain (OG) effect: PWFSs experience a nonlinearity-induced sensitivity reduction – of 60% or worse at the fitting error on standard atmospheric conditions – which degrades as the turbulence residual increases. OG affects system performance, jeopardizes loop stability and prevents efficient non-common path aberration compensation. We investigate a modal approach to OG impact mitigation, and investigate its impact on nonlinearity error depending on the AO control basis. We evidence that scalar gain compensation of the OG is insufficient on high order systems, as the high spatial frequency range spanned covers high OG value discrepancies over the controlled basis. We quantify the performance improvements obtained with OG modal compensation by end-to-end numerical simulations. Finally, we propose a modelization of OG modal compensation coefficients, in order to allow their computation on-the-fly provided telemetry of the immediate turbulence conditions is available.
In preparation of future multiobject spectrographs (MOS) whose one of the major role is to provide an extensive statistical studies of high redshifted galaxies surveyed, the demonstrator CANARY has been designed to tackle technical challenges related to open-loop adaptive optics (AO) control with jointed Natural Guide Star and Laser Guide Star tomography. We have developed a point spread function (PSF) reconstruction algorithm dedicated to multiobject adaptive optics systems using system telemetry to estimate the PSF potentially anywhere in the observed field, a prerequisite to postprocess AO-corrected observations in integral field spectroscopy. We show how to handle off-axis data to estimate the PSF using atmospheric tomography and compare it to a classical approach that uses on-axis residual phase from a truth sensor observing a natural bright source. We have reconstructed over 450 on-sky CANARY PSFs and we get bias/1-σ standard-deviation (std) of 1.3/4.8 on the H-band Strehl ratio (SR) with 92.3% of correlation between reconstructed and sky SR. On the full-width at half-maximum, we get, respectively, 2.94 mas, 19.9 mas, and 88.3% for the bias, std, and correlation. The reference method achieves 0.4/3.5/95% on the SR and 2.71 mas/14.9 mas/92.5% on the FWHM for the bias/std/correlation.
Laser Guide Stars (LGS) have greatly increased the sky-coverage of Adaptive Optics (AO) systems. Due to the up-link turbulence experienced by LGSs, a Natural Guide Star (NGS) is still required, limiting sky-coverage. A method has recently been presented that promises to determine the LGS uplink tip-tilt in tomographic LGS AO systems by using the fact that each LGS Wave Front Sensor (WFS) in a tomographic AO system observes the uplink path of other LGSs. Such a technique has the potential to greatly increase the sky-coverage of Multi- Object, Laser Tomographic and Multi-Conjugate AO systems by allowed further off-axis NGS tip-tilt stars to be used for correction. Here we use an approach based on phase gradient covariance matrices to create on-sky capable tomographic reconstructors that account for some tip-tilt from LGS WFSs. We present analysis of open loop wave front sensor data from the CANARY Multi-Object AO demonstrator, providing early validation for the technique.
MICADO will equip the E-ELT with a first light capability for diffraction limited imaging at near-infrared wavelengths. The instrument’s observing modes focus on various flavours of imaging, including astrometric, high contrast, and time resolved. There is also a single object spectroscopic mode optimised for wavelength coverage at moderately high resolution. This contribution provides an overview of the key functionality of the instrument, outlining the scientific rationale for its observing modes. The interface between MICADO and the adaptive optics system MAORY that feeds it is summarised. The design of the instrument is discussed, focusing on the optics and mechanisms inside the cryostat, together with a brief overview of the other key sub-systems.
CANARY is the Multi-Object Adaptive Optics (MOAO) pathfinder for the future MOAO-assisted Integral-Field Units (IFU) proposed for Extremely Large Telescopes (ELT). The MOAO concept relies on tomographically reconstructing the turbulence using multiple measurements along different lines of sight.
Tomography requires the knowledge of the statistical turbulence parameters, commonly recovered from the system telemetry using a dedicated profiling technique. For demonstration purposes with the MOAO pathfinder CANARY, this identification is performed thanks to the Learn & Apply (L&A) algorithm, that consists in model-fitting the covariance matrix of WFS measurements dependant on relevant parameters: Cn2(h) profile, outer scale profile and system mis-registration.
We explore an upgrade of this algorithm, the Learn 3 Steps (L3S) approach, that allows one to dissociate the identification of the altitude layers from the ground in order to mitigate the lack of convergence of the required empirical covariance matrices therefore reducing the required length of data time-series for reaching a given accuracy. For nominal observation conditions, the L3S can reach the same level of tomographic error in using five times less data frames than the L&A approach.
The L3S technique has been applied over a large amount of CANARY data to characterize the turbulence above the William Herschel Telescope (WHT). These data have been acquired the 13th, 15th, 16th, 17th and 18th September 2013 and we find 0.67"/8.9m/3.07m.s−1 of total seeing/outer scale/wind-speed, with 0.552"/9.2m/2.89m.s−1 below 1.5 km and 0.263"/10.3m/5.22m.s−1 between 1.5 and 20 km. We have also determined the high altitude layers above 20 km, missed by the tomographic reconstruction on CANARY , have a median seeing of 0.187" and have occurred 16% of observation time.
The goal of the COMPASS project was to bring together the efforts of the actors from the French AO community (PHASE partnership), with the participation of the Maison de la Simulation, around the collaborative development of a numerical platform for AO, optimized and based on the use of graphics processing units (GPU). This platform allows today to lead the design studies of AO modules addressing all of the first generation instrumentation of the E-ELT. In this paper, we provide a status update of the platform and the long term maintenance and development plan.
To approach optimal performance advanced Adaptive Optics (AO) systems deployed on ground-based telescopes must have accurate knowledge of atmospheric turbulence as a function of altitude. Stereo-SCIDAR is a high-resolution stereoscopic instrument dedicated to this measure. Here, its profiles are directly compared to internal AO telemetry atmospheric profiling techniques for CANARY (Vidal et al. 20141), a Multi-Object AO (MOAO) pathfinder on the William Herschel Telescope (WHT), La Palma. In total twenty datasets are analysed across July and October of 2014. Levenberg-Marquardt fitting algorithms dubbed Direct Fitting and Learn 2 Step (L2S; Martin 20142) are used in the recovery of profile information via covariance matrices - respectively attaining average Pearson product-moment correlation coefficients with stereo-SCIDAR of 0.2 and 0.74. By excluding the measure of covariance between orthogonal Wavefront Sensor (WFS) slopes these results have revised values of 0.65 and 0.2. A data analysis technique that combines L2S and SLODAR is subsequently introduced that achieves a correlation coefficient of 0.76.
The use of sodium laser guide star for Extremely Large Telescopes (ELT) adaptive optics systems is a key concern due to the perspective effect that produces elongated images in the Shack-Hartmann pattern. In order to assess the feasibility of using an elongated sodium beacon on an ELT, an on-sky experiment reproducing the extreme off-axis launch conditions of the European ELT is scheduled for summer and autumn 2016. The experiment will use the demonstrator CANARY installed on the William Herschel Telescope and the ESO transportable 20W CW fiber laser, embedded in the Wendelstein LGS unit. We will discuss here the challenges this experiment addresses as well as the details of its implementation and the derivation of the error budget.
CANARY is an open-loop tomographic adaptive optics (AO) demonstrator that was designed for use at the 4.2m William Herschel Telescope (WHT) in La Palma. Gearing up to extensive statistical studies of high redshifted galaxies surveyed with Multi-Object Spectrographs (MOS), the demonstrator CANARY has been designed to tackle technical challenges related to open-loop Adaptive-Optics (AO) control with mixed Natural Guide Star (NGS) and Laser Guide Star (LGS) tomography.
We have developed a Point Spread Function (PSF)-Reconstruction algorithm dedicated to MOAO systems using system telemetry to estimate the PSF potentially anywhere in the observed field, a prerequisite to deconvolve AO-corrected science observations in Integral Field Spectroscopy (IFS). Additionally the ability to accurately reconstruct the PSF is the materialization of the broad and fine-detailed understanding of the residual error contributors, both atmospheric and opto-mechanical.
In this paper we compare the classical PSF-r approach from Véran (1) that we take as reference on-axis using the truth-sensor telemetry to one tailored to atmospheric tomography by handling the off-axis data only.
We've post-processed over 450 on-sky CANARY data sets with which we observe 92% and 88% of correlation on respectively the reconstructed Strehl Ratio (SR)/Full Width at Half Maximum (FWHM) compared to the sky values. The reference method achieves 95% and 92.5% exploiting directly the measurements of the residual phase from the Canary Truth Sensor (TS).
MICADO is the E-ELT first-light imager, working at the diffraction limit in the near-infrared. Multi-conjugate adaptive optics (MCAO) will be the primary AO mode of MICADO, driving the design of the instrument. It will be provided by MAORY, the E-ELT first-light AO module. MICADO will also come with a SCAO capability, jointly developed by MICADO and MAORY. SCAO will be the first AO mode to be tested at the telescope, in a phased approach of AO integration at the E-ELT.
We present in the following the MICADO-MAORY SCAO specifications, the current SCAO prototyping activities at LESIA for E-ELT scale pyramid wavefront sensor (WFS) and real-time computer (RTC), our activities on end-to-end AO simulations and the current preliminary design of SCAO subsystems. We finish by presenting the implementation and current design studies for the high-contrast imaging mode of MICADO, which will make use of the SCAO correction offered to the instrument.
CANARY is an on-sky Laser Guide Star (LGS) tomographic AO demonstrator in operation at the 4.2m William Herschel Telescope (WHT) in La Palma. From the early demonstration of open-loop tomography on a single deformable mirror using natural guide stars in 2010, CANARY has been progressively upgraded each year to reach its final goal in July 2015. It is now a two-stage system that mimics the future E-ELT: a GLAO-driven woofer based on 4 laser guide stars delivers a ground-layer compensated field to a figure sensor locked tweeter DM, that achieves the final on-axis tomographic compensation. We present the overall system, the control strategy and an overview of its on-sky performance.
We present in this paper the current simulation results of the single-conjugate adaptive optics (SCAO) mode of the wide-field imager MICADO. MICADO is a near-IR camera for the European ELT, featuring a wide field (75"), spectroscopic, and coronagraphic capabilities. It has been chosen by ESO as one of the two first-light instruments. MICADO will be optimized for the multi-conjugate adaptive optics module MAORY and will also work in SCAO mode. This SCAO mode will provide MICADO a high-level, on-axis correction, making use of the adaptive secondary M4 in the telescope. It is shown here that the on-axis compensation level reaches Strehl ratios (SR) of the order of 0.70 in K band under median seeing condition, and quickly degrades with field angle. However, despite the important leak of the light from the core towards the halo, we demonstrate how the point spread function (PSF) remains topped with an Airy-like pattern even at low SR below 0.02. This known effect, due to the large telescope aperture, was already shown in past studies. We show here how dependent from the outer scale value this effect is, and we study how the presence of this peak allows the instrument to preserve astrometric capabilities even far out of the isoplanatic patch domain.
The Gemini Multi-conjugate adaptive optics System (GeMS) at the Gemini South telescope in Cerro Pachon is the first sodium Laser Guide Star (LGS) adaptive optics (AO) system with multiple guide stars. It uses five LGSs and two deformable mirrors (DMs) to measure and compensate for distortions induced by atmospheric turbulence. After its 2012 commissioning phase, it is now transitioning into regular operations. Although GeMS has unique scientific capabilities, it remains a challenging instrument to maintain, operate and upgrade. In this paper, we summarize the latest news and results. First, we describe the engineering work done this past year, mostly during our last instrument shutdown in 2013 austral winter, covering many subsystems: an erroneous reconjugation of the Laser guide star wavefront sensor, the correction of focus field distortion for the natural guide star wavefront sensor and engineering changes dealing with our laser and its beam transfer optics. We also describe our revamped software, developed to integrate the instrument into the Gemini operational model, and the new optimization procedures aiming to reduce GeMS time overheads. Significant software improvements were achieved on the acquisition of natural guide stars by our natural guide star wavefront sensor, on the automation of tip-tilt and higher-order loop optimization, and on the tomographic non-common path aberration compensation. We then go through the current operational scheme and present the plan for the next years. We offered 38 nights in our last semester. We review the current system efficiency in term of raw performance, completed programs and time overheads. We also present our current efforts to merge GeMS into the Gemini base facility project, where night operations are all reliably driven from our La Serena headquarter, without the need for any spotter. Finally we present the plan for the future upgrades, mostly dedicated toward improving the performance and reliability of the system. Our first upgrade called NGS2, a project lead by the Australian National University, based a focal plane camera will replace the current low throughput natural guide wavefront sensor. On a longer term, we are also planning the (re-)integration of our third deformable mirror, lost during the early phase of commissioning. Early plans to improve the reliability of our laser will be presented.
In this article we revisit a subject that has partly already been examined in previous studies: the behavior of tomographic reconstructors in adaptive optics systems, facing to an atmospheric profile (C2n(h)) different from the one they've been optimized for. We develop a new approach for that. The current usual approach is to simulate the performance of the reconstructor when slightly varying the C2n(h) profile around a nominal one, and show how far the deviation may go. This has the disadvantage that, as the parameter space for potential errors on the C2n(h) profile is basically infinite, it is particularly uneasy to span. Our approach consists in deriving a sort of sensitivity function, that we call vertical error distribution (VED), from the knowledge of any tomographic reconstructor. This function can be computed even for non-tomographic reconstructors, ground-layers reconstructors, single-conjugate AO reconstructors, etc. In any case, it allows us to derive the error when applied to a particular C2n(h) profile, have a direct, global visualization of the error variation with layer altitude, for any number at any altitude. This also allows us to understand what a given reconstructor is sensitive to, at what altitudes or altitude range, or explain why some GLAO reconstructors may perform better than optimized MMSE tomographic reconstructors if low-altitude layers pop up. We also discuss the case of ELTs and apply our approach to large scale reconstructors.
Multi-object adaptive optics (MOAO) is a novel adaptive optics (AO) technique for wide-field multi-object spectrographs (MOS). MOAO aims at applying dedicated wavefront corrections to numerous separated tiny patches spread over a large field of view (FOV), limited only by that of the telescope. The control of each deformable mirror (DM) is done individually using a tomographic reconstruction of the phase based on measurements from a number of wavefront sensors (WFS) pointing at natural and artificial guide stars in the field. We have developed a novel hybrid, pseudo-analytical simulation scheme, somewhere in between the end-to- end and purely analytical approaches, that allows us to simulate in detail the tomographic problem as well as noise and aliasing with a high fidelity, and including fitting and bandwidth errors thanks to a Fourier-based code. Our tomographic approach is based on the computation of the minimum mean square error (MMSE) reconstructor, from which we derive numerically the covariance matrix of the tomographic error, including aliasing and propagated noise. We are then able to simulate the point-spread function (PSF) associated to this covariance matrix of the residuals, like in PSF reconstruction algorithms. The advantage of our approach is that we compute the same tomographic reconstructor that would be computed when operating the real instrument, so that our developments open the way for a future on-sky implementation of the tomographic control, plus the joint PSF and performance estimation. The main challenge resides in the computation of the tomographic reconstructor which involves the inversion of a large matrix (typically 40 000 × 40 000 elements). To perform this computation efficiently, we chose an optimized approach based on the use of GPUs as accelerators and using an optimized linear algebra library: MORSE providing a significant speedup against standard CPU oriented libraries such as Intel MKL. Because the covariance matrix is symmetric, several optimization schemes can be envisioned to speedup even further the computation. Optimizing the speed of the reconstructor computation is of major interest not only for the design study of MOAO instruments, but also for future routine operations of the system as the reconstructor has to be updated regularly to cope for atmospheric variability.
CANARY is an on-sky Laser Guide Star (LGS) tomographic AO demonstrator that has been in operation at the 4.2m William Herschel Telescope (WHT) in La Palma since 2010. In 2013, CANARY was upgraded from its initial configuration that used three off-axis Natural Guide Stars (NGS) through the inclusion of four off-axis Rayleigh LGS and associated wavefront sensing system. Here we present the system and analysis of the on-sky results obtained at the WHT between May and September 2014. Finally we present results from the final ‘Phase C’ CANARY system that aims to recreate the tomographic configuration to emulate the expected tomographic AO configuration of both the AOF at the VLT and E-ELT.
CANARY is the multi-object adaptive optics (MOAO) on-sky demonstrator developed by Durham University and LESIA Observatoire de Paris, in the perspective of the E-ELT. Since 2013, CANARY has been operating with 3 off-axis NGS and 4 off-axis Rayleigh LGS and compensating for one on-axis NGS observed with a near IR camera and the Truth Sensor (TS) for diagnostic purpose. In this paper, we present the tomographic performance of CANARY during the runs in 2013. We propose a detailed analysis of the tomographic error leading to the establishment of the CANARY wave-front error budget. In particular we are able to evaluate the tomographic error for each altitude in the atmosphere for a given reconstructor by modelling a set of one-layer covariance matrices. This tool allows us to understand the tradeoffs to be made in the building of the tomographic reconstructor. We present two methods for the wavefront error budget computation. The DTI one uses input system parameters and open loop WFS slopes to estimate the error in a number of independent terms. The DMTS method directly uses the Truth Sensor measurements to estimate the error. We show a good agreement between the two approaches making us confident in our modelling of the instrument. We derive estimations of the Strehl ratio from the error variance and compare them to the recorded IR image Strehl ratio. We find a good agreement between the two, hence validating our wavefront error analysis. Finally we present an on-sky validation of the tomographic reconstruction using LGS based on GLAO and MOAO data. We also quantify the gain brought by the LGS, comparing results obtained in MOAO with 3 NGS and with or without LGS in the wavefront measurements.
We present in this paper an overview of the single-conjugate adaptive optics (SCAO) module of the wide-field imager MICADO. MICADO is a near-IR camera for the European ELT, featuring a wide field (75"), spectroscopic and coronagraphic capabilities. It has been chosen by ESO as one of the two first-light instruments. MICADO will be optimized for the multi-conjugate adaptive optics module MAORY and will also work in SCAO mode. This SCAO mode will provide MICADO with a high-level, on-axis correction, making use of the M4 adaptive mirror in the telescope. We present first the current design of the different subsystems of the SCAO module (namely the optical relay interfacing MICADO to the telescope in its SCAO mode, the wavefront sensor, the real-time computer and the high contrast imaging). We then present the adaptive optics and coronagraphic simulations. The following section is devoted to the presentation of the project organization. We end with the conclusions and perspectives of the project.
The identification of spatial covariance matrices is required in adaptive optics in order to perform tomographic
reconstruction with optimal estimators. We use on-sky measurements from Canary, the on-sky demonstrator
of MOAO for EAGLE, to study the statistical convergence of the spatial covariance of Shack-Hartmann measurements.
We describe a new, faster, analytical approximated model for this spatial covariance, and finally
bring into light a new procedure for model identification, reducing the tomographic error. We quantify the gain
brought by the new approach on both numerical simulations and on-sky data.
We characterize the performance of deformable mirrors for use in open-loop regimes. This is especially relevant for Multi Object Adaptive Optics (MOAO), or for closed-loop schemes that require improved accuracies. Deformable mirrors are usually characterized by standard parameters, such as influence functions, linearity, hysteresis, etc. We show that these parameters are insufficient for characterizing open-loop performance and that a deeper analysis of the mirror's behavior is then required. The measurements on the deformable mirrors were performed in 2007 on the AO test bench of the Meudon observatory, SESAME.
CANARY is an on-sky demonstrator adaptive optics (AO) system that in 2010 provided the first on-sky demonstration
of open-loop tomographic adaptive optics correction using natural guide stars (NGS). Phase B of the CANARY
experiment aims to extend the instrument from its original configuration by also measuring wavefronts from four offaxis
Rayleigh laser guide stars (LGS). This upgrade allows CANARY to perform tomographic wavefront sensing over a
2.5arcminute field of view using any mix of up to seven off-axis wavefront sensors (four LGS and three NGS)
simultaneously. AO correction within CANARY is performed on-axis along a single line of sight using a 52-actuator
deformable mirror being controlled in open-loop. Here we give an overview of the Phase B LGS system, discuss the
calibration of a mixed NGS/LGS tomographic system and present the recent laboratory and on-sky results from the
Phase B commissioning.
Many concepts of Wide Field AO (WFAO) systems are under development, especially for Extremely Large Tele scopes (ELTs) instruments. Multi-Object Adaptive Optics (MOAO) is one of these WFAO concepts, well suited to high redshifts galaxies observations in very wide Field of View (FoV). The E-ELT instrument EAGLE will use this approach. CANARY, the on-sky pathfinder for MOAO, has obtained the first compensated images on Natural Guide Stars (NGSs) at the William Herschel Telescope in September 2010. We present in this paper numerical and experimental validations of a Linear Quadratic Gaussian (LQG) control. This is an appealing strategy that provides an optimal control in the sense of minimum residual phase variance. It also provides a unified formalism that allows accounting for multi WaveFront Sensors (WFSs) channels, both on Laser Guide Stars (LGSs) and NGSs, and for various disturbance sources (turbulence, vibrations). We show how the specific MOAO CANARY configuration can be embedded in a state-space framework. We present experimental laboratory validations that demonstrate the gain brought by tomographic LQG control for CANARY, together with comparative simulations. Model identification necessary for a robust on-sky operation is discussed.
We present in this paper an analysis of several tip-tilt on-sky data registered on adaptive optics systems installed on different telescopes (Gemini South, William Herschel Telescope, Large Binocular Telescope, Very Large Tele scope, Subaru). Vibration peaks can be detected, and it is shown that their presence and location may vary, and that their origin is not always easy to determine. Mechanical solution that have been realized to mitigate vibrations are presented. Nevertheless, residual vibrations may still affect the instruments' performance, ranging from narrow high frequency vibration peaks to wide low frequency windshake-type perturbations. Power Spectral Densities (PSDs) of on-sky data are presented to evidence these features. When possible, indications are given regarding the gain in performance that could be achieved with adequate controllers accounting for vibration mitigation. Two examples of controller identification and design illustrate their ability to compensate for various types of disturbances (turbulence, windshake, vibration peaks, ...),showing a significant gain in performance.
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.
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.
EAGLE is a multi-object 3D spectroscopy instrument currently under design for the 42-metre European Extremely Large
Telescope (E-ELT). Precise requirements are still being developed, but it is clear that EAGLE will require (~100 x 100
actuator) adaptive optics correction of ~20 - 60 spectroscopic subfields distributed across a ~5 arcminute diameter field
of view. It is very likely that LGS will be required to provide wavefront sensing with the necessary sky coverage. Two
alternative adaptive optics implementations are being considered, one of which is Multi-Object Adaptive Optics
(MOAO). In this scheme, wavefront tomography is performed using a set of LGS and NGS in either a completely open-loop
manner, or in a configuration that is only closed-loop with respect to only one DM, probably the adaptive M4 of the
E-ELT. The fine wavefront correction required for each subfield is then applied in a completely open-loop fashion by
independent DMs within each separate optical relay. The novelty of this scheme is such that on-sky demonstration is
required prior to final construction of an E-ELT instrument. The CANARY project will implement a single channel of an
MOAO system on the 4.2m William Herschel Telescope. This will be a comprehensive demonstration, which will be
phased to include pure NGS, low-order NGS-LGS and high-order woofer-tweeter NGS-LGS configurations. The LGSs
used for these demonstrations will be Rayleigh systems, where the variable range-gate height and extension can be used
to simulate many of the LGS effects on the E-ELT. We describe the requirements for the various phases of MOAO
demonstration, the corresponding CANARY configurations and capabilities and the current conceptual designs of the
EAGLE is an instrument under conceptual study for the European Extremely Large Telescope (E-ELT). EAGLE will be
installed at the Gravity Invariant Focal Station of the E-ELT, covering a field of view between 5 and 10 arcminutes. Its
main scientific drivers are the physics and evolution of high-redshift galaxies, the detection and characterization of first-light
objects and the physics of galaxy evolution from stellar archaeology. The top level requirements of the instrument
call for 20 spectroscopic channels in the near infrared, assisted by Adaptive Optics. Several concepts of the Target
Acquisition sub-system have been studied and are briefly presented. Multi-Conjugate Adaptive Optics (MCAO) over a
segmented 5' field has been evaluated and compared to Multi-Object Adaptive Optics (MOAO). The latter has higher
performance and is easier to implement, and is therefore chosen as the baseline for EAGLE. The paper provides a status
report of the conceptual study, and indicates how the future steps will address the instrument development plan due to be
completed within a year.