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.
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 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.
GeMS, the Gemini Laser Guide Star Multi-Conjugate Adaptive Optics facility system, has seen first light in December 2011, and has already produced images with H band Strehl ratio in excess of 35% over fields of view of 85x85 arcsec, fulfilling the MCAO promise. In this paper, we report on these early results, analyze trends in performance, and concentrate on key or novel aspects of the system, like centroid gain estimation, on-sky non common path aberration estimation. We also present the first astrometric analysis, showing very encouraging results.
It is a widely accepted conjecture that the width of the incoherent halo in an adaptive optics point-spread function (PSF) should decrease with the level of correction. Using end-to-end simulations we prove that this is not the case and the halo is actually increasing in width, albeit at a decreasing overall brightness level as must be the case with increasing correction. The simulations span the cases of: seeing-limited, partial-, and high-order adaptive-optics (AO) correction. We show the relationship between the theory of partially-developed speckle and the observed statistical behavior of on-axis PSF intensity. Finally, we check the results of the simulations with real data obtained using the 3.5m Starfire Optical
Range telescope located in New Mexico, US.
The effects of pupil motion on retinal imaging are studied in this paper. Involuntary eye or head movements
are always present in the imaging procedure, decreasing the output quality and preventing a more detailed
diagnostics. When the image acquisition is performed using an adaptive optics (AO) system, substantial gain is
foreseen if pupil motion is accounted for. This can be achieved using a pupil tracker as the one developed by
Imagine Eyes R®, which provides pupil position measurements at a 80Hz sampling rate. In any AO loop, there
is inevitably a delay between the wavefront measurement and the correction applied to the deformable mirror,
meaning that an optimal compensation requires prediction. We investigate several ways of predicting pupil
movement, either by retaining the last value given by the pupil tracker, which is close to the optimal solution in
the case of a pure random walk, or by performing position prediction thanks to auto-regressive (AR) models with
parameters updated in real time. We show that a small improvement in prediction with respect to predicting
with the latest measured value is obtained through adaptive AR modeling. We evaluate the wavefront errors
obtained by computing the root mean square of the difference between a wavefront displaced by the assumed
true position and the predicted one, as seen by the imaging system. The results confirm that pupil movements
have to be compensated in order to minimize wavefront errors.
GeMS (the Gemini Multi-conjugated adaptive optics System) is a facility instrument for the Gemini-South
telescope. It will deliver a uniform, diffraction-limited image quality at near-infrared (NIR) wavelengths over an
extended FoV or more than 1 arcmin across. GeMS is a unique and challenging project from the technological
point of view and because of its control complexity. The system includes 5 laser guide stars, 3 natural guide
stars, 3 deformable mirrors optically conjugated at 0, 4.5 and 9km and 1 tip-tilt mirror. After 10 years since
the beginning of the project, GeMS is finally reaching a state in which all the subsystems have been received,
integrated and, in the large part, tested. In this paper, we report on the progress and current status of the
different sub-systems with a particular emphasis on the calibrations, control and optimization of the AO bench.
Myst is the Gemini MCAO System (GeMS) high level control GUI. It is written in yorick, python and C. In this
paper, we review the software architecture of Myst and its primary purposes, which are many: Real-time display,
high level diagnostics, calibrations, and executor/sequencer of high level actions (closing the loop, coordinating
Modeling adaptive optics (AO) systems is crucial to understanding their performance and a key aid in their
design. The Giant Magellan Telescope (GMT) is planning three AO modes at first light: natural guide star AO,
ground-layer AO and laser tomography AO. This paper describes how a modified version of YAO, an open-source
general-purpose AO simulation tool written in Yorick, is used to simulate the GMT AO modes. The simulation
tool was used to determine the piston segment error for the GMT. In addition, we present a comparison of
different turbulence simulation approaches.
The Laser Adaptive Optics system of the 6.5 m MMT telescope has now been commissioned with Ground Layer
Adaptive Optics operations as a tool for astronomical science. In this mode the wavefronts sampled by each of five laser
beacons are averaged, leading to an estimate of the aberration in the ground layer. The ground layer is then compensated
by the deformable secondary mirror at 400 Hz. Image quality of
0.2-0.3 arc sec is delivered in the near infrared bands
from 1.2-2.5 μm over a field of view of 2 arc minutes. Tomographic wavefront sensing tests in May 2010 produced open
loop data necessary to streamline the software to generate a Laser Tomography Adaptive Optics (LTAO) reconstructor.
In addition, we present the work being done to achieve optimal control PID wavefront control and thus increase the
disturbance rejection frequency response for the system. Finally, we briefly describe plans to mount the ARIES near
infrared imager and echelle spectrograph, which will support the 2 arc min ground-layer corrected field and will exploit
the diffraction limit anticipated with LTAO.
We perform simulations of a single-conjugated adaptive optics (SCAO) system for an E-ELT-like telescope
using a pyramid wavefront sensor (PWFS) and an on-axis NGS. The advantage of this WFS has already been
demonstrated, being currently preferred in many AO systems where high signal sensitivity is critical. The main
objective of this work is to evaluate the performance of such SCAO system under different control parameters
(loop gain, modulation, truncated SVD mode), sensing wavelengths, atmospheric coherence scales and NGS
magnitudes. Always adopting K as the science band, we have verified that the overall performance tends to
be poorer as the sensing wavelength becomes shorter. The loop gain optimal range is dependent on the SVD
truncation threshold used to build the command matrix, and a
non-modulated PWFS produces in general poorer
results when compared to modulated cases, being this especially true for the R- sensing band. The default
atmospheric model adopted was a von Karman with r0=0.13m (at 500nm) and outer scale of 25m, but poorer
and better seeing conditions have also been tested. The long-exposure Strehls are better in larger modulations.
The telescope pupil has a central obstruction of 28% but no spiders were included. We also show results for the
incidence of different photon fluxes at the PWFS detector.
Simulations of adaptive optics (AO) for the European extremely large telescope (EELT) are presented. For Shack-Hartmann wavefront sensors for the laser guide star (LGS) based systems, the simulations show that without the Rayleigh fratricide effect, central projection of the laser is preferable to side projection, the correlation or
matched filter centroiding algorithms offer superior performance to a traditional center-of-gravity approach, the optimum sampling of the detector is approximately 1.5 pixels per FWHM of the non-elongated spot, and that at least 10×10 pixels are required. The required number of photo-detection events from the LGS per frame per
subaperture is of the order of 1000. Correction of segmentation errors with a Shack-Hartmann wavefront sensor
(WFS) has also been investigated; atmospheric turbulence dominates these segmentation errors. The pyramid
WFS is also simulated for the EELT, showing that modulation of the pyramid will be necessary.