The Learn and Apply tomographic reconstructor coupled with the pseudo open-loop control scheme shows promising results in simulation for multi-conjugate adaptive optics systems. We motivate, derive, and demonstrate the inclusion of a predictive step in the Learn and Apply tomographic reconstructor based on frozen-flow turbulence assumption. The addition of this predictive step provides an additional gain in performance, especially at larger wave-front sensor exposure periods, with no increase of online computational burden. We provide results using end-to-end numerical simulations for a multi-conjugate adaptive optics system for an 8m telescope based on the MAVIS system design.
KEYWORDS: Visible radiation, James Webb Space Telescope, Observatories, Adaptive optics, Large telescopes, Spectrographs, Spatial resolution, Hubble Space Telescope, Telescopes
A consortium of several Australian and European institutes – together with the European Southern Observatory (ESO) – has initiated the design of MAVIS, a Multi-Conjugate Adaptive Optics (MCAO) system for the ground- based 8-m Very Large Telescope (VLT). MAVIS (MCAO-assisted Visible Imager and Spectrograph) will deliver visible images and integral field spectrograph data with 2-3x better angular resolution than the Hubble Space Telescope, making it a powerful complement at visible wavelengths to future facilities like the space-based James Webb Space Telescope and the 30 to 40m-class ground-based telescopes currently under construction, which are all targeting science at near-infrared wavelengths. MAVIS successfully passed its Phase A in May 2020. We present the motivations, requirements, principal design choices, conceptual design, expected performance and an overview of the exciting science enabled by MAVIS.
The MCAO Assisted Visible Imager and Spectrograph (MAVIS) is a facility-grade visible MCAO instrument, currently under development for the Adaptive Optics Facility at the VLT. The adaptive optics system will feed both an imager and an integral field spectrograph, with unprecedented sky coverage of 50% at the Galactic Pole. The imager will deliver diffraction-limited image quality in the V band, cover a 30" x 30" field of view, with imaging from U to z bands. The conceptual design for the spectrograph has a selectable field-of-view of 2.5" x 3.6", or 5" x 7.2", with a spatial sampling of 25 or 50 mas respectively. It will deliver a spectral resolving power of R=5,000 to R=15,000, covering a wavelength range from 380 - 950 nm. The combined angular resolution and sensitivity of MAVIS fill a unique parameter space at optical wavelengths, that is highly complementary to that of future next-generation facilities like JWST and ELTs, optimised for infrared wavelengths. MAVIS will facilitate a broad range of science, including monitoring solar system bodies in support of space missions; resolving protoplanetary- and accretion-disk mechanisms around stars; combining radial velocities and proper motions to detect intermediate-mass black holes; characterising resolved stellar populations in galaxies beyond the local group; resolving galaxies spectrally and spatially on parsec scales out to 50 Mpc; tracing the role of star clusters across cosmic time; and characterising the first globular clusters in formation via gravitational lensing. We describe the science cases and the concept designs for the imager and spectrograph.
This paper presents a preliminary analysis of the first results we have obtained from the adaptive optics systems built for EOS 1.8 m telescope at Mount Stromlo. This presentation focuses on the single-camera stereo-SCIDAR for monitoring the atmospheric seeing. We briefly summarize the system, describe its on-sky performance during commissioning, compare results to numerical simulations and evaluate the remaining challenges going into the future.
Space debris in low Earth orbit (LEO) below 1500 km is becoming an increasing threat to spacecrafts. To manage the threat, we are developing systems to improve the ground-based tracking and imaging of space debris and satellites. We also intend to demonstrate that it is possible to launch a high-power laser that modifies the orbits of the debris. However, atmospheric turbulence makes it necessary to use adaptive optics with such systems. When engaging with objects in LEO, the objects are available only a limited amount of time. During the observation window, the object has to be acquired and performance of all adaptive optics feedback loops optimised. We have implemented a high-level adaptive optics supervision tool to automatise time-consuming tasks related to calibration and performance monitoring. This paper describes in detail the current features of our software.
Adaptive Optics (AO) systems rely on atmospheric turbulence models in order to reduce the effect of wave-front aberrations on image quality. Due to the nature of turbulence, these models can exploit shift-invariant structures without a severe loss in generality. The resulting subset of possible state-matrices is efficiently characterised for identification using Quadratic Programming (QP). Additionally, the initial assumption of shift-invariance is relaxed in order to accommodate for the boundary effect of finite-pupils.
Adaptive Optics (AO) improves the image quality of ground-based telescopes, by compensating in real-time for the blurring effects of atmospheric turbulence. AO systems of future Extremely Large Telescopes (ELTs) will have to operate at much bigger scales (in terms of degrees of freedom) and faster control rates (in terms of loop frequency) to realise their full potential. We have investigated and simulated an AO control methodology to stream pixels “as they come” using a rolling-shutter sCMOS camera to reconstruct 2D images. Compared to a traditional global shutter implementation, the initial results indicate the rolling shutter can reduce control loop latency by a factor of two to four, using existing hardware. This means we can detect twice the number of photons while sampling twice as slowly. Nevertheless, significant technical challenges remain in implementing the rolling functionality, especially when integrating off-the-shelf software and hardware, which is often constricted by a closed-source code base. Furthermore, as the rolling shutter readout is asynchronous, questions remain about coupling and aliasing of telescope vibrations into the imaging system, causing distortions of time and space. If successfully implemented in practice, the rolling shutter approach has the potential to allow astronomers and engineers to capture better scientific observations closer to the diffraction limit.
We report on the design and initial laboratory testing of the Adaptive Optics Imaging (AOI) system. AOI has been developed by the Research School of Astronomy and Astrophysics (RSAA) at the Australian National University (ANU), in partnership with the Space Environment Research Centre (SERC), for imaging satellites and debris in low Earth orbit (LEO) and geostationary orbit (GEO). From AO corrected images we will resolve features greater than 50 cm allowing size, shape and orientation characterisation.
We report on the conceptual design study done for the Ground Layer Adaptive Optics system of the ULTIMATE-Subaru project. This is an ambitious instrument project, providing GLAO correction in a square field of view of 14 arcmin on a side, aiming to deliver improved seeing at the near infrared wavelength. Its client instruments are an imager and multi-IFU spectrograph at Cassegrain and a Multi-Object spectrograph at Nasmyth. In this paper, we introduce the ULTIMATE-Subaru project overview and its science case and report the results of the GLAO performance prediction based on the numerical simulation and conceptual design of the wavefront sensor system.
As space debris in lower Earth orbits are accumulating, techniques to lower the risk of space debris collisions must be developed. Within the context of the Space Environment Research Centre (SERC), the Australian National University (ANU) is developing an adaptive optics system for tracking and pushing space debris. The strategy is to pre-condition a laser launched from a 1.8 m telescope operated by Electro Optics Systems (EOS) on Mount Stromlo, Canberra and direct it at an object to perturb its orbit. Current progress towards implementing this experiment, which will ensure automated operation between the telescope and the adaptive optics system, will be presented.
We present the status of the site-characterisation campaign at Mount Stromlo Observatory. The main goal of the project is to aid the development and operation of new adaptive optics (AO) systems for space debris tracking and pushing as well as satellite imaging. The main method we use for the characterisation is based on the SCIntillation Detection And Ranging (SCIDAR) technique. We have designed a unique version of the SCIDAR instrument: a stereo-SCIDAR system that uses a roof prism to separate beams from a double-star system to obtain two isolated pupil images on a single detector. The instrument is installed on the 1.8 m telescope of Electro-Optic Systems (EOS), sharing facilities with the adaptive optics systems we are currently building. The SCIDAR instrument will be operated intermittently, weather and availability permitting, until sufficient amount of data has been collected to characterise the site. This paper reports the current status of the project: we have recently started the commissioning phase and obtained first measurements with the instrument.
Satellite tracking and imaging is conducted by the ANU Research School of Astronomy and Astrophysics (RSAA) and Electro-Optic Systems at Mount Stromlo as part of the Space Environment Management Cooperative Research Centre to support debris tracking. To optimally design adaptive optics systems for those applications, it is important to know the atmospheric profile, i.e. how the turbulence is distributed as a function altitude. We have designed a new stereo-SCIDAR instrument1 to conduct a site characterisation campaign at Mount Stromlo site. This paper summarises our current progress: specifications, design choices and post-processing techniques. In particular, we compare two different post-processing algorithms for stereo-SCIDAR, using simulated data cubes. One of the codes is implemented by the RSAA, the other by the Centre for Advanced Instrumentation, University of Durham. The comparison shows that the current implementations of both codes produce decent results. However, we can see potential for further improvements.
Satellite tracking and imaging is conducted by the ANU Research School of Astronomy and Astrophysics and Electro-Optic Systems (EOS) at Mount Stromlo Observatory, Canberra, Australia, as part of the Space Environment Management Cooperative Research Centre (SERC) to support the development in space situational awareness. Atmospheric turbulence leads to distortions in the measured data. Adaptive optics (AO) systems counteract those distortions and improve the resolution of the tracking and imaging systems. To assist in the design of the AO systems, we need to gather information on the atmosphere at Mount Stromlo: r0, τ 0, and the turbulence Cn2 profile. With the SCIntillation Detection And Ranging (SCIDAR) Technique the scintillation of two stars is measured and their autocorrelation function is computed, providing a measurement of the turbulence profile. This technique usually uses one detector recording the two images of the stars simultaneously. However, the images overlap leading to an underestimation of the Cn2 values. The introduction of stereo-SCIDAR1 over- comes this issue by separating the two stars and imaging them on two separate image sensors. To reduce costs, we introduce a new stereo-SCIDAR system separating the beams from the two stars, but using only one single detector. This has been shown for a Low Layer SCIDAR (LOLAS) system with wide double stars (200 arcsec). We investigate this technique by detecting the scintillation patterns of double stars with separation from 10 to 25 arcsec, allowing some flexibility in the altitude span and resolution, while retaining a simple optical setup. We selected a low noise sCMOS camera as the imager. We show the current design of this system and investigate its feasibility for further development.
Non-Common Path Errors (NCPEs) are the dominant factor limiting the performance of current astronomical high-contrast imaging instruments. If uncorrected, the resulting quasi-static speckle noise floor limits coronagraph performance to a raw contrast of typically 10−4, a value which does not improve with increasing integration time. The coronagraphic Modal Wavefront Sensor (cMWS) is a hybrid phase optic which uses holographic PSF copies to supply focal-plane wavefront sensing information directly from the science camera, whilst maintaining a bias-free coronagraphic PSF. This concept has already been successfully implemented on-sky at the William Herschel Telescope (WHT), La Palma, demonstrating both real-time wavefront sensing capability and successful extraction of slowly varying wavefront errors under a dominant and rapidly changing atmospheric speckle foreground. In this work we present an overview of the development of the cMWS and recent first light results obtained using the Leiden EXoplanet Instrument (LEXI), a high-contrast imager and high-dispersion spectrograph pathfinder instrument for the WHT.
We investigate methods to calibrate the non-common path aberrations at an adaptive optics system having a wavefront-correcting device working with an extremely high resolution (larger than 150x150 correcting elements). We use focal-plane images collected successively, the corresponding phase-diversity information and numerically efficient algorithms to calculate the required wavefront updates. Different approaches are considered in numerical simulations, and laboratory experiments are shown to confirm the results. We compare the performances of the standard Gerchberg-Saxton algorithm, Fast and Furious (use of small-phase assumption to take advantage of linearisation) and recently proposed phase-retrieval methods based on convex optimisation. The results indicate that the calibration task is easiest with algorithms similar to Fast and Furious, at least in the framework we considered.
KEYWORDS: Point spread functions, Wavefronts, Data transmission, Turbulence, Computer simulations, Zernike polynomials, Chemical elements, Tolerancing, Computing systems, Control systems
In this paper we give a new wavefront estimation technique that overcomes the main disadvantages of the phase
diversity (PD) algorithms, namely the large computational complexity and the fact that the solutions can get
stuck in a local minima. Our approach gives a good starting point for an iterative algorithm based on solving a
linear system, but it can also be used as a new wavefront estimation method. The method is based on the Born
approximation of the wavefront for small phase aberrations which leads to a quadratic point-spread function
(PSF), and it requires two diversity images. First we take the differences between the focal plane image and each
of the two diversity images, and then we eliminate the constant object, element-wise, from the two equations.
The result is an overdetermined set of linear equations for which we give three solutions using linear least squares
(LS), truncated total least squares (TTLS) and bounded data uncertainty (BDU). The last two approaches are
suited when considering measurements affected by noise. Simulation results show that the estimation is faster than conventional PD algorithms.
The increasing requirement on the performance of optical instruments leads to more complex optical systems including
active optical components. The role of these components is to correct for environmental influences on the instrument and
reduce manufacturing and alignment residuals. We describe a method that can be used to design and operate instruments
with active components that are not necessarily located in the pupil. After the optical system is designed, the next step is
to analyse the available degrees of freedom (DOF), select the best set and include them in the active component. By
performing singular value decomposition (SVD) and regularization of the sensitivity matrix, the most efficient DOF for
the active component can be calculated. In operation of the instrument, the wavefront at the pupil plane is reconstructed
from phase diversity (PD); a metrology having minimal impact on instrument design. Information from SVD, forward
and reverse optimization are used to model the process, explore the parameter space and acquire knowledge on
convergence. The results are presented for a specific problem.
We investigate the potential of phase-diversity (PD) and Gerchberg-Saxton (GS) algorithms in the calibration of
active instruments. A set of images is recorded with the focal-plane scientific camera, each image having a known
and unique defocus. The phase-retrieval algorithms are used, with those images, to estimate the non-common
path aberration that needs to be compensated by correct alignment of the instrument. We demonstrate by
numerical simulations that such algorithms, in particular GS, are sufficient detection methods to fully correct
wavefronts with an rms error at least up to 6 rad — but this requires several iterative correction stages.
We show experimental results demonstrating the feasibility of an extremely fast sequential phase-diversity (SPD)
algorithm for point sources. The algorithm can be implemented on a typical adaptive optics (AO) system to
improve the wavefront reconstruction beyond the capabilities of a wavefront sensor by using the information
from the imaging camera. The algorithm is based on a small-phase approximation enabling fast numerical
implementation, and it finds the optimal wavefront correction by iteratively updating the deformable mirror.
Our experiments were made at an AO-setup with a 37 actuator membrane mirror, and the results show that
the algorithm finds an optimal image quality in 5–10 iterations, when the initial wavefront errors are typical
non-common path aberrations having a magnitude of 1–1.5 rad rms. The results are in excellent agreement with
corresponding numerical simulations.
We propose a new approach for the joint estimation of aberration parameters and unknown object from diversity
images with applications in imaging systems with extended objects as astronomical ground-based observations
or solar telescopes. The motivation behind our idea is to decrease the computational complexity of the conventional
phase diversity (PD) algorithm and avoid the convergence to local minima due to the use of nonlinear
estimation algorithms. Our approach is able to give a good starting point for an iterative algorithm or it can
be used as a new wavefront estimation method. When the wavefront aberrations are small, the wavefront can be approximated with a linear term which leads to a quadratic point-spread function (PSF) in the aberration parameters. The presented approach involves recording two or more diversity images and, based on the before mentioned approximation estimates the aberration parameters and the object by solving a system of bilinear equations, which is obtained by subtracting from each diversity image the focal plane image. Moreover, using the quadratic PSFs gives improved performance to the conventional PD algorithm through the fact that the gradients of the PSFs have simple analytical formulas.
We present a promising approach to the extremely fast sensing and correction of small wavefront errors in adaptive optics systems. As our algorithm's computational complexity is roughly proportional to the number of actuators, it is particularly suitable to systems with 10,000 to 100,000 actuators. Our approach is based on sequential phase diversity and simple relations between the point-spread function and the wavefront error in the case of small aberrations. The particular choice of phase diversity, introduced by the deformable mirror itself, minimizes the wavefront error as well as the computational complexity. The method is well suited for high contrast astronomical imaging of point sources such as the direct detection and characterization of exoplanets around stars, and it works even in the presence of a coronagraph that suppresses the diffraction pattern. The accompanying paper in these proceedings by Korkiakoski et al. describes the performance of the algorithm using numerical simulations and laboratory tests.
ESO and a large European consortium completed the phase-A study of EPICS, an instrument dedicated to exoplanets
direct imaging for the EELT. The very ambitious science goals of EPICS, the imaging of reflected light of mature gas
giant exoplanets around bright stars, sets extremely strong requirements in terms of instrumental contrast achievable. The
segmented nature of an ELT appears as a very large source of quasi-static high order speckles that can impair the
detection of faint sources with small brightness contrast with respect to their parent star. The paper shows how the
overall system has been designed in order to maximize the efficiency of quasi-static speckles rejection by calibration and
post-processing using the spectral and polarization dependency of light waves. The trade-offs that led to the choice of the
concepts for common path and diffraction suppression system is presented. The performance of the instrument is
predicted using simulations of the extreme Adaptive Optics system and polychromatic wave-front propagation through
the various optical elements.
EPICS is a project for a high contrast imaging instrument dedicated to direct imaging of exoplanets with the
European Extremely Large Telescope. Its conceptual design study phase has finished at the early 2010, and
we show here its end-to-end extreme adaptive optics simulation results. The simulations have been made using
conventional, well-known but numerically intensive computation techniques (full Fourier diffraction model of a
WFS and wavefront reconstruction with matrix-vector-multiplication). Many error sources important for XAO
are considered: chromaticity effects, M1 segment mis-figure, pupil rotation, WFS misregistration, telescope jitter
and spiders. The results confirm that a raw contrast of 10-5 is reached at 20 mas, and 10-7-10-6 at 200-500 mas.
This is in agreement with our analytic estimations and EPICS
top-level requirements.
Presently, dedicated instruments at large telescopes (SPHERE for the VLT, GPI for Gemini) are about to discover and
explore self-luminous giant planets by direct imaging and spectroscopy. The next generation of 30m-40m ground-based
telescopes, the Extremely Large Telescopes (ELTs), have the potential to dramatically enlarge the discovery space
towards older giant planets seen in reflected light and ultimately even a small number of rocky planets. EPICS is a
proposed instrument for the European ELT, dedicated to the detection and characterization of Exoplanets by direct
imaging, spectroscopy and polarimetry. ESO completed a phase-A study for EPICS with a large European consortium
which - by simulations and demonstration experiments - investigated state-of-the-art diffraction and speckle suppression
techniques to deliver highest contrasts. The paper presents the instrument concept and analysis as well as its main
innovations and science capabilities. EPICS is capable of discovering hundreds of giant planets, and dozens of lower
mass planets down to the rocky planets domain.
We present simulation results of modal sensitivity compensation, a method to improve pyramid wavefront sensor
(P-WFS) performance in high wavefront distortion regime. It has been shown that an alternative reference signal
subtraction is able to dramatically improve the algorithm performance (0.30 in terms of Strehl ratio at 1.6 &mgr;m).
In addition, we illustrate the limitations of the algorithm: high spatial sampling of the measured phase is needed
and robustness issues are confronted at the low flux regimes. In a comparison with a Shack-Hartmann sensor
the sensitivity compensated P-WFS is shown to perform at least as well (outside the high noise cases).
One of the main science objectives of the European ELT is the direct imaging of extrasolar planets. The large aperture of
the telescope has the potential to significantly enlarge the discovery space towards older gas giant exo-planets seen in
reflected light. In this paper, we give an overview of the EPICS system design strategy during the phase A study. In
order to tackle the critical limitations to high contrast, extensive end-to-end simulations will be developed since the start
to test different scenarios and guide the overall design.
KEYWORDS: Monte Carlo methods, Adaptive optics, Control systems, Signal to noise ratio, Zernike polynomials, Computer simulations, Actuators, Telescopes, Real-time computing, Sensors
Next generation adaptive-optics systems (AO) have unprecedented complexity. The proposed number of degrees-of-freedom has considerably increased, putting the focus on the real-time processing capabilities. Second generation instrumentation for the Very-Large Telescope (VLT) is one such case. We present a method capable of lowering the average computational effort (i.e. lowering the average frame-rate) and deliver the same performance figures. It consists of applying a distributed set of update rates to outperform the conventional vector-matrix multiplies (VMM) used for modal reconstruction and control in AO systems when Zernike polynomials or Karhunen-Loeve modes are used as basis. We analyse the low and high-noise regimes for which we outline the theoretical key points and present both semi-analytical and Monte-Carlo simulation results having the Planet-Finder (PF) as baseline system.
In this article we summarize the parameter space exploration for several adaptive optics systems for a 42-m
European Extremely Large Telescope. These systems are modular, and based on a various number of identical
high order wavefront sensor. We explore a single natural guide star single conjugate AO and multi-laser guide
star systems: ground-layer AO, laser-tomography AO, and multi-conjugate AO. The performance estimates are
given in terms of Strehl ratio or, for the GLAO system in terms of ensquared energy.
Simulations of various GLAO systems for telescopes up to 32 meter are presented. We have generated point spread functions of several GLAO configurations using ESO's parallel simulation tool and compared the results with analytically computed PSFs. A good agreement is observed when simulating bright guide stars (both LGSs and NGSs) although the analytical approach does not consider for instance wavefront sensor errors or servo lag. Other more realistic configurations (asymmetrically located and dim guide stars) are investigated and the need for advanced control methods in such cases are considered.
In this paper, we summarize the analysis made on various Adaptive
Optics (AO) modes (including Shack-Hartmann (SH) and Pyramid Wavefront Sensors (PWS)) for the OverWhelmingly Large telescope (OWL). We will show some early results of the performance to be expected with a first generation AO system, working in the infrared.
Several telescope diameters were considered to see the variations as a
function of telescope diameter. This is also compatible with the
concept of "grow a telescope" where the telescope diameter of OWL
grows from 60m to 100m as a function of time.
In a first phase, to simplify the problem, the effects of the central
obstruction were neglected. However, for the Shack-Hartmann (SH)
simulations, additional simulations were carried out with a simulated
OWL pupil, including segmentation errors.
We show some early results for a ground-layer correction system, working with three natural guide stars (NGSs) and a single deformable mirror (DM). An MCAO system based on 2 DMs, 3 NGSs is also investigated. For the last two systems, our results are found to be in
very good agreement with Cibola, an analytical AO modeling tool. We show that some outer scale of turbulence effects improve slightly the
correction quality when going from a telescope diameter of 10m to
100m.
In this paper, we present the simulation tools which have been
developed at ESO to simulate adaptive optics for extremely large
telescopes, and in particular OWL. These tools are based on dedicated
hardware (a cluster of PCs) and dedicated software, written in C, and
which is parallelized.
We present here some details on the hardware itself, and also how the
simulation software has been parallelized.
End-to-End simulations of high strehl Adaptive Optics systems based on Shack-Hartmann and Pyramid wave-front sensors are presented. We limit our study to high temporal bandwidth, in order to focus on the problem of aliasing and detection noise propagation. In particular the effect of spatial filtering is investigated. Some particular features concerning both sensors are highlighted. We analyze the results in terms of residual phase power spectrum.
We made complete end-to-end adaptive optics (AO) simulations to model
the closed loop performance with and without pupil apodization, a
spatially filtered wavefront sensor (SF-WFS) and a coronagraph. We
investigated the SF performance (the Strehl ratio and the stellar
intensity reduction in the halo) with several configurations in
different seeing conditions. We also ran several extensive coronagraph
simulations modeling a 32m telescope to obtain an investigate the
exoplanet detection possibilities. The results show that a
four-quadrant phase mask coronagraph can damp the intensity about
105 times from the original intensity at seeing conditions having r0=20 cm at 0.5μm. When the SF is used, an additional intensity reduction of about 50-70% can be obtained.
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