In this paper, the adaptive optics (AO) system at Keck Observatory is characterized. The AO system is described in detail. The physical parameters of the lenslets, CCD and deformable mirror, the calibration procedures and the signal processing algorithms are exlained. Results of sky performance tests are presented: the AO system is shown to deliver images with an average Strehl ratio of up to 0.37 at 1.59 μm using a bright guide star. An error budget that is consistent with the observed image quality is presented.

Science commissioning of the UnISIS adaptive optics system is underway. In addition to showing test images from this effort, two other topics are discussed. These include a progress report on our continuing effort to improve the UV throughput of the UnISIS laser guide star projection and detection system and our effort to migrate the closed-loop computation engine from OS/2 to real time Linux. The two new improvements to the UV throughput of the laser guide star system involve new high-throughput prisms for the Pockels cell switch and a plan to increase the projected laser energy using anamorphic magnification in the laser beam as it emerges from the Excimer laser.

The adaptive optics system of the 6.5m MMT with its deformable secondary has seen first light on the sky in November 2002. Since then, it has logged over 30 nights at the telescope and has been used with several scientific cameras and a dedicated IR infrared camera. Results so far are extremely encouraging with Strehls of up to 20% in H-band and 98% in M limited in part by the control algorithm that is being improved. Reliability of the deformable secondary mirror (DM) has been remarkable with only one occurrence of a malfunction that required removing the secondary from its hub. In this paper, we review the milestones achieved and the performances obtained in the first year of operation. We will also address the operational constraints associated with the deformable secondary and the steps taken to relax these constraints. We show that despite its apparent complexity, an adaptive secondary AO system can be operated with modest effort from the telescope and AO staff.

The adaptive secondary for the MMT is the first mirror of its kind. It was designed to allow the application of wavefront corrections (including tip-tilt) directly at the secondary mirror location. Among the advantages of such a choice for adaptive optics operation are higher throughput, lower emissivity, and simpler optical setup. Furthermore, this specific implementation provides capabilities that are not found in most correctors including internal position feedback, large stroke (to allow chopping) and provision for absolute position calibration. The mirror has now been used at the MMT during several runs where it has performed reliably. In this paper we discuss the mirror operation and AO performance achieved during these runs in which the adaptive secondary has been operating in conjunction with a Shack-Hartmann wavefront sensor as part of the MMT adaptive optics system. In particular we mention a residual mirror position error due to wind buffeting and other errors of ≈ 15 nm rms surface and a stable closed loop operation with a 0dB point of the error transfer function in the range 20-30 Hz limited mainly by the wavefront sensor maximum frame rate. Because of the location of the adaptive secondary with respect to the wavefront sensor camera, reimaging optics are required in order to perform the optical interaction matrix measurements needed to run the AO loop. This optical setup has been used in the lab but not replicated at the telescope so far. We will discuss the effects of the lack of such an internal calibration on the AO loop performances and a possible alternative to the lab calibration technique that uses directly light from sky objects.

We report on the results of experiments that demonstrate a robust control system for a general-purpose adaptive optics system and provide robust stability analysis for such a system. Using a commercially available high-speed CCD camera in the Shack-Hartmann wavefront sensor and a 37-actuator Xinetics deformable mirror, we are able to achieve closed-loop performance sufficient for many astronomical, vision science, or laser communications applications. The control system must be robust for the various applications and the entire system must be easily set-up, calibrated, and run by a minimally-trained operator. An H-infinity controller, which optimizes the closed-loop stability of a system, is implemented and analyzed.

The pyramid wavefront sensor detects wavefront aberrations by subdividing the complex field at the origin of the focal plane into quadrants. This paper investigates wavefront sensors, such as the pyramid sensor, that subdivide the complex field at the origin of the focal plane into N equal segments. This can be physically realized with either an N-sided prism or by a lenslet array in the focal plane. An alternative reconstruction technique for the pyramid is also proposed to increase the performance of the sensor.

Nowadays many groups in the world are developing adaptive optics (AO) systems for the real time correction of the aberrations introduced by the turbolence of the atmosphere in the field of view of the astronomical telescopes. The Shack-Hartmann wavefront sensor has been often used for the detection of the optical aberrations but over the past few years an alternative wavefront sensor with pyramidic shape has being developed. The properties of this sensor have been extensively investigated both theoretically and experimentally (for example in the AO module of the Italian “Telescopio Nazionale Galileo”). Important features of this pyramidal sensor are that it offers the advantage of either variable gain against the wavefront deformation and tunable sampling of the telescope pupil. These features translate into a considerable gain in the limiting magnitude of the reference star when compared to the classical Shack-Hartmann sensor. The manufacturing of single pyramid prototypes has been initially accomplished using the classical figuring and polishing technique, a time consuming procedure. Since the multi-conjugated adaptive optics (MCAO) that are under study, foresee the use of a large number of identical pyramids, it has been investigated and developed an alternative method for the mass production of this optical component. Using a lithography-dedicated beamline already operating at the ELETTRA Synchrotron in Trieste, a manufacturing technique has been implemented that uses a process named LIGA [Lithography, electroplating (German: Galvanik) and molding (German: Abformung)]. With this method is it possible to create a master pyramid made of a polymeric material and having the characteristics requested. The master is then used to create a metallic mold by means of electroforming. In the end the mold is used for the molding of a number of identical pyramids made in a suitable amorphous optical polymer, using the technique of the hot embossing. This technique produce identical copies of the master pyramid, a desirable feature for the MCAO systems, and once the mold has been manufactured, permit a very fast production of large numbers of identical pyramids. In this paper we present the results obtained with this manufacturing process.

This paper presents a study of the Mach-Zehnder interferometer for the segmentation error measurement in a giant segmented telescope. We present a thorough theoretical anlaysis of the system performance and deliver an analytical formula for the interferometric signal in the Fraunhofer diffraction approximation. We consider the effects which cause system performance degradation, such as gaps and segment edge misfigure. Taking into account photon noise, we determine the limiting star magnitude. A special emphasis is placed on the analysis of system performance in the presence of atmospheric turbulence.

All the projects of the Extremely Large Telescopes (ELTs) are based on segmented primary mirrors. This idea, solving the problem of producing single mirrors having diameter larger than 8m, introduces the needs for an accurate co-phasing of the various segments. The paper presents some laboratory measurements aimed to investigate the use of the pyramid sensor as co-phasing sensor. The pyramid sensor behavior in measuring a differential piston of the incoming wavefront is analyzed in lab using interferometric measurements as reference. The obtained results show that the sensor can measure the differential piston with an accuracy better than 16nm on the whole measurement range 0-2π. Finally the sensor sensitivity i.e. the ratio between sensor signal and differential piston amplitude as a function of the tilt modulation is measured. Using the measured sensitivity values we estimate that the residual differential piston wavefront error due to pure photon noise, considering 2m² area segments and a 15 R mag star is 7.4nm.

The adaptive optics system for the 6.5 m MMT, based on a deformable secondary mirror, has been on the sky now for three commissioning runs totalling approximately 30 nights. The mirror has begun to demonstrate uniquely clean point-spread functions, high photon efficiency, and very low background in the thermal infrared. In this paper we review the lessons learned from the first few months of operation. Broadly, the hardware works well, and we are learning how procedures related to operation, system error recovery, and safety should be implemented in software. Experience with the MMT system is now guiding the design of the second and third adaptive secondaries, being built for the Large Binocular Telescope. In this context, we discuss the general requirements for retrofitting an adaptive secondary to an existing large telescope. Finally, we describe how the new technology can support the design of adaptive optics for 30-cm class telescopes, with particular attention to ground-layer adaptive optics (GLAO), where conjugation as close as possible to the turbulence is important.

Typical adaptive optics systems require a deformable mirror to provide high spatial frequency wavefront correction and a separate tip-tilt mirror so that the deformable mirror’s dynamic range is not exhausted on low order aberrations. Having two correction devices requires additional optical relays to be incorporated in the system, which in turn translates into more cost, size and complexity. If the two devices were combined into an integrated wavefront corrector (IWC), the cost, size and complexity of an adaptive optics system could be drastically reduced. This paper outlines the design and operation of an electro-ceramic driven tip tilt stage that has been designed specifically for a 37 channel deformable mirror. The tip tilt system can deliver more than 500 μradians of tilt, 20 microns of piston, and has natural frequencies greater than 400 hertz. The tip-tilt stage has a fast response time and the axis of rotation is centered at the optical surface. This prevents translation and wavefront shear associated with typical tip-tilt mirrors for which the axis of rotation is centered behind the surface of the mirror. The 37 channel deformable mirror has a 7mm actuator spacing and is designed with high temperature and low outgassing materials which are compatible with high temperature coatings. The IWC may be retrofitted with Xinetics actuators to operate at cryogenic temperatures. We also describe the use of this device in a closed loop adaptive optics system and outline its benefits.

The purpose of this study was the experimental determination of the type of wave aberration corrected by the micro-machined continuous-membrane deformable mirror from OKO Technologies, and the determination of the limitation in the dynamic range of its correction. We wanted to compare these characteristics with the requirements met in vision science and we wanted to be able to judge the capacity and performance of this deformable mirror for this field of application. To characterize the quality of the static aberration correction of the system, we used phase plates simulating astigmatism and higher order aberrations for an artificial eye consisting of a lens and an USAF resolution target. The pupil size used for the scanning area was 6 mm. The adaptive optics system worked as a closed-loop. Our methodology consisted of measuring the aberrations of these plates and subsequently comparing them with the exact specification given by the manufacturer. In a second time, we corrected the wave front and analyze the quality of the correction by comparing the total root mean square wave front error and the Strehl ratio before and after compensation. We also studied the speed of convergence of the system. We then compared the experimental results with the theoretical simulations of the mirror behavior from other publications.

Adaptive optics (AO), a mature technology developed for astronomy to compensate for the effects of atmospheric turbulence, can also be used to correct the aberrations of the eye. The classic phoropter is used by ophthalmologists and optometrists to estimate and correct the lower-order aberrations of the eye, defocus and astigmatism, in order to derive a vision correction prescription for their patients. An adaptive optics phoropter measures and corrects the aberrations in the human eye using adaptive optics techniques, which are capable of dealing with both the standard low-order aberrations and higher-order aberrations, including coma and spherical aberration. High-order aberrations have been shown to degrade visual performance for clinical subjects in initial investigations. An adaptive optics phoropter has been designed and constructed based on a Shack-Hartmann sensor to measure the aberrations of the eye, and a liquid crystal spatial light modulator to compensate for them. This system should produce near diffraction-limited optical image quality at the retina, which will enable investigation of the psychophysical limits of human vision. This paper describes the characterization and operation of the AO phoropter with results from human subject testing.

To obtain full sky coverage, astronomical adaptive optics systems require Na Sodium Beacons (SBs) (also referred to as Laser Guide Stars or LGSs) located at heights extending from 85 to 100 km. When viewed at the edge of large telescopes these SBs appear elongated. For the Euro50 50 meter aperture telescopes this elongation amounts to 6 to 9 arcseconds when the laser is launched from a point on the telescope axis. This is substantially larger than the ~0.6 arcsec FWHM SB when viewed near the telescope center. This so-called "perspective elongation" substantially decreases the sensitivity of SB aided adaptive optics. We describe a way of removing this elongation when using pulsed lasers. It uses rapid (microsecond) refocusing of the telescope with the aid of birefringent lenses and polarization modulators. We present an outline of the SB wavefront sensor for the Euro50.

The LBT Adaptive first light is foreseen for summer 2004. The first light AO system will be part of the Acquisition Guiding and Wavefront sensor unit (AGW) placed at the front bent Gregorian Foci of the telescope. The development and construction of the AO system is an undergoing process at Arcetri Observatory. The main features of the system are: the use of an adaptive secondary mirror with 672 actuators, the adoption of a pyramid wavefront sensor with a maximum sampling of 30x30 subaperture and the use of a small (400x320mm) movable wavefront sensor unit for reference star acquisition. After a brief description of the system the paper report about the progresses made in the design, realization and lab testing of the various parts of the AO system. In particular we describe the new beams configuration for the wavefront sensor board, the lab prototype of the sensor opto-mechanics, the sensor fast camera and its controller, the glass pyramid, the AO system real time and control software.

The two 911mm-diameter adaptive secondary (AS) mirrors for the Large Binocular telescope (LBT) are currently under construction. The design of the units has been based on the extensive experience made on the MMT adaptive secondary mirror during laboratory tests and telescope runs. Mechanics, electronics and control logic have been revised to improve performances and reliability. Each unit has 672 electro-magnetic force actuators. They control the figure of the Gregorian secondary 1.6mm-thick mirrors with an internal loop using the signal of co-located capacitive sensors. The improvement in the computational power of the on-board control electronics allows to use it as real-time computer for wavefront reconstruction. We present the progress of the final unit construction and the preliminary laboratory results obtained with a 45-actuator sub-system used to test the new features introduced in the electronics and mechanics of LBT adaptive secondary mirrors.

The sky coverage and the Strehl Ratio (SR) uniformity over Field of Views (FoV) of some arcmin are two key points for the development of Natural Guide Star (NGS) based Multi-Conjugate Adaptive Optics (MCAO) systems. We developed a numerical code able to simulate the behavior and to evaluate the performance of MCAO Layer-Oriented systems. In this paper we study the two issues and present the results of the simulations. In particular we consider the Multiple Field of View (MFoV) version of the Layer-Oriented concept. This technique allows looking for the reference stars in sky-areas bigger than the FoV corrected by the adaptive system, with a considerable gain in term of sky coverage. In the MFoV approach of the Layer-Oriented the NGS are selected in two or more concentric annular FoVs. In the configuration we take into account the guide stars are chosen in two different FoVs. The references for the ground layer loop are chosen in an annular FoV which inner diameter has the dimension of the scientific one. This annulus has only technical purposes and only a ground layer correction is applied in those sky directions. The reference stars for the highest loop are selected, as usual, in the corrected FoV. First we take into account the sky coverage considering different galactic latitude cases and studying the results distribution of the simulated cases. In order to enable a statistical approach to the problem we considered a big number of NGS configurations for each galactic latitude case considered. Then we take into account the level of SR uniformity in the cases where a useful correction is achieved. We define a function to quantify the SR uniformity over the FoV and we study its distribution using the results computed by the numerical simulations.

We are currently working on four projects employing Multi Conjugate Adaptive Optics in a Layer-Oriented fashion. These ranges from experimental validations, to demonstration facility or full instrument to be offered to an astronomical community and involves telescopes in the range of 4m to 24m equivalent telescope aperture. The current status of these projects along with their brief description is here given.

Current plans for Extreme Adaptive Optics systems place challenging requirements on wave-front control. This paper focuses on control system dynamics, wave-front sensing and wave-front correction device characteristics. It may be necessary to run an ExAO system after a slower, low-order AO system. Running two independent systems can result in very good temporal performance, provided specific design constraints are followed. The spatially-filtered wave-front sensor, which prevents aliasing and improves PSF sensitivity, is summarized. Different models of continuous and segmented deformable mirrors are studied. In a noise-free case, a piston-tip-tilt segmented MEMS device can achieve nearly equivalent performance to a continuous-sheet DM in compensating for a static phase aberration with use of spatial filtering.

A scalable sparse minimum-variance open-loop wavefront reconstructor for extreme adaptive optics (ExAO) systems is presented. The reconstructor is based on Ellerbroek's sparse approximation of the wavefront inverse covariance matrix. The baseline of the numerical approach is an iterative conjugate gradient (CG) algorithm reconstructing a spatially sampled wavefront at N grid points on a computational domain of size equal to the telescope primary mirror diameter D, using a multigrid (MG) accelarator to efficiently speed up convergence and enhance its robustness. The combined MGCG scheme is order N, and requires only 2 conjugate gradient iterations to converge to the asymptotic average Strehl ratio (SR) and root mean squared (RMS) reconstruction error. Average SR and RMS reconstruction error comparison with figures obtained from a previously proposed MGCG FFT-based minimum-variance reconstructor incorporating the exact wavefront inverse covariance matrix on a computational domain of size equal to 2D, indicates relative deviations below 1-2% at realistic measurement noise levels below π/2 rad RMS phase difference. A cost comparison between the sparse MGCG algorithm and a symmetric approximate minimum degree (SYMAMD) preordered Cholesky factorization, indicates that this last method is competitive for real-time ExAO wavefront reconstruction for systems with up to N ≈ 10⁴ since the update rate of the Cholesky factor is typically several orders of magnitude lower than the temporal sampling rate.

The multi-conjugate adaptive optics (MCAO) systems proposed for future giant telescopes will require new, computationally efficient, concepts for wavefront reconstruction due to their very large number of deformable mirror (DM) actuators and wavefront sensor (WFS) measurements. Preliminary versions of such reconstruction algorithms have recently been developed, and simulations of MCAO systems with 9000 or more DM actuators and 33000 or more WFS measurements are now possible using a single desktop computer. However, the results obtained to date are limited to the case of open-loop wavefront reconstruction, and more work is needed to develop computationally efficient reconstructors for the more realistic case of a closed-loop MCAO system that iteratively measures and corrects time-varying wavefront distortions. In this paper, we describe and investigate two reconstruction concepts for this application. The first approach assumes that knowledge of the DM actuator command vector and the DM-to-WFS influence matrix may be used to convert a closed-loop WFS measurement into an accurate estimate of the corresponding open-loop measurement, so that a standard open-loop wavefront reconstructor may be applied. The second approach is a very coarse (but computationally efficient) approximation to computing the minimum variance wavefront reconstructor for the residual wavefront errors in a closed-loop AO system. Sample simulation results are presented for both concepts with natural guide star (NGS) AO and laser guide star (LGS) MCAO systems on 8- and 32-meter class telescopes. The first approach yields a stable control loop with closed-loop performance comparable to the open-loop estimation accuracy of the classical minimum variance reconstructor. The second approach is unstable when implemented in a type I servo system.

Advances in adaptive optics (AO) systems are necessary to achieve optical performance that is suitable for future extremely large telescopes (ELTs). Accurate simulation of system performance during the design process is essential. We detail the current implementation and near-term development plans for a coarse-grain parallel code for simulations of multiconjugate adaptive optics (MCAO). Included is a summary of the simulation’s computationally intensive mathematical subroutines and the associated scaling laws that quantify the size of the computational burden as a function of the simulation parameters. The current state of three different approaches to parallelizing the original serial code is outlined, and the timing results of all three approaches are demonstrated. The first approach, coarse-grained parallelization of the atmospheric propagations, divides the tasks of propagating wavefronts through the atmosphere among a group of processors. The second method of parallelization, fine-grained parallelization of the individual wavefront propagations, is then introduced. Finally, a technique for computing the wavefront reconstructions is analyzed. A parallel version of the block-symmetric Gauss-Seidel smoother, used in the conjugate-gradients reconstructor with multigrid-solver preconditioning, has been implemented. The timing results demonstrate that this is currently the fastest known full-featured, operational multiconjugate adaptive optics simulation.

Adaptive optics will play a crucial role in achieving the full potential of the next generation of large diameter telescopes. In this paper, we present an optical design for a multi-conjugate adaptive optics system for the Giant Magellan Telescope, a 25.7 m telescope with a primary mirror consisting of seven 8.4 m segments. The tri-conjugate MCAO optics is based on adaptive secondary technology developed for the MMT telescope and incorporates dynamic refocus optics for the laser guide star wavefront sensors. We use the results of analytic (non-Monte-Carlo) numerical simulations to determine the optimal configuration of deformable mirrors as well as laser and natural guide stars. The simulation results are extended to include and quantify the effects of wavefront sensor and control loop delay noise as well as dynamic refocus and fitting error on the expected system performance and sky coverage.

Simulation results of a long-baseline optical interferometer with adaptive optics are presented in this paper. Long-baseline optical interferometers have become useful tools for obtaining detailed stellar information and high-resolution images in the astronomy community. Several interferometric systems have been implemented successfully without adaptive optics; however, adaptive optical systems may be needed for a new generation of long-baseline interferometers with large telescopes such as those being developed for the Magdalena Ridge Observatory (MRO). A long-baseline optical interferometer in the turbulent atmosphere is modeled first, then an optical interferometer with an adaptive optics system (AOS) is modeled and the resulting fringe patterns for different input turbulence scales are interpreted. Finally, the performance of a long baseline optical interferometer with and without an AOS is carefully evaluated and recommendations are made for the implementation of adaptive optics in the 1.5-meter MRO telescopes.

In this paper, we describe the progress of the construction of the Multi-Conjugate Adaptive Optics laboratory test-bed at the University of Victoria, Canada. The test-bench will be used to support research in the performance of multi-conjugate adaptive optics, turbulence simulators, laser guide stars and miniaturizing adaptive optics. The main components of the test-bed include two micro-machined deformable mirrors, a tip-tilt mirror, four wavefront sensors, a source simulator, a dual-layer turbulence simulator, as well as computational and control hardware. The paper describes changes in the opto-mechanical design, characteristics of the hot-air turbulence generator, performance achievements with the tip-tilt and MEMS deformable mirrors as well as the design and performance of the wavefront sensors and control software.

We describe the initial results of a laboratory experiment designed to emulate the performance of a multiconjugate adaptive optics (MCAO) system based on dual layer turbulence and dual layer correction.

The Princeton University Terrestrial Planet Finder (TPF) has been working on a novel method for direct imaging of extra solar planets using a shaped-pupil coronagraph. The entrance pupil of the coronagraph is optimized to have a point spread function (PSF) that provides the suppression level needed at the angular separation required for detection of extra solar planets. When integration time is to be minimized, the photon count at the planet location in the image plane is a Poisson distributed random process. The ultimate limitation of these high-dynamic-range imaging systems comes from scattering due to imperfections in the optical surfaces of the collecting system. The first step in correcting the wavefront errors is the estimation of the phase aberrations. The phase aberration caused by these imperfections is assumed to be a sum of two-dimensional sinusoidal functions. Its parameters are estimated using a global search with a genetic algorithm and a local optimization with the BFGS quasi-Newton method with a mixed quadratic and cubic line search procedure.

The Princeton University Terrestrial Planet Finder (TPF) group has been working on a novel method for direct imaging of extra solar planets using a shaped-pupil coronagraph. The entrance pupil of the coronagraph is optimized to have a point spread function (PSF) that provides the suppression level needed at the angular separation required for detection of extra solar planets. When integration time is to be minimized, the photon count at the planet location in the image plane is a Poisson distributed random process. The ultimate limitation of these high-dynamic-range imaging systems comes from scattering due to imperfections in the optical surfaces of the collecting system. The first step in correcting the wavefront errors is the estimation of the phase aberrations. The phase aberration caused by these imperfections is assumed to be a sum of two-dimensional sinusoidal functions. Assuming one uses a deformable mirror to correct these aberrations, we propose an algorithm that optimally decreases the scattering level in specified localized areas in the image plane independent of the choice of influence function of the deformable mirror.

We are developing an ultra high precision Soft X-ray telescope. The design of the telescope is a normal incident one for 13.5 nm band using Mo/Si multilayers. Two ideas are introduced. One is the optical measurement system in order to monitor the precision of the optics system. The other is the adaptive optics system with a deformable mirror. Using an X ray-optical separation filter, we can always monitor the deformation of the optics by optical light. With this information, we can control the deformable mirror to compensate the system distortion as a closed loop system. We confirmed that the absolute precision of the wave front sensor was less than 3 nm rms. This is also confirmed that the determination of the image center of each micro lens can be ~1/100 of the pixel size. The precision of the deformable mirror was roughly 5 nm rms. Using the closed loop control the accuracy of the repeatability of the shape of the deformable mirror is less than 2 nm rms. The shape of the primary mirror was an off-axis paraboloide with an effective diameter of 80 mm. This primary mirror was coated by Mo/Si multilayers. The reflectivity of the primary mirror at 13.5 nm was ranging from 30 to 50%. The X ray-optical separation filter was made from Zr with a thickness of ~170 nm. The transmission of the filter for low energy X-ray measured and was roughly 50% at thickness of ~170 nm. The transmission of the filter for low energy X-ray was measured and was roughly 50% at 13.5 nm.

Understanding the behavior of post-correction speckles in adaptive optics systems at very high Strehl ratio is critical to determining the ultimate effectiveness of such systems for companion searches that may eventually allow the study of extrasolar planets. Recent investigations indicate that speckles, to first order in remnant phase left by the AO system, have a strong "anomalous" component that is not included in the standard (1-S) estimates of the power in the focal plane halo. Brightness of individual anomalous speckles can exceed that of "classical" speckles by orders of magnitude, although it is expected that other unusual properties of the anomalous speckles may cause them to average away rapidly in time integrations, or be instantaneously cancelled by suitable observational techniques. For example, the anomalous speckles are also "pinned," or spatially localized, on secondary Airy maxima, causing them to be suppressed on Airy nulls; they also have zero mean over time, as well as distinct symmetry properties that might be exploited. In this paper, I explore in some detail the range of operational parameters over which anomalous speckles are problematic.

The wavefront sensor is the most critical component of an adaptive optics (AO) system. Most astronomical systems use one of a small number of alternatives, notably the Shack-Hartmann or the curvature sensor; these are sensitive to the first and second derivative of the wavefront phase, respectively. In this paper, we explore a novel adaptation of the phase-contrast technique developed for microscopy by Zernike to measure phase directly, and show that it is potentially useful in astronomical adaptive optics, both for closed-loop wavefront sensing and for off-line calibration of the system PSF. The phase-contrast WFS should enjoy an advantage in lower read noise, as well as a natural match to the piston-type deformable mirror actuators commonly in use with most current Shack-Hartmann systems, and favorable error propagation during wavefront reconstruction. It appears that it might be possible to implement versions with the reasonably broad spectral bandwidth desired for astronomical applications, and to integrate them with relatively minor modifications into existing AO system architectures.

This paper describes the current control system of the multi-conjugate adaptive optics (MCAO) test bench system that is being developed at the University of Victoria, BC, Canada. The design and analysis of a control system for an AO system employing a Micro-Electro-Mechanical-System (MEMS) based deformable mirror is presented. The AO system is part of a larger test bed that is a scale version of an 8-meter telescope. This paper focuses on the control of one deformable mirror with a Shack-Hartmann wave front sensor. Diagrams of how all the components work together as a control system are given. A conversion from actuator signal space to Zernike mode coefficients is presented. Analysis shows that this control system is capable of reducing low frequency aberrations. Shortcomings of the system error rejection are discussed. The steady state and step response to tilt simulated on the wave front sensor is shown.

Dynamically refocusing the Rayleigh backscatter of a modestly powered laser beacon is a concept for increasing LGS brightness by 10 times. Dynamic refocus will allow for high photon return from multiple Rayleigh beacons enabling MCAO for wide field correction of the MMT and Magellan telescopes. In a system without dynamic refocus, light from a beacon integrated from 20 to 30km is blurred to a length of 14arcsecs. In a system with dynamic refocus, the bow tie is restored to a spot limited only by atmospheric seeing. The dynamic refocus system has been designed to deliver images with <3/4arcsec of induced aberration. This paper reports on field tests performed on the Mt. Bigelow Observatory 61” telescope, optically configured to appear as an off-axis sub-aperture of the 6.5m MMT. In these tests the Rayleigh backscatter from pulses of a Q-switched doubled Nd:YAG operating at 5kHZ was dynamically refocused. These preliminary tests present an uncorrected 7 by 3arcsec beacon image. The 7arcsec length is a result of using a field stop as the range-gating mechanism and the 3arcsec limit is due to double pass imaging (projecting and imaging) through the atmosphere in less than ideal seeing conditions. Upon correction, this 7x3arcsec image is dynamically refocused to a 3arcsec FWHM diameter spot.

We describe a scale sensitive deconvolution algorithm for interferometric images. An ideal sky model should be able to pick up correlated emission on all scales and of all shapes. Though the problem can be well formulated mathematically, there are two issues: (1) it is computationally prohibitive, and (2) the choice of an appropriate basis to represent the image is not clear. The work presented here is an interim step towards developing a fully scale sensitive deconvolution algorithm which is computationally efficient as well. This approach, though restrictive as compared to the most general model for the sky, is an enormous improvement over other scale insensitive algorithms and forms the logical limit of multi-resolution CLEAN approach. The sky image is represented using parameterized basis functions with finite support and the algorithm solves for these parameters. The computational load in this approach is reduced by working with an analytical approximation of the Point Spread Function.

Traditional coronagraph design is reviewed and extended to the case of arbitrary pupil geometries with adaptive optics (AO). By selecting a desired focal plane occulting mask and specifying the expected Strehl ratio achieved by the AO system, the design for a matched Lyot stop is given. The outline of the optimum Lyot stop is derived using general considerations of the residual halo from an on-axis source, as well as by maximizing the signal-to-noise ratio. A continuous transmission variant of the optimum Lyot stop is also found by means of a heuristic argument. It is suggested that essentially the same result may be found using a matched-filter analog from signal processing theory. The resulting Lyot stops for multi-segment telescope apertures can be quite unexpected, and a case with six circular segments is considered as an example.

Observations have been made at the Steward Observatory 1.55 m telescope of a four-star asterism in the constellation Serpens Cauda, using a Shack-Hartmann wavefront sensor. The stars are all within a 2 arcminute field, and range in apparent brightness from m_v of 9.4 to 10.6. The instrument placed a 5 x 5 array of square subapertures across the pupil of the telescope, and had sufficient field of view to allow wavefront data to be recorded from all four stars simultaneously. Snapshots at 1/30 s exposure time were recorded, with no temporal coherence between exposures. We have reconstructed the first 20 Zernike modes from the slope data for each star. In a preliminary analysis, we show that the wavefront aberration in each star can be roughly halved by subtracting the average of the wavefronts from the other three stars. The averages represent estimates of the aberration introduced by the lowest few hundred meters of the atmosphere, so the result provides an early indication of the potential for image sharpening by compensation of boundary layer turbulence.