A new adaptive optics system has been constructed for moderately high resolution in the near infrared at the Multiple Mirror Telescope (MMT). The system, called FASTTRAC II, has been designed to combine the highest throughput with the lowest possible background emission by making the adaptive optical element be an existing and necessary part of the telescope, and by eliminating all warm surfaces between the telescope and the science camera's dewar. At present, only natural guide stars are supported, but by the end of 1995, we will add the capability to use a single sodium resonance beacon derived from a laser beam projected nearly coaxially with the telescope. In this paper, we present a description of FASTTRAC II, and show results from its first test run at the telescope in April 1995.

A new interim adaptive system—FASTTRAC IT—has been developed for near-infrared imaging for the Multiple Mirror Telescope (MMT), prior to upgrade to a single 6.5 m mirror. The system employs a real-time adaptive beam combiner consisting of six mirror facets which control the tip and tilt for each of the 1 .8 m primary mirrors. Since the overall piston of the mirrors is not controlled, the light from the six MMT mirrors adds incoherently at the focal plane, producing an image with the diffraction limit of a single mirror but with flux corresponding to a filled 4.5 m aperture. In operational mode the tilts over each of the 1.8 m mirrors will be sampled using a sodium laser guide star. Overall tilt is compensated using a field star imaged in the visible. We present a brief discussion of the various error sources entering into the system performance. Simulations of performance are presented showing the dependence on field star magnitude and angle. the time delay between sense and application of the required correction, and the angle between laser guide star and field position. These simulations demonstrate that FASTTRAC II should readily achieve diffraction limited imaging for a 1.8 m aperture with 6 times the light collection at near-infrared wavelengths.

A sodium-layer laser guide star adaptive optics system has been developed at Lawrence Livermore National Laboratory (LLNL) for use on the 3-meter Shane telescope at Lick Observatory. The system is based on a 127-actuator continuous-surface deformable mirror, a Hartmann wavefront sensor equipped with a fast-framing low-noise CCD camera, and a pulsed solid-state-pumped dye laser tuned to the atomic sodium resonance line at 589 nm. The adaptive optics system has been tested on the Shane telescope using natural reference stars yielding up to a factor of 12 increase in image peak intensity and a factor of 6.5 reduction in image full width at half maximum (FWHM). The results are consistent with theoretical expectations. The laser guide star system has been installed and operated on the Shane telescope yielding a beam with 22 W average power at 589 nm. Based on experimental data, this laser should generate an 8th magnitude guide star at this site, and the integrated laser guide star adaptive optics system should produce images with strehl ratios of 0.4 at 2.2 micrometer in median seeing and 0.7 at 2.2 micrometer in good seeing.

A 50 watt excimer laser (lambda equals 351 nm) has been installed at the Mt. Wilson 2.5- meter telescope in California as part of the UnISIS adaptive optics system. This laser is used to produce Rayleigh guide stars 18 km above Mt. Wilson. In its initial configuration the projection optics are used to create a single laser guide star. The optical system is designed to allow an easy switch to accommodate three laser guide stars if (1) the laser return signal is sufficiently bright and (2) the laser guide star wavefront sensor has a read noise low enough to detect the split signal. The three guide stars are projected simultaneously in a triangular configuration above the telescope pupil. This three laser guide star system design is the first to confront directly the problem of focal anisoplanatism with an array of laser guide stars. The three guide star array provides a test for theoretical analyses of arrays of laser guide stars which will be an inevitable part of the adaptive optics systems of 8-meter and 10-meter class telescopes.

The United Kingdom is funding a program of astronomical adaptive optics (AO), the primary purpose of which is to equip two 4-meter telescopes with common-user (facility) natural guide star AO systems: the 4.2 m William Herschel Telescope on La Palma in the Canary Islands and the 3.8 m United Kingdom Infrared Telescope on Mauna Kea, Hawaii. The program also supports related developments in the following fields: site evaluation (on La Palma and Mauna Kea), IR instrumentation, adaptive secondary mirror design, partial AO, and laser beacons (for La Palma). The structure, purposes, and timescales of the overall program are described. In general, the goal is to deliver AO systems which have wide astronomical application and provide well-optimized performance in a wide range of environmental conditions. The ways in which this goal has conditioned the program are outlined.

We explore the possibilities and limitations of an adaptively corrected dilute-aperture optical telescope. In such a system a non-redundant pupil geometry is coupled with low degree-of- freedom adaptive optics (AO) to achieve a diffraction-limited imaging capability with high fidelity. We show that such a configuration can operate successfully at optical wavelengths where the problems of point-spread-function (PSF) calibration place significant limitations on conventional adaptive optics. A key component of our system is a suite of interferometric wavefront sensors which guarantees that the system operates in a regime where sensitivity to fluctuations in the seeing is reduced. By operating with a sparse pupil, the total number of active components is minimized, as are difficulties associated with implementing the interferometric wavefront sensors. We plan to demonstrate such a system using the University of Durham ELECTRA AO system in the very near future.

The UK Adaptive Optics program is funded to provide common user adaptive optics facilities for UK telescopes. One phase of this program aims to provide an adaptive optical system for the 4.2 m William Herschel Telescope (WHT), sited on La Palma in the Canary Islands. The WHT natural guide star (NGS) adaptive optics system is specified to have optimum correction at 2.2 micrometer in typical to good site seeing conditions. The initial detector system is an infrared camera with a 256 multiplied by 256 InSb array detector. The system will be mounted at the Nasmyth focus on the GHRIL (General High Resolution Imaging Laboratory) optical bench. The AO system optical design currently uses a conventional pupil imaged deformable mirror and an 8 multiplied by 8 Shack Hartmann wavefront sensor (WFS). A CCD camera is intended as the wavefront sensor detector, based on a 64 multiplied by 64 or 80 multiplied by 80 pixel detector array. Modes for turbulent layer conjugation are currently being investigated. It is intended that the system should be a common-user facility. Therefore functions of system configuration, alignment, and operation are being designed to be operated by non-specialists, so that the facility can be used in the same way as one of the standard suite of instruments available for the telescope. This paper describes the current conceptual design of the system.

Scaling laser systems to large sizes for power beaming and other applications can sometimes be simplified by combining a number of smaller lasers. However, to fully utilize this scaling, coherent beam combination is necessary. This requires measuring and controlling each beam's pointing and phase relative to adjacent beams using an adaptive optical system. We have built a sub-scale brass-board to evaluate various methods for beam-combining. It includes a segmented adaptive optic and several different specialized wavefront sensors that are fabricated using diffractive optics methods. We have evaluated a number of different phasing algorithms, including hierarchical and matrix methods, and have demonstrated phasing of several elements. The system is currently extended to a large number of segments to evaluate various scaling methodologies.

The development of modeling algorithms for adaptive optics systems is important for evaluating both performance and design parameters prior to system construction. Two of the most critical subsystems to be modeled are the binary optic design and the adaptive control system. Since these two are intimately related, it is beneficial to model them simultaneously. Optic modeling techniques have some significant limitations. Diffraction effects directly limit the utility of geometrical ray-tracing models, and transform techniques such as the fast Fourier transform can be both cumbersome and memory intensive. We have developed a hybrid system incorporating elements of both ray-tracing and Fourier transform techniques. In this paper we present an analytical model of wavefront propagation through a binary optic lens system developed and implemented at Sandia National Laboratories. This model is unique in that it solves the transfer function for each portion of a diffractive optic analytically. The overall performance is obtained by a linear superposition of each result. The model has been successfully used in the design of a wide range of binary optics, including an adaptive optic for a beam combining system consisting of an array of rectangular mirrors, each controllable in tip/tilt and piston. Wavefront sensing and the control models for a beam combining system have been integrated and used to predict overall systems performance. Applicability of the model for design purposes is demonstrated with several lens designs through a comparison of model predictions with actual adaptive optics results.

We present a novel, high performance, and economical design for tip-tilt mirrors. The two- dimensional tilt of each mirror is sensed through capacitive displacement sensors sensitive to approximately 1 nm rms out to 10 KHz. An analogue PID circuit utilizes this positional feedback to lock the mirrors to the commanded tilt via voice coil drivers. These mirrors achieve a 10 - 90% risetime of 3.0 ms and have a critically damped response at 100 - 150 Hz update rates. We have incorporated six of these tip-tilt mirrors to adaptively combine all six beams from the MMT. During first light of the instrument in April 1995, individual beams improved from 1.1 inch to 0.6 inch FWHM in 60 s exposures corrected with 60 Hz update rates.

Fabrication of electrostatically controlled membrane adaptive mirrors produced with IC- compatible micromachining is reported. Mirrors have rectangular reflective apertures with sizes varied from 1 by 1 mm up to 11 by 11 mm. The surface of the flexible mirror is formed by a free-suspended 0.5 micrometer-thick silicon nitride film coated with a thin reflective layer of aluminum. The rms deviation from plane for a mirror having one square centimeter aperture is 0.2 micrometer, mirrors with optical quality up to lambda/20 may be selected from batch. Up to sixteen mirrors can be fabricated on one four-inch silicon wafer. Optical figure of the reflective membrane is controlled by an array of 1...100 electrostatic actuators of arbitrary shape placed 20...100 micrometer beneath the reflecting membrane. Technology of fabrication is flexible enough to allow for fabrication of varifocal mirrors, multichannel adaptive mirrors, and spatial light modulators. These and some other applications are discussed in the report.

In 1996, the Multiple Mirror Telescope will be replaced with a 6.5 m single primary mirror. Development is currently underway on a sodium laser guide star adaptive optical system for the new telescope. One unique feature will be an adaptive secondary mirror, consisting of 320 individually controlled voice coil actuators on the back side of a thin, 64 cm diameter mirror. This paper describes initial tests on a 15 cm diameter, thin, flat prototype mirror with a single actuator. The thin mirror is held near a thick substrate which also serves as an immovable reference surface. A novel voice coil actuator connects the two glass parts. A custom capacitance sensor surrounding the voice coil actuator measures the absolute distance between the mirror back side and the reference surface. This prototype provides detailed performance measurements, including temporal and spatial actuator response functions. Assembly, alignment, and calibration techniques for the 64 cm mirror will be debugged. The data will help optimize the design and performance of the adaptive secondary.

We describe the development of techniques for the optical fabrication of the adaptive secondary mirror for the 6.5-m MMT Conversion Project. The f/15 secondary is 640 mm in diameter and consists of a 2-mm-thick convex mirror supported on 320 actuators. This mirror will be polished using the stressed lap method and measured using the holographic test plate system developed at the Mirror Lab, but it presents unique challenges because of its flexibility. During fabrication, the support of the thin mirror must be uniform and stiff enough to keep it from bending significantly under polishing forces which are 25 - 50 times the weight of the mirror. We plan to support the thin mirror by attaching it to a rigid glass substrate, and are pursuing two experimental approaches to the attachment: optical contact and blocking with pitch. The experiments are being performed by fabricating 200-mm concave prototypes of the secondary mirror.

A prototype adaptive-optic secondary mirror consisting of a centrally located single fixed voice coil actuator and surrounded by 20 fixed point supports has been characterized optically. A phase-shifting interferometer was used to determine the static influence function and calibrate the capacitive sensor of the prototype secondary. A distance measuring interferometer sampling a single point on the secondary surface at 32 kHz was used to obtain time series data of the dynamic response of the optic. The system impulse response and transfer function were measured directly and the mechanical modes of the structure identified. Measurement philosophy, hardware, and test results are discussed.

The installation and performance characteristics of a 20 W sodium beacon laser system for the 3 m Shane telescope at the Lick Observatory are presented.

The relative wander in the positions of the laser beacons in a multiple beacon system limits the accuracy to which the wavefront can be measured. We describe the design of an experiment to test methods for reducing laser beacon wander. The system employs an excimer laser producing Rayleigh guide stars at an altitude of 10 km mounted at the Coude focus of the Mt. Laguna 1 m telescope. The experimental tests are based on simultaneously creating two guide stars and measuring their apparent differential motion in a set of projection and detection schemes that includes: full aperture broadcast, partial aperture broadcast, full aperture reception, and partial aperture reception.

From natural guide star adaptive optics data taken with the Come-On Plus and with the Starfire Optical Range Generation II instruments in the JHK bands and in the I band respectively, we describe and analyze the point spread function. The ultimate exploitation of adaptive optics images requires the deconvolution and therefore the calibration of the point spread function which is commonly made by observing a point source close to the astronomical target. In the partial correction regime, the calibration mismatch which is the main source of noise or bias in the deconvolution process is induced by the varying seeing conditions. We therefore stress the procedure able to increase the quality of the calibration and discuss the typical performances in terms of astrometry, photometry, and dynamic range to be possibly extracted from current adaptive optics images as a function of the strehl ratio achieved and the stability of the point spread function. Alternative techniques to the point spread function calibration and other problems like anisoplanaticism are briefly reviewed.

The Wavefront Control Experiment (WCE) is a zonal adaptive optics system that has been used to test many different matrix wavefront reconstructors. This has influenced the choice of reconstructors for experiments conducted using the Wavefront Control Experiment at Yerkes Observatory, at the Starfire Optical Range 1.5 m telescope, and the Chicago Adaptive Optics System (ChAOS) at the Apache Point 3.5 m telescope. The matrices are generated from a Macintosh software package, called A⁺, with a graphics user interface. The mathematical basis of many of the reconstructors is outlined, along with our experience using them, and thoughts about future reconstructor concepts.

We describe the proposed real-time reconstructor algorithm and hardware design for the planned 6.5 m MMT monolithic primary upgrade. The real-time reconstructor will use a linear matrix multiply to calculate the command values to be applied to the actuators of an adaptive secondary mirror using input data from a Shack-Hartmann type wavefront sensor which samples the atmospheric turbulence. Each mirror actuator will be controlled by a high- speed inner control-loop which uses capacitive position sensors located at each actuator as feedback. The real-time reconstructor algorithm is designed to take advantage of the presence of this inner control-loop to achieve better overall correction of the atmospheric aberration. The reconstructor design also provides the ability to use wave-front sensor measurements obtained in previous cycles as part of the input vector in the reconstruction algorithm. The real-time reconstructor hardware uses commercially available hardware to implement the reconstruction algorithm at high bandwidths and small latencies.

An experimental method is presented for optimizing the wavefront reconstruction algorithm of a closed-loop adaptive optics system employed with an astronomical telescope. This technique uses wavefront sensor measurements from an independent scoring sensor to calculate adjustments to the reconstruction algorithm which will minimize the residual mean-square phase distortion. The method applies to closed-loop adaptive optics systems incorporating one or more guidestars, a wavefront reconstruction algorithm that is equivalent to a matrix multiply, and one or more deformable mirrors. Simulation results are reported for the case of a hybrid adaptive optics system incorporating one natural guidestar, one laser guidestar, and one deformable mirror. Differences in the spatial resolution of the wavefront sensors for the two guidestars are considered, particularly reduced resolution natural guidestar sensors for use with dim stars.

Experience with the adaptive optics system at the Starfire Optical Range has shown that the point spread function is non-uniform and varies both spatially and temporally as well as being object dependent. Because of this, the application of a standard linear and non-linear deconvolution algorithms make it difficult to deconvolve out the point spread function. In this paper we demonstrate the application of a blind deconvolution algorithm to adaptive optics compensated data where a separate point spread function is not needed.

Adaptive optics systems have been used to compensate for the degrading effects of atmospheric turbulence in images collected with large astronomical telescopes. Post-detection processing techniques are also employed to further improve adaptive optics compensated images. Typically, many short exposure images are collected, recentered to compensate for tilt, and then averaged to overcome randomness in the images and improve signal-to-noise ratio (SNR). Experience shows that some short exposure images in a data set are better than others. The frame selection post-detection processing technique uses an image quality metric to discard low quality frames and improve image spectrum SNR. In this paper, we address key issues pertaining to frame selection performance limits. Theoretical noise tradeoffs are used to establish minimum object brightness for successful application of the frame selection technique. Limits imposed by noise effects result in a minimum object brightness of apparent visual magnitude +8 for point sources and +4 for a typical satellite model imaged with a 1 m diameter telescope with no central obscuration. Effective average point spread functions for point source and extended objects after frame selection processing under equivalent seeing conditions are almost identical. Thus, deconvolution could be applied to images obtained via frame selection.

We use 414 turbulence profiles obtained by scidar over 20 nights to characterize the structure of the nighttime free atmosphere above Mauna Kea, Hawaii and to examine the isoplanatic patch enlargement that can be achieved in adaptive optics by conjugating the deformable mirror (DM) to the seeing layers. It is found that the typical night-time profile is composed of an underlying background of turbulence upon which are often superposed only one or two thin dominant layers. Low level turbulence is weak at the site. The turbulence structure is such that conjugation of a DM to turbulence rather than to the telescope entrance pupil increases the size of the isoplanatic patch by a factor of two (median); much larger gains are occasionally possible. When a single dominant layer is present, which occurs some 60 percent of the time, conjugation of the DM to that thin layer would typically reduce the seeing spread angle by a factor of two over a field of view of many arcmins. These results should be useful in the design and evaluation of AO systems for the site.

A novel form of Shack-Hartmann wavefront sensor is described which can be used in existing infrared and visible cameras with only minimal disturbance to their optics. Such a device has been installed in IRCAM3, the common-user IR camera on UKIRT (United Kingdom Infrared Telescope). The camera's fast readout electronics and a purpose built data storage system allows the wavefront slopes to be measured in 25 sub-apertures at frame rates of between 30 and 100 per second. The first spatially and temporally resolved IR wavefront measurements are presented and an outline is given of the use of this wavefront sensor for long term monitoring on both Mauna Kea, Hawaii and La Palma, Canary Islands.

This paper reports the results of a simulation comparing the performance of the following wavefront sensors when used in a closed loop astronomical adaptive optics (AO) system: a 48- element Shack-Hartmann, a 20-element Shack-Hartmann, and a 20-element curvature sensor. The method chosen for wavefront reconstruction in each case is based on a modal interaction matrix technique with zernike polynomials chosen as the basis modes. No attempt is made to include a real mirror model in the simulation, thus the evaluation of the sensing technique is decoupled from specific mirror technologies. Two different seeing conditions are simulated with various guide star magnitudes. The wavefront distortions are sensed in the visible and the point spread function of the corrected wavefront is recorded in the near infra-red. The effects of photon statistics and various levels of sensor pixel readout noise are also included in the simulations.

The performance of a ground-based optical imaging system is severely degraded from the diffraction limit by the random effects of the atmosphere. Adaptive optics techniques have been used to compensate for atmospheric turbulence effects. A critical component in the adaptive optics system is the wavefront sensor. Presently, two types of sensors are common: the Hartmann-Shack wavefront sensor and the shearing interferometer wavefront sensor. In this paper we make a direct performance comparison of these two sensors. The performance calculations are restricted to common configurations of these two sensors and the fundamental limits imposed by shot noise and atmospheric effects. These two effects encompass the effects of extended reference beacons and sensor subaperture spacings larger than the Fried parameter, r_o. Our results indicate comparable performance for good seeing conditions, and small beacons. However, for poor seeing conditions and extended beacons, the Hartmann sensor has lower error levels than the Shearing interferometer.

A wavefront sensor design is presented. The wavefront sensor will be applied typically to adaptive correction of a ground based astronomical telescope. It comprises a pair of crossed biprisms to act as star image splitters in the telescope image plane, splitting the incident wave into four beams. The biprisms are followed by a lens which forms four pupil images. These exhibit intensity map differences related to the phase gradient of the incident wave, providing that the point spread function overlaps the biprism crossing. This allows standard wavefront reconstruction algorithms to be used to reconstruct the phase map over the aperture. The results from a computer diffraction simulation of this system are presented to show the useful range of the sensor. In addition, a design for an experimental prototype system is presented.

In an adaptive optical system, the effectiveness of wavefront correction is influenced by relative configuration (matching) of the subapertures of the wavefront sensor and actuators of the wavefront corrector. In this paper, the computer simulations for the systems using Hartmann-Shack wavefront sensor, deformable mirror with continuous face plate, and discrete actuators are reported. In the simulation we use the algorithm of direct wavefront slope control. For different configurations of wavefront sensor and wavefront corrector, the wavefront reconstruction matrixes are established based on the measured influence function of deformable mirrors developed in the Institute of Optics and Electronics. The process of wavefront sensing, reconstruction, and correction for different Zernike terms and a series of wavefront induced by Kolmogorov turbulence are simulated. The criteria for evaluating the configurations are residual error of correction and stability of reconstruction matrix (condition number). The results of this investigation show that the configurations in which each subaperture is controlled mainly by three actuators have smaller residual error and better stability. The arrangements of square subaperture with 4 actuators at the corners are unstable and result in a checkerboard pattern of residual wavefront.

The adaptive optics system for the 1.5-m telescope at the Starfire Optical Range, Kirtland AFB, New Mexico has recently been upgraded. Two of the key components in the new system are improved Generation III Shack-Hartmann Wavefront Sensors (WFSs) built by Adaptive Optics Associates (AOA). The performance of the new WFSs has been measured. Measurements indicate a factor of two improvement in noise performance and less inter- subaperture pixel crosstalk resulting in improved closed loop stability. System design and performance measurements are presented.

The performance of an adaptive optical system is strongly dependent upon correctly measuring the wavefront of the arriving light. The most common wavefront measurement techniques used to date are the shearing interferometer and the Shack-Hartmann sensor. Shack-Hartmann sensors rely on the use of lenslet arrays to sample the aperture appropriately. These have traditionally been constructed using MLM or step and repeat technology, and more recently with binary optics technology. Diffractive optics fabrication methodology can be used to remove some of the limitations of the previous technologies and can allow for low-cost production of sophisticated elements. We have investigated several different specialized wavefront sensor configurations using both Shack-Hartmann and shearing interferometer principles. We have taken advantage of the arbitrary nature of these elements to match pupil shapes of detector and telescope aperture and to introduce magnification between the lenslet array and the detector. We have fabricated elements that facilitate matching the sampling to the current atmospheric conditions. The sensors were designed using a far-field diffraction model and a photolithography layout program. They were fabricated using photolithography and RIE etching. Several different designs are presented with some experimental results from a small-scale adaptive optics brass-board.

An adaptive optical system (AOS) with a feedback loop closed via feedforward neural network (NN) is considered. The vector of the wavefront corrector control signals is computed by the network from two vectors of the intensity moments measured in two near-field planes by two matrix photo-detectors. The NN is trained with back-propagation algorithm to predict the vector of AM signals from the measured intensity vectors. During training phase the network forms a control algorithm for a given configuration of the optical system, taking into account misalignments and nonlinearities of the hardware used. A numerical model of a multichannel AOS controlled by a multilayer NN has been built, trained, and run for different low-order input aberrations. The neural control permits a direct conversion of the intensity distribution measured in the near field into control signals of the wavefront corrector. High efficiency of control has been demonstrated for a model of a 16-channel adaptive optical system for arbitrary input aberrations having limited spatial spectrum.

Current interests include the use of adaptive optics systems to image celestial and earth orbiting objects from the ground. Methods, such as the minimum variance reconstructor, have been developed to improve the imaging performance of adaptive optics systems. However, one tool available which has not been fully investigated is the artificial neural network. Neural networks provide nonlinear solutions to adaptive optics problems while offering the possibility to adapt to changing seeing conditions. In this paper we address the use of neural networks for three tasks: (1) to reduce the wave front sensor (WFS) noise variance, (2) to estimate the Fried coherence length, r_o, and (3) to estimate the variance of the WFS noise. All of these tasks are accomplished using only the noisy WFS measurements as input. Where appropriate, we compare to classical statistics based methods to determine if neural networks offer true benefits in performance. We find that neural networks perform well in all three tasks. While a statistics based method is found to perform better than a neural network in reducing WFS noise variance, neural networks perform better than the statistics based methods in estimating r_o and the variance of the WFS noise.

We present an overview of the new adaptive system under development for the conversion of the Multiple Mirror Telescope (MMT) to a 6.5 m continuous primary mirror. The system is optimized for diffraction-limited imaging from 1.6 to 2.2 micrometer wavelength, using an adaptive secondary mirror which directly feeds an infrared science detector at f/15 Cassegrain focus. Nearly full sky coverage will be obtained using a low-power, continuous wave (cw) sodium laser beacon to sense high-order wavefront errors, with image motion sensing using a quadrant detector sensitive to infrared field star photons in the 1.2 - 1.6 micrometer band. Components are currently under development, so that the adaptive instrument can be integrated with the new 6.5 m telescope soon after first light.

Direct detection of planets of neighboring stars by imaging from the ground is extremely challenging, and requires bringing together and extending all that has been learned in the past two decades in adaptive optics experiments and development. From a distance of 30 light years, the planet Jupiter would be 10⁹ times dimmer than the sun, and at 0.5 arcsec separation would be lost in the strong glare of scattered light from the central star. In this paper, we lay out the requirements for adaptive optics to allow direct detection with a large telescope. The stellar halo must be suppressed by several orders of magnitude, and speckle noise caused by correlated wavefront errors must be severely reduced to allow efficient smoothing of the halo through averaging of random fluctuations caused by photon noise. For a 6.5 m telescope imaging near 1 micrometer wavelength, suppression of the stellar halo to 10^-6 of the peak intensity allows direct detection of Jupiter-like planets in several hours of integration. A deformable mirror with approximately 10,000 correction elements is needed, updated at 0.5 millisec intervals using a wavefront sensor optimized for use with bright stellar sources. Local filtering of wavefront sensor data is required to overcome correlated errors arising from time delay between sensing and imaging. Correction of the strongest amplitude errors caused by scintillation allows the required integration times to be decreased by a factor of 2. We present results of detailed simulations for an adaptive system which achieves the above goals, for imaging at 1 micrometer wavelength with a 6.5 meter telescope. A simulated image of a solar system twin at 8 parsecs shows Jupiter at the 5 (sigma) level for a 5 hour integration. We plan to develop and use a similar system to conduct a two- hemisphere survey of bright nearby stars on the twin 6.5 m MMT and Magellan telescopes.

The status and goals of the W. M. Keck Observatory adaptive optics (AO) program are reviewed. The overall system design is discussed, followed by a more detailed presentation of the optical design. Included is a description of a method for focusing the wavefront sensor (WFS) on either natural guide stars (NGS) or laser guide stars (LGS). Also, a combination tilt and focus sensor is described that corrects both the global tilt ambiguity common to LGSs, but also for instability in the focus of the LGS due to changes in the altitude of the sodium layer.

The second Keck ten meter telescope (Keck-II) is slated to have an infrared-optimized adaptive optics system in the 1997 - 1998 time frame. This system will provide diffraction-limited images in the 1 - 3 micron region and the ability to use a diffraction-limited spectroscopy slit. The AO system is currently in the preliminary design phase and considerable analysis has been performed in order to predict its performance under various seeing conditions. In particular we have investigated the point-spread function, energy through a spectroscopy slit, crowded field contrast, object limiting magnitude, field of view, and sky coverage with natural and laser guide stars.

We discuss the nature and general properties of the effect with regard to the imaging through the turbulent atmosphere. This new effect utilizes the medium inhomogeneities as a part of the optical system to obtain the resolution beyond the diffraction limit. Turbulence superresolution effect relates to the focusing properties of the random medium. We discuss some general properties of image distortions by random refractive medium and present the experimental results revealing important statistical connections between global properties of distorted image and superresolution events. We present the results of the postdetection processing of the short- exposure images which is capable to preserve and accumulate information beyond the diffraction limit.

A laser guide star adaptive optics system is being built for the W. M. Keck Observatory's 10- meter Keck II telescope. Two new near infra-red instruments will be used with this system: a high-resolution camera (NIRC 2) and an echelle spectrometer (NIRSPEC). We describe the expected capabilities of these instruments for high-resolution astronomy, using adaptive optics with either a natural star or a sodium-layer laser guide star as a reference. We compare the expected performance of these planned Keck adaptive optics instruments with that predicted for the NICMOS near infra-red camera, which is scheduled to be installed on the Hubble Space Telescope in 1997.

This paper presents experimental results from a study of the performance of a ferroelectric liquid crystal spatial light modulator (FLCSLM) used as an aberration corrector. The FLCSLM, with suitable polarizing optics, acts as a binary phase only modulator. Using a cascaded system of three such FLCSLMs we obtain up to eight discrete levels of phase modulation over an array of 128 by 128 pixels. Partial correction of phase aberration is effected by using the FLCSLMs to provide a discretized approximation to the phase conjugate of the aberrated wavefront. Performance limitations due to phase quantization, spatial quantization, and inter-pixel gap are discussed in terms of achievable Strehl ratios. These experimental and theoretical results, coupled with other considerations we present, support the suggestion that FLCSLMs could play a role in adaptive optical systems for astronomical telescopes.

Simulating the effects of atmospheric turbulence on optical imaging systems is an important aspect of understanding the performance of these systems. Methods exist for making random draws of phase screens which arise from the Kolmogorov spectrum. In this paper we describe and demonstrate a method for creating random draws of phase screens which would arise from the von Karman spectrum. This phase screen generation technique can be used to make random draws of properly correlated stacks of phase screens shifted in time with respect to each other, and to create properly correlated phase screens arriving from different directions at the telescope pupil. In this paper we present the basic theory and implementation of this phase screen generation technique. Phase screen generation and point spread function results are presented.

In January 1994, we began construction of a modern adaptive optics system for the newly refurbished 100-inch telescope. The design philosophy of the adaptive optics system is to achieve a working system in the visible in a short time at relatively low cost. This means wavefront sensing with natural guide stars and implementation at the bent Cassegrain focus of the telescope. The system has an integrated wavefront sensor and finder camera, and is automated for one-person operation. It uses off-the-shelf components where possible. The deformable mirror, which has 241 actuators, is on loan from the U.S. Air Force. The use of an existing mirror imposes constraints that have driven some of the design considerations. The system is operating at the telescope, with early results described below.