The relay mirror concept involves deploying a passive optical station at a high altitude for relaying a beam from a laser weapon to a target. Relay mirrors have been proposed as a method of increasing the range of laser weapons that is less costly than deploying a larger number of laser weapons. Relay mirrors will only be effective if the beam spreading and beam quality degradation induced by atmospheric aberrations and thermal blooming can be mitigated. In this paper we present the first phase of a multi-year effort to develop a theoretical and experimental capability at Boeing-SVS to study these problems. A team from MZA and Boeing-SVS has developed a laboratory test-bed consisting of a distributed atmospheric path simulated by three liquid crystal phase screens, a Shack-Hartmann wavefront sensor, and a MEMS membrane deformable mirror. We present results of AO component calibration and evaluation, the system construction, and the system performance.

Correlation tracking is investigated as a method for reducing fade probability in free-space laser communication (LaserCom) systems. Challenging operating scenarios can lead to spot breakup in the focal plane image. During moments of spot breakup a traditional centroid tracker can force an intensity valley to the on-axis position and cause unnecessary drops in received power. We investigate alternate tracking schemes to specifically prevent the occurrence of this detrimental mode of operation. Correlation tracking is proposed and evaluated as one approach for improving performance in terms of fade probability. From a broader perspective, we also begin to investigate the phenomenology of deep fades. This approach may lead to additional methods to improve performance in situations where fade probability is the metric of interest.

The imaging properties of optical microscopes can be severely compromised by specimen-induced aberrations causing degraded resolution, reduced signal levels, and image distortion. This is particularly the case in high-resolution, three-dimensional techniques, such as scanning confocal or multi-photon fluorescence microscopy - techniques used extensively in the biological sciences. The aberrations are caused by spatial variations of refractive index within the specimen itself. In wide-field microscopes, this gives rise to aberrations that change across the field of view; in scanning microscopes, they cause temporal variations as the focal spot is scanned through the specimen. The application of adaptive optics to this problem has obvious potential and the principle has been demonstrated in scanning microscopes. To characterise the optical properties of specimens and determine the requirements for adaptive microscopes, we have performed the first detailed study of biological specimen-induced aberrations using an interferometer incorporating high NA microscope objectives. We show that low order correction of aberrations produces significant recovery of signal and resolution and we compare the performance of different correction devices, e.g. deformable and segmented mirrors, for imaging such specimens. It is also shown that that the presence of tip, tilt and defocus modes leads to three-dimensional image distortion that is not easily removed by an adaptive correction system.

We present and analyze experimental results of lab-based open-loop turbulence simulation utilizing the Adaptive Aberrating Phase Screen Interface developed by ATK Mission Research, which incorporates a 2-D spatial light modulator manufactured by Boulder Nonlinear Systems. These simulations demonstrate the effectiveness of a SLM to simulate various atmospheric turbulence scenarios in a laboratory setting without altering the optical setup. This effectiveness is shown using several figures of merit including: long-term Strehl ratio, time-dependant mean-tilt analysis, and beam break-up geometry. The scenarios examined here range from relatively weak (D/r_o = 0.167) to quite strong (D/r_o = 10) turbulence effects modeled using a single phase-screen placed at the pupil of a Fourier Transforming lens. While very strong turbulence scenarios result long-term Strehl ratios higher than expected, the SLM provided an accurate simulation of atmospheric effects for conventional phase-screen strengths.

One of the most common and important tasks in wave optics simulation is choosing what mesh spacings and mesh dimensions to use for a given problem. To obtain correct results, it is crucial that the mesh spacings are sufficiently small and the mesh dimensions sufficiently large, but if one makes the spacings too small, or the dimensions too large, that can greatly increase the simulation run time, and that may be unaffordable. It is therefore important to understand exactly what the applicable constraints are, so that one may choose mesh spacings and dimensions that will yield correct results without being over-conservative. However this problem can be nontrivial, especially when modeling propagation through aberrating media, or when there is potentially useful a priori information available which might allow us to relax the modeling constraints. For example, if the light source is known to be well-collimated, we know that all of the light to be modeled will be concentrated along one axis, allowing us to use smaller meshes than we would if the light were uncollimated. Similarly, if the receiver has a limited field of view, we need not model any light incident upon it from angles outside its field of view. In this paper we present a simple general method to determine what mesh spacings and dimensions will work for any given wave optics propagation problem, including problems involving propagation through aberrating media and/or a priori information about the source and/or receiver.

Laser systems are finding a home in many military applications - such as Space Situational Awareness, imaging and weapons systems. With an increasing focus on programs that entail atmospheric propagations, there is a need for a cost effective method of performing laboratory proof-of-concept demonstrations. The use of one SLM (single phase screen) to model atmospheric effects has been investigated previously with promising results. However, some effects cannot be captured with a single SLM. This paper focuses on the addition of a second SLM and quantifying the results. Multiple screens will allow the user to independently control the Fried parameter, the isoplanatic angle, and Rytov Variance. The research is comprised of simulation and experiment. The simulation demonstrates the ability to accurately model atmospheric effects with two phase screens. Based on the simulation, a hardware implementation was tested in the lab. The results of this research show promise, however some issues remain. This thesis describes the experimental set-up and results based on measurement of phase and intensity of the propagated field. It was noted that while analytic results are replicated in simulation, similar results in the lab were difficult to achieve.

A new algorithm of the dislocation localization is suggested. It is based on the analysis of projections field of phase gradients. Accuracy of the algorithm is verified by numerical simulation. Special attention is focused on the precision of singular points (wavefront dislocations) screening. The algorithm is evaluated with respect to others and its advantages and drawbacks are cleared up. The method described can be included in the software of the Hartmann's sensor and be used in the full-scale experiments. Also the original algorithm of phase reconstruction is proposed and its characteristics are estimated. This algorithm requires detection of dislocation coordinates so it should be used together with the algorithm of dislocation localization. In the paper the comparison is performed of the proposed algorithm with the well known Fried's algorithm. After that the phase reconstruction technique is included into the model of a typical adaptive optics system.

Based on the widely used Gullstrand-Le Grand eye model, the individual human eye model has been established here, which has individual corneal data, anterior chamber depth and the eyeball depth. Furthermore the foremost thing is that the wavefront aberration calculated from the individual eye model is equal to the eye's wavefront aberration measured with the Hartmann-shack wavefront sensor. There were four main steps to build the model. Firstly, the corneal topography instrument was used to measure the corneal surfaces and depth. And in order to input cornea into the optical model, high order aspheric surface-Zernike Fringe Sag surface was chosen to fit the corneal surfaces. Secondly, the Hartmann-shack wavefront sensor, which can offer the Zernike polynomials to describe the wavefront aberration, was built to measure the wavefront aberration of the eye. Thirdly, the eye's axial lengths among every part were measured with A-ultrasonic technology. Then the data were input into the optical design software -ZEMAX and the crystalline lens's shapes were optimized with the aberration as the merit function. The individual eye model, which has the same wavefront aberrations with the real eye, is established.

All extended optical systems with aberrations suffer from anisoplanatism effect. In this presentation we investigate anisoplanatism in human eye. For that purpose we use a reference source (beacon) obtained by focusing of a dim laser beam on the retina and consider increasing the retina resolution within anisoplanatic angle by means of ideal wavefront corrector and a real bimorph flexible one. The numerical simulations of isoplanatic patch size of human retina were made for different beacon positions and based on the aberrations measured by means of custom wavefront-guided aberrometer. We found out that in particular human eye the existence of optimal correction directions is possible. As the behavior of Zernike coefficients varies from subject to subject the existence of optimal correction angle is a feature of a particular eye. We also estimated the contribution of low-order and high-order aberrations in anisoplanatism effect for the subjects we measured. We found out that aberrations with strongly variable amplitude across the visual field have effect on the isoplanatic patch size most. In this paper we illustrated the isoplanatic patch enlargement with variation of beacon position by presenting two-dimensional retina and test object images. Also anisoplanatism in two-layer human eye model has been discussed. As the main part of the eye's aberrations is induced by the surfaces of the cornea and the crystal lens, our model consists of two thin phase screens that correspond to the cornea and the lens. Then we used such two-layer model to minimize residual mean-square error of correction by means of just one applied corrector.

In this presentation a dynamic model of human eye based on bimorph flexible mirror is introduced. We demonstrate experimental data of reproducing low- and high-order aberrations typical for human eye with RMS error about 5% and discuss possibility to reproduce their time-tracings.

New applications of adaptive optics, especially in the potentially mass markets such as laser optics, imaging and medicine, require development of new components with high quality and low price. These requirements are equally applicable to wavefront sensors, wavefront reconstructors and wavefront correctors. The whole concept of adaptive optics as a science-intensive technology needs to be altered, to facilitate low-cost and service-free deployment and user-unaware exploitation. As an example of a technology, that has a good low-cost potential, we describe the technology of piezoelectric deformable mirrors with actuators based on the transversal piezoelectric effect, as an inexpensive alternative to the deformable mirrors with stacked actuators.

We present an analytic evaluation of the optical performance of a tip/tilt and piston Spatial Light Modulator, for use in adaptive optic and beam steering applications. The impact of array fill factor, pixel curvature, position and tilt accuracy, and pixel yield are discussed in detail. Two arrangements for beam steering are presented and analyzed; in the first the SLM is used as a programmable higher-order diffraction grating, and in the second the SLM acts as a programmable Fresnel lens inside a telescope.

Electrostatic Membrane Deformable Mirror (MDM) technology developed using silicon bulk micro-machining techniques offers the potential of providing low-cost, compact wavefront control systems for diverse optical system applications. Electrostatic mirror construction using bulk micro-machining allows for custom designs to satisfy wavefront control requirements for most optical systems. An electrostatic MDM consists of a thin membrane, generally with a thin metal or multi-layer high-reflectivity coating, suspended over an actuator pad array that is connected to a high-voltage driver. Voltages applied to the array elements deflect the membrane to provide an optical surface capable of correcting for measured optical aberrations in a given system. Electrostatic membrane DM designs are derived from well-known principles of membrane mechanics and electrostatics, the desired optical wavefront control requirements, and the current limitations of mirror fabrication and actuator drive electronics. MDM performance is strongly dependent on mirror diameter and air damping in meeting desired spatial and temporal frequency requirements. In this paper, we discuss characterization measurements and modeling of MDM spatial and temporal performance for different mirror designs and present application results illustrating the diverse uses of MDM technology in optical wavefront compensation systems.

The compact adaptive optics mirror is described, which allows compensation of wave front distortions related to low-order aberrations such as tip/tilt, focus/defocus, astigmatism, etc. of the laser beam distorted, for example, because of propagation through atmospheric turbulences.

The MEMS Phase Former Kit developed by the Fraunhofer IPMS is a complete Spatial Light Modulator system based on a piston-type Micro Mirror Array (MMA) for the use in high-resolution, high-speed optical phase control. It has been designed for an easy system integration into an user-specific environment to offer a platform for first practical investigations to open up new applications in Adaptive Optics. The key component is a fine segmented 240 x 200 array of 40 μm piston-type mirror elements capable of 400 nm analog deflection for a 2pi phase modulation in the visible. Each mirror can be addressed and deflected independently by means of an integrated CMOS backplane address circuitry at an 8bit height resolution. Full user programmability and control is provided by a newly developed comfortable driver software for Windows XP based PCs supporting both a Graphical User Interface (GUI) for stand-alone operation with pre-defined data patterns as well as an open ActiveX programming interface for a closed-loop operation with real-time data from an external source. An IEEE1394a FireWire interface is used for high-speed data communication with an electronic driving board performing the actual MMA programming and control allowing for an overall frame rate of up to 500 Hz. Successful proof-of-concept demonstrations already have been given for eye aberration correction in ophthalmology, for error compensation of leightweight primary mirrors of future space telescopes and for ultra-short laser pulse shaping. Besides a presentation of the basic device concept and system architecture the paper will give an overview of the obtained results from these applications.

We propose and demonstrate a novel liquid based deformable mirror (LDM). The proposed LDM consists of an array of vertically oriented open capillary channels immersed in a pool of two immiscible liquids. A free-floating thin reflective membrane serves as the reflecting surface. By means of jet action, membrane deformation is induced. The control of jet flow through each channel is achieved by electrostatic means. This individual control enables the generation of complex surface profiles useful for adaptive optics applications. The advantages of this device include high stroke dynamic range, low power dissipation, high number of actuators, fast response time, and reduced fabrication cost. The device, however, can only be operated in a vertical orientation and is suitable for dynamic wavefront correction. A proof of principle of the device using an array of linearly addressed capillary channels is presented. Preliminary measurements showed that the response time is several milliseconds with a stroke of more than 10 microns. The design and fabrication of a prototype with around 100 actuators is in progress.

Characterization and calibration process for a liquid crystal (LC) spatial light modulator (SLM) containing dual frequency liquid crystal is described. Special care was taken when dealing with LC cell gap non-uniformity and defect pixels. The calibration results were fed into a closed loop control algorithm to demonstrate correction of wavefront distortions. The performance characteristics of the device were reported. Substantial improvements were made in speed (bandwidth), resolution, power consumption and system weight/volume.

New devices and approaches are being developed for controlling beam direction and shape using liquid crystal based assemblies. This paper discusses recent advancements in these areas including improvements in zero-order diffraction efficiency, broadband wide field-of-regard steering, wavefront correction using in-line configurations and high average power handling.

We report on work on producing phase-only polymer-dispersed liquid crystals for use in spatial light modulators for adaptive optics. The aim is to assess the magnitude of the achievable phase shifts and the associated slew rate. We describe our methodology of producing devices and present our initial results.

In previous work we demonstrated a nematic liquid crystal MEMS adaptive optics system for observation of low earth orbit satellites. However the closed loop bandwidth was limited to 40 Hz due to latency in the interface electronics between the control computer and the device driver. This bandwidth is marginal for compensation of atmospheric turbulence effects, where the Greenwood frequency is often in excess of 100 Hz. Recently the interface has been redesigned and as a result we have been able to nearly double the bandwidth. In this paper we describe laboratory experiments with the faster system.

Correlation wave-front sensing can improve Adaptive Optics (AO) system performance in two keys areas. For point-source-based AO systems, Correlation is more accurate, more robust to changing conditions and provides lower noise than a centroiding algorithm. Experimental results from the Lick AO system and the SSHCL laser AO system confirm this. For remote imaging, Correlation enables the use of extended objects for wave-front sensing. Results from short horizontal-path experiments will show algorithm properties and requirements.

In this talk we will present a new zonal wavefront sensor. The device consists of a multiplexed hologram which can reconstruct multiple diffracted beams to an image plane with the input of a single object beam. In operation, a wavefront incident on the hologram is divided up into various output beams according to the presence and strength of particular aberrations present in the input. The Zernike terms are then simply read out according to the location of the foci on the image plane CCD. The wavefront information is thus derived without the need for any computations; in effect representing an all-optical, massively parallel processing method with virtually limitless bandwidth. Furthermore, because of the minimal computing electronics required this type of sensor is compact and permits active wavefront sensing for very small imaging devices.

Conventional adaptive optics (AO) systems using gradient wavefront sensors and linear least-squares reconstructors, perform very poorly when light has propagated through strong atmospheric turbulence. This is due to vortices in the wavefront that cannot be reconstructed using the least-squares method. One solution to the problem is to use non-linear reconstructors, however a second solution is to use direct wavefront sensors that circumvent the reconstruction problem. Direct wavefront sensors are simple self-referencing interferometers that directly measure the phase difference between a reference beam and an aberrated one. In this study the viability of a point-diffraction interferometer for a closed-loop atmospheric AO system was tested. A point-diffraction interferometer was built using a modified Mach-Zehnder set-up. The system was used in closed-loop using a ferroelectric SLM to produce the aberrated wave after correction. The SLM was used to emulate a corrective device that corresponded to a square, 12x12, piston-only segmented mirror with a stroke of ±π. Its performance was tested for the case of atmospheric turbulence aberrations. Both uniform intensity, and scintillated cases were looked at. The investigation showed, through simulation and experiment, that the point-diffraction interferometer worked in closed-loop operation in both uniform intensity and scintillated aberrations. Its robustness in the presence of phase discontinuities makes it a promising option for wavefront sensing in strong scintillation.

The Self-Referencing Interferometer Wavefront Sensor (SRI WFS) has been shown to outperform conventional wavefront sensors in strong scintillation environments. Recently, the Starfire Optical Range has developed a prototype SRI to evaluate its performance. This paper discusses the purposes of optically amplifying the reference beam. Specifically, it addresses regions of operation where gain improves signal-to-noise ratio (SNR) values, and thus the SRI WFS performance. Conditions are also addressed when Amplified Spontaneous Emission (ASE) from the optical amplifier degrades the overall signal, resulting in less than acceptable SNR ratios. Laboratory measurements of SRI WFS performance with an optical amplifier are presented.

The Air Force Research Laboratory is developing a Self-Referencing Interferometer (SRI) wavefront sensor (WFS) for applications requiring laser propagation in strong scintillation. This paper compares several phase-shifting techniques that can be used to capture interference patterns and examines their effects on SRI WFS performance. These techniques include temporal, spatial, and spatial-temporal phase shifting. Temporal phase shifting allows for straightforward setup, alignment, and calibration, though its performance is degraded by changes in the atmosphere between measurements. Spatial phase shifting effectively "freezes" the atmosphere, but requires more rigorous camera calibration and alignment. Spatial-temporal phase shifting balances the benefits and challenges of both methods. This paper includes a discussion of the tradeoffs involved in selecting an appropriate phase-shifting approach for a given application. Laboratory results demonstrate the advantages and disadvantages of each technique in evaluation of SRI WFS performance.

The atmospheric turbulence severely limits the resolution of ground based observation systems. Adaptive optics provides a real time compensation of these effects. The correction quality relies on a key component, the Wave Front Sensor (WFS), that analyses the perturbation. When observing extended sources the WFS precision is limited by anisoplanatism effects induced by the distribution of the turbulence in the volume ahead of the instrument. Anisoplanatism induces a variation of the turbulent phase and of the collected flux in the field of view. The apparent evolution of the flux variations is often called differential scintillation. We study the impact of this phase and scintillation anisoplanatism on wavefront sensing. Scintillation anisoplanatism and its coupling with phase effects have to be taken into account. An analytical expression of the error induced on the phase estimate is given in the Rytov regime. The formalism is applied to different cases of observation.

In this paper, we present a novel adaptive optics testbed and its performance evaluation procedures. The testbed was built in the New Mexico State University (NMSU) Electro-optics Research Laboratory (EORL). NMSU's EORL adaptive optics testbed includes a tip-tilt error compensation system and a higher-order phase aberration compensation system. The tip-tilt error compensation was completed using a fast steering mirror with a quadrant cell detector. The higher-order phase aberration compensation was achieved using a 37-actuator deformable mirror and image sharpness with a stochastic parallel gradient descent algorithm (SPGDA). A metric optimization process was added in the SPGDA to fit an 8-bit deformable mirror control card. The system performance is evaluated using both static and dynamic phase aberration test conditions.

Small Micro-Electro-Mechanical Systems (MEMS) deformable mirror (DM) technology is of great interest to the adaptive optics (AO) community. These MEMS-DM's are being considered for many conventional AO applications since they posses some advantages over conventional DM's. The MEMS-DM technology is driven by the expectation of achieving improved performance with lower costs, low electrical power, high number of actuators, high production rates, and large reductions in structural mass and volume. In addition to the imaging community, the directed energy community is also interested in taking advantage of the characteristics which MEMS-DM's offer. Unlike imaging, the optical fill-factor of a high-energy laser DM, has to be essentially 100 percent! Many modern MEMS-DM designs consist of small, lightweight, segmented mirrors that can be precisely controlled. For high-energy laser applications, the MEMS DM's should have a continuous reflective face-sheet with no gaps. This continuous reflective face-sheet must include high-energy laser coatings, which render the face sheet very stiff. This is a new challenge for MEMS-DM's, which has not previously been addressed. The Air Force Research Laboratory has proposed to meet this challenge with several continuous face-sheet high-energy laser MEMS-DM's designs. This paper will give a generic description of a MEMS-DM computer model. The research goal is to develop a MEMS-DM model for closed loop control of a high-energy laser, MEMS-DM adaptive optics application.

In the framework of zonal approach for Multi Conjugate Adaptive Optics (multiple-mirror, multiple-guide star) we investigate a predictive Kalman Filter (KF) based controller and a non-predictive classical Minimum Variance (MV) algorithm. The main goal of this work is to compare phase estimation performance achievable by the computationally more expensive Kalman filter approach, which explicitly accounts for the atmospheric turbulence temporal behavior through a first order autoregressive evolution model, and a simpler MV algorithm with and without temporal prediction. For representative examples of the Palomar 5.1 meter telescope single conjugate and Gemini-South 8 meter telescope multi conjugate adaptive optics systems the performance of KF and MV controllers has been compared with respect to their turbulence estimation capability. We have found that the KF algorithm, showing superior performance for single conjugate adaptive optics systems, is less effective in multi conjugate case. It has also been shown that MV algorithm with a temporal prediction added to it can work nearly as good as KF.

Image metric optimization is an attractive alternative to conventional wavefront sensing for optical systems that are constrained by weight, cost, size, and power consumption and required to operate using light from extended object scenes. For these optical systems, an image metric optimizer must be able to function in the presence of potentially large system aberrations. This paper examines the usefulness of image entropy as a metric for measuring changes in image quality in the presence of large aberrations. In our experiment, we use a liquid-crystal spatial light modulator as a programmable diffractive optic to compensate for roughly 40 waves of peak-to-valley aberration introduced by using a parabolic mirror tilted 5 degrees off the optic axis. The results of our experiment show that image entropy does function well as a metric for measuring changes in image quality for 20 waves of aberration or less. For aberrations greater than 20 waves peak-to-valley the total optical power incident on the camera is a better metric.

The future European Extremely Large Telescope will be composed of one or two giant segmented mirrors (up to 100 m of diameter) and of several large monolithic mirrors (up to 8 m in diameter). To limit the aberrations due to misalignments and defective surface quality it is necessary to have a proper active optics system. This active optics system must include a phasing system to limit the degradation of the PSF due to misphasing of the segmented mirrors. We will present the lastest design and development of the Active Phasing Experiment that will be tested in laboratory and on-sky connected to a VLT at Paranal in Chile. It includes an active segmented mirror, a static piston plate to simulate a secondary segmented mirror and of four phasing wavefront sensors to measure the piston, tip and tilt of the segments and the aberrations of the VLT. The four phasing sensors are the Diffraction Image Phase Sensing Instrument developed by Instituto de Astrofisica de Canarias, the Pyramid Phasing Sensor developed by Arcetri Astrophysical Observatory, the Shack-Hartmann Phasing Sensor developed by the European Southern Observatory and the Zernike Unit for Segment phasing developed by Laboratoire d'Astrophysique de Marseille. A reference measurement of the segmented mirror is made by an internal metrology developed by Fogale Nanotech. The control system of Active Phasing Experiment will perform the phasing of the segments, the guiding of the VLT and the active optics of the VLT. These activities are included in the Framework Programme 6 of the European Union.

Gruneisen has shown that small, light weight, liquid crystal based devices can correct for the optical distortion caused by an imperfect primary mirror in a telescope and has discussed the efficiency of this correction. In this paper we expand on that work and propose a semi- analytical approach for quantifying the efficiency of a liquid crystal based wavefront corrector for this application.

This paper presents an analytic treatment of the wavelength dependences associated modulo λ_r optical path control, treating the case where the reset wavelength λ_r is allowed to be an integer multiple of a nominal operating wavelength λ₀, λ_r=Nλ₀. Equations for the wavelength dependences associated with modulo Nλ₀ optical path modulation are derived using both a Strehl ratio analysis approach and a Fourier analysis approach. Geometrical analysis of the transmitted wavefront yields expressions for the Strehl ratio and angular dispersion that are in agreement with the N^th-order diffraction efficiency and angular dispersion relationships derived by Fourier analysis. The Fourier analysis approach yields additional expressions for the diffraction efficiency and wavefront characteristics associated with all diffracted orders.

OSSim (Optical System Simulation) is a wave-optics, time-domain simulation toolbox with both optical and data processing components developed for adaptive optics (AO) systems. Diffractive wavefront control elements have recently been added that accurately model optically and electrically addressed spatial light modulators as real time holographic (RTH) devices in diffractive wavefront control systems. The developed RTH toolbox has found multiple applications for a variety of Boeing programs in solving problems of AO system analysis and design. Several complex diffractive wavefront control systems have been modeled for compensation of static and dynamic aberrations such as imperfect segmented primary mirrors and atmospheric and boundary layer turbulence. The results of OSSim simulations of RTH wavefront compensation show very good agreement with available experimental data.

This paper builds upon past work demonstrating the integrated performance of a programmable diffractive element of large pixel count with a telescope system. More specifically, a liquid-crystal-based spatial light modulator is used as a reconfigurable diffractive optical element in a telescope system to extend the systems field of regard by compensating large aberrations associated with off-axis orientation of the primary mirror and by steering object light over angles greater than the instantaneous field of view.

Large aperture optical quality primary mirrors have been developed which are extremely lightweight (areal densities less than 1kg/m2) made from stretched reflective polymer membranes. However, aberrations induced by boundary support errors and pressurization of a flat membrane do not produce a perfect parabolic shape. Modeling studies have shown that active boundary control can be very effective in correcting certain types of figure errors typically seen in membrane mirrors. This paper validates these design studies by applying boundary control on a 0.25-meter pressure augmented membrane mirror (PAMM). The 0.25 meter PAMM was fabricated as a pathfinder for a larger prototype. A combination of displacement actuators and electrostatic force actuators were used to control the shape of the mirror. A varied thickness stress coating prescription was developed by a SRS/AFRL team using nonlinear membrane theory. Based on modeled data, the stress coating should force the membrane into a parabolic shape when pressurized, as opposed to a spherically aberrated shape characteristic of a pressurized flat membrane. Test data from the 0.25-meter PAMM proved that the varied thickness stress coating allows for a better shape than the uniform coating.

An innovative adaptive optic is discussed that provides a range of capabilities unavailable with either existing, or newly reported, research devices. It is believed that this device will be inexpensive and uncomplicated to construct and operate, with a large correction range that should dramatically relax the static and dynamic structural tolerances of a telescope. As the areal density of a telescope primary is reduced, the optimal optical figure and the structural stiffness are inherently compromised and this phenomenon will require a responsive, range-enhanced wavefront corrector. In addition to correcting for the aberrations in such innovative primary mirrors, sufficient throw remains to provide non-mechanical steering to dramatically improve the Field of regard. Time dependent changes such as thermal disturbances can also be accommodated. The proposed adaptive optic will overcome some of the issues facing conventional deformable mirrors, as well as current and proposed MEMS-based deformable mirrors and liquid crystal based adaptive optics. Such a device is scalable to meter diameter apertures, eliminates high actuation voltages with minimal power consumption, provides long throw optical path correction, provides polychromatic dispersion free operation, dramatically reduces the effects of adjacent actuator influence, and provides a nearly 100% useful aperture. This article will reveal top-level details of the proposed construction and include portions of a static, dynamic, and residual aberration analysis. This device will enable certain designs previously conceived by visionaries in the optical community.

The first prototype of an actuator for a new adaptive deformable mirror (DM) is presented together with the development of a 61-actuator grid element. The DM design consists of a thin membrane which acts as the correcting element. A grid of low voltage electro-magnetical push-pull actuators, impose out-of-plane displacements in the mirror's membrane. To provide a stable and stiff reference plane for the actuators, a mechanically stable and thermally decoupled honeycomb support structure is added. Several variants of variable reluctance actuators are considered. Each actuator consists of a closed magnetic circuit in which a strong permanent magnet (PM) provides a static magnetic force attracting ferromagnetic material. By applying a current through a coil which is situated around this magnet, this force can be influenced. Depending on the mechanical stiffness of the actuator, this leads to a certain displacement. Both the PM and the coil are connected to the fixed world and only the ferromagnetic material will move. The actuators are produced in arrays which make the design easy and extendable. The power dissipation in the actuator grid is in the order of milliwatts per actuator. Because of this low power dissipation active cooling is not required. The paper describes how the actuator stiffness and efficiency can be controlled. A test-setup is developed in which the actuator characteristics are measured.

Reported is an investigation of a novel approach for producing and correcting active optical mirrors. Photoactive polymers represent a special class of "smart materials" whose electronic and physical properties such as conductivity, charge distribution, and especially shape can be changed in response to the environment (voltage, light, stress). The ability of photoactive polymers to change the structure of a polymer matrix in response to light is being studied to allow active figure control of membranes for optical element use. Photoactive substrates (mirrors) were produced. Incoherent light sources were used to effect shape control. Shack-Hartman Wavefront sensing was used to quantify the initial and optically altered figure of samples. Motion of two classes of samples was measured and is reported here. Proposed is also a new stress control technology as well as new hybrid technology combining two classes of photoactive materials.

The need and desire for large-scale reflectors is immediate and long lasting. Therefore engineers and designers are turning toward processes that produce reflectors much different than the conventional ground glass mirror. This paradigm shift encompasses many new and emerging technologies, including, but not limited to, pressure-augmented stress-coated membrane mirrors. Recent research has centered on determining the proper amount of stress (from the coating) to apply to a membrane substrate to produce a near-net shape that can be augmented with positive pressure to conclude in the smallest figure error. The bulge test has been applied to membrane samples of seven inch diameter, both uncoated and after coating, and central displacements used as data points when coupled with the finite element code ABAQUS to determine strain and stress values. These values are then correlated to the coating process to determine a 'coating prescription' by which that state of minimal figure error can be attained. Vibration testing in vacuum also shows promise as an effective method to determine the amount of stress present in the coated membrane. The shifts in natural frequencies of a coated membrane versus its uncoated self are unique and indicative of the stress increase by the addition of the coating. These natural frequencies are input into theoretical and ABAQUS models to determine strain and stress. This method is used to provide confidence with the bulge test results.

During some years there was a research of properties of an observation telescope with non-ideal primary mirror and non-linear optical correction of received images. Different schemes of reading out of the information about primary mirror distortions were investigated, various types of nonlinear correctors were used, and possible ways of creation of a telescope primary mirror with acceptable optical quality were investigated. Brief history of these researches will be given in this paper. The results of real-time holographic correction of image of a moving object observed by a telescope with a membrane primary 300 mm in a diameter will be also discussed.

A novel wavefront reconstruction algorithm used in the visual science for the wavefront aberration of the human eye with use of the Hartmann-Shack (H-S) sensor is proposed in this paper. We model the gradients of H-S sensor with the Fried geometry. Iterative discrete Fourier transform and the correspondent inverse filter in spatial frequency domain are introduced. The processing of the boundary condition in our algorithm becomes easy and natural, and it is with no necessary to derive the boundary gradients from the measured data. The simulations and experimental results show that the new iterative algorithm can accurately offer the estimated wavefront and gradient data, especially in high precision measurement where the signal-to-noise ratio is high.

The phase front measurements of a vortex laser beam have been carried out with the help of a Shack-Hartmann sensor. The vortex beam is generated in the form of a Laguerre-Gaussian beam (LG₀¹ mode) with the help of the special spiral phase plates manufactured by the kinoform technology. The measured shifts of focal spots on the hartmanogram are compared with the calculated shifts.