Showing papers on "Adaptive optics published in 1982"
TL;DR: The mathematics of the technique are described, some computer simulations which involve both point sources and extended objects are shown and it is shown that the method provides an interesting challenge to designers of optical devices.
Abstract: Wavefront sensing by phase retrieval implies extraction of the Fourier transform of a complex signal based on observation of the modulus of the signal Only the image intensity from a system's focal plane array is required to estimate the phase aberrations These estimates are used to derive control signals to align (or to maintain alignment of) the optical system The concept can be used in both a predetection and postdetection mode In the former, the control system labors to keep the optics in a diffraction-limited mode all the time In the latter, the control system induces a phase or wavelength diversity that allows successive images to be restored to nearly diffraction-limited quality by postprocessing of the image This second mode is particularly interesting because it will reduce the design effort for both the optical system and the control system How the phase or wavelength diversity is achieved is not clear at this time If the method has utility, it provides an interesting challenge to designers of optical devices In this paper we describe the mathematics of the technique and show some computer simulations which involve both point sources and extended objects
639 citations
TL;DR: In this article, the effect of turbulence-induced wavefront distortion for two propagation paths with only slightly different propagation directions can be significantly different, and the implications of this fact for a compensated imaging system and for an adaptive-optics laser transmitter are examined.
Abstract: We examine the consequences for an adaptive-optics system of the fact that the turbulence-induced wave-front distortion for two propagation paths with only slightly different propagation directions can be significantly different. We consider the implications of this fact for a compensated imaging system and for an adaptive-optics laser transmitter. Theory and numerical results are presented. The basic results are presented in terms of the average optical transfer function of a compensated imaging system and in terms of the average antenna gain of an adaptive-optics laser transmitter, each expressed as a function of the angular separation ϑ between the propagation path along which the reference signal arrives and the propagation path along which the adaptive-optics system is to provide performance. It is shown that for high spatial frequencies (for the compensated imaging system) and for large-aperture diameters (for the adaptive-laser optics transmitter), i.e., large compared with r0/λ and with r0, respectively, the magnitude of the anisoplanatism effect can be characterized by an isoplanatic patch angular size, which we denote by ϑ0. If the angular separation between the two propagation paths is ϑ, it is shown that the optical transfer function and the antenna gain are each reduced by a factor of exp[−(ϑ/ϑ0)5/3]. This simply expressed performance-reduction factor represents an asymptotic limit for high spatial frequencies and for large transmitter diameters. For lower spatial frequencies and smaller transmitter diameters the reduction factor is not so severe. Numerical results are presented to illustrate this.
468 citations
TL;DR: Actuator and mirror design requirements are addressed along with their interrelationship with electronic driver design and projected requirements to meet the demands of future optical systems.
Abstract: The use of adaptive optics has been increasingly proposed as a solution to a variety of optical phase distortion problems. Deformable (rubber) mirror concepts have utilized numerous design techniques for phase distortion correction. Deformable mirror requirements are reviewed for several applications along with projected requirements to meet the demands of future optical systems. Actuator and mirror design requirements are addressed along with their interrelationship with electronic driver design.
80 citations
TL;DR: A system to control the figure of a large telescope primary mirror that is composed of many individual segments is described, employing hexagonal mirrors, to be reliable and effective in continuously maintaining the figure to the precision required for optical astronomy.
Abstract: A system is described to control the figure of a large telescope primary mirror that is composed of many individual segments. The geometry considered, employing hexagonal mirrors, allows a simple and economical control system. The system is shown to be reliable and effective in continuously maintaining the figure to the precision required for optical astronomy.
62 citations
Patent•
17 Jun 1982
TL;DR: In this article, a sensitive wavefront sensor combining attributes of both a Hartmann type of wavefront sensors and an AC shearing interferometer type of sensor is proposed, where diffraction patterns of the first and second gratings are positioned substantially orthogonal to each other to shear the wavefront in two directions to produce two dimensional wavefront slope data for the AC-shearing inter-ferometer portion of the sensor.
Abstract: A sensitive wavefront sensor combining attributes of both a Hartmann type of wavefront sensor and an AC shearing interferometer type of wavefront sensor. An incident wavefront, the slope of which is to be detected, is focussed to first and second focal points at which first and second diffraction gratings are positioned to shear and modulate the wavefront, which then diverges therefrom. The diffraction patterns of the first and second gratings are positioned substantially orthogonal to each other to shear the wavefront in two directions to produce two dimensional wavefront slope data for the AC shearing interferometer portion of the wavefront sensor. First and second dividing optical systems are positioned in the two diverging wavefronts to divide the sheared wavefront into an array of subapertures and also to focus the wavefront in each subaperture to a focal point. A quadrant detector is provided for each subaperture to detect the position of the focal point therein, which provides a first indication, in the manner of a Hartmann wavefront sensor, of the local wavefront slope in each subaperture. The total radiation in each subaperture, as modulated by the diffraction grating, is also detected by the quadrant detector which produces a modulated output signal representative thereof, the phase of which relative to modulation by the diffraction grating provides a second indication of the local wavefront slope in each subaperture, in the manner of an AC shearing interferometer wavefront sensor. The data from both types of sensors is then combined by long term averaging thereof to provide an extremely sensitive wavefront sensor.
61 citations
TL;DR: The decomposition of the wave front into Zernike polynomials provides a means for deriving the rms error of a corrected wave front in analytic form and a step filter approximation is derived.
Abstract: Adaptive optics correction of a wave front by a deformable mirror that acts as a lossless spatial filter is studied. The decomposition of the wave front into Zernike polynomials provides a means for deriving the rms error of a corrected wave front in analytic form. The spatial filter is given in a functional form related to deformable mirror characteristics. A step filter approximation is derived and the conditions where the approximation holds are examined. An example is provided to demonstrate the utility of the spatial filtering concept for adaptive optics systems analysis.
35 citations
TL;DR: A 1-D deformable mirror which uses multilayered PVDF piezoelectric films as the actuators is proposed and the principle of construction and several basic experimental results are presented.
Abstract: A 1-D deformable mirror which uses multilayered PVDF piezoelectric films as the actuators is proposed. First, a set of desired wave fronts is considered and the electrode shape of each film is designed so that the film generates one component of the set. In actual operation of the mirror a combination of the supply voltages is used to control the surface profile. The principle of construction and several basic experimental results are presented.
31 citations
TL;DR: This paper describes a method for using optically tapped, Bragg cell delay lines to implement a general adaptive linear prediction algorithm that can be used in the Fourier domain to achieve a high dynamic range.
Abstract: The transversal filter is widely used in digital data processing In this paper, we describe a method for using optically tapped, Bragg cell delay lines to implement a general adaptive linear prediction algorithm Flexibility is achieved through changing the electronic signals The implementation is in the Fourier domain so that the wide bandwidth of the Bragg cells can be fully used A high dynamic range can be achieved because the system is interferometric and linear in light amplitude
27 citations
04 Nov 1982
TL;DR: In this article, an analysis of the application of active optics of various degrees of complexity to large ground-based telescopes, using field stars as reference sources, is made, and the performance of active compensation systems is evaluated as a function of the number and size of the active zones, reference star magnitude, turbulence strength, and isoplanatic patch size.
Abstract: An analysis is made of the application of active optics of various degrees of complexity to large ground-based telescopes, using field stars as reference sources. The performance of active compensation systems is evaluated as a function of the number and size of the active zones, reference star magnitude, turbulence strength, and isoplanatic patch size. The results show that for nighttime observations, the average field star distribution allows real-time compensation not only for quasi-static wavefront errors due to optical misalignment and mirror figure, but also for image motion, dome seeing, and some atmospheric turbulence effects. Such compensation is especially valuable under good seeing conditions, when residual errors become a significant factor. It is suggested that all astronomical telescopes could benefit from the use of compensation systems with even a small number of active zones. In large segmented-mirror telescopes, the segments themselves can be used to compensate for random wavefront errors occurring in the entire optical path. In fixed-primary telescopes, the same function may be performed with an auxiliary deformable mirror.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
20 citations
TL;DR: A phase correction device has been developed for a high-power cw 10.6-microm laser beam using a water-cooled piezoelectric actuated deformable mirror system to provide dynamic high-speed wave front correction while simultaneously providing high-frequency phase modulation at any or all of its fifty-two actuator locations.
Abstract: A phase correction device has been developed for a high-power cw 10.6-μm laser beam using a water-cooled piezoelectric actuated deformable mirror system. It is the first HEL deformable mirror designed to provide dynamic high-speed wave front correction while simultaneously providing high-frequency phase modulation at any or all of its fifty-two actuator locations. The high voltage amplifiers energizing the deformable mirror can be simultaneously driven at ±500 V from 0 to 100 Hz and at ±50 V from 0 to 2500 Hz about a 500-V bias level. At these drive levels, the controllable surface is capable of assuming nonplanar contours having maximum deformation of ±20 μm, with maximum dither capabilities of ±1 μm at each actuator site and maximum surface gradients of 12 μm/cm. The performance, major features, and design considerations of the mirror and electronics are described.
20 citations
Patent•
09 Feb 1982
TL;DR: In this paper, a rotating beam chopper is used to completely block the outgoing beam, thereby preventing scattered laser light in the optical train and beam expander from drowning out the fainter target return.
Abstract: A time-shared aperture device using the laser illuminated target to provide a return wavefront which passes through the optical train and beam expander. The distortions in this return wavefront are sampled by a rotating beam chopper which completely blocks the outgoing beam, thereby preventing scattered laser light in the optical train and beam expander from drowning out the fainter target return. Wavefront analyzers provide an indication of errors present in the optical system so that correction may be applied.
TL;DR: A compact 2-D deformable mirror is proposed which consists of multiple electrostrictive laminar sheets bonded to the backside of a mirror glass plate and the usefulness of the construction is demonstrated experimentally.
Abstract: A compact 2-D deformable mirror is proposed which consists of multiple electrostrictive laminar sheets bonded to the backside of a mirror glass plate. A set of desired wave fronts is considered; the sheets are assigned to generate each wave front separately. The electrode of each sheet is designed so that the exact voltage distribution required to deform the mirror surface is approximated optimally by a few discrete voltages. In actual operation, the deformation of the mirror is determined by the superposition of properly weighted contributions from all the actuators. The usefulness of the construction is demonstrated experimentally.
TL;DR: A 4-m aperture deformable primary mirror has been designed with the mirror and its supports integrated into a single structure and the results of finite element analyses are described.
Abstract: A 4-m aperture deformable primary mirror has been designed with the mirror and its supports integrated into a single structure The integrated active mirror's minimal weight makes it desirable for a space telescope as well as a terrestrial application Utilizing displacement actuators instead of force actuators, the active controls at the mirror's surface include normal position control and slope control in both the radial and tangential directions at each of forty control points Influence functions for each of the controls are nearly independent, reducing the complexity of the control system Experiments with breadboard models verify the structural concept and the techniques used in the finite element method of computer structural analysis This paper describes the results of finite element analyses
01 Jan 1982
TL;DR: In this article, the authors summarized the nonlinear optical methods allowing one to perform optical phase conjugation, i.e., spatial-phase reversal of an incoming electromagnetic wave.
Abstract: This article summarizes the nonlinear optical methods allowing one to perform optical phase conjugation, i. e. spatial-phase reversal of an incoming electromagnetic wave. Special attention is given to the most powerful technique—to date—which is based on degenerate four-wave mixing (DFWM). One discusses the physical processes (one-photon and two-photon resonances) responsible for DFWM. The generation of light-induced Bragg gratings, and the analogy with real-time holography are emphasized, with a brief review of the applications in adaptive optics and imaging (wavefront rectification, etc.). Also described are the spectroscopic applications of DFWM (transient gratings, Doppler-free emission in gases, high-frequency heterodyne spectroscopy), the polarization properties of phase-conjugate mirrors, and the operation of phase-conjugate resonators.
Patent•
27 Jan 1982
TL;DR: In this paper, a wavefront sensor is used to determine the angle error signal between the wavefront tilt angle and the mirror tilt angle, which is then used to drive the actuator unit.
Abstract: A mirror actuator control system utilizing a wavefront sensor to determine the resulting angle error signal between the wavefront tilt angle and the mirror tilt angle. The resulting angle error signal is used to drive the actuator unit which controls the mirror tilt angle.
TL;DR: A key observation from these experiments was the extreme sensitivity of the HSURIA to perturbations near the resonator optic axis, which is the principal cause of the secondary maxima lock-on problem since the open loop deformable mirror figure must be extremely close to the ideal figure to assure global maximum lock- on by the multidither servo control.
Abstract: An experimental study has been conducted on the ability of intracavity adaptive optics to improve the performance of a half-symmetric unstable resonator with intracavity axicon (HSURIA) by correcting for aberrations from misfigure or misalignment of the intracavity conical optics. When the deformable mirror had adequate spatial frequency correction capability, near diffraction limited far-field performance was achieved, but secondary maxima lock-on by the multidither servo control severely limited the fully adaptive correction capability. A key observation from these experiments was the extreme sensitivity of the HSURIA to perturbations near the resonator optic axis. Variations as small as λ/140 had a significant effect. This perturbation sensitivity is the principal cause of the secondary maxima lock-on problem since the open loop deformable mirror figure must be extremely close to the ideal figure to assure global maximum lock-on by the multidither servo control.
Patent•
01 Mar 1982
TL;DR: In this article, an integrated wavefront compensator for an active optics system is proposed, in which the components for detecting distortions in a wavefront and the component for correcting the detected wavefront distortions are integrated into one unit.
Abstract: An integrated wavefront compensator for an active optics system in which the components for detecting distortions in a wavefront and the components for correcting the detected wavefront distortions are integrated into one unit. The parallel processing channels of the compensator are fabricated simultaneously using simple, solid state components.
TL;DR: In this paper, an optical method for the real time correction of geometrical distortion is reported, based on the "fun-house-mirror effect", where an adjustable nonplanar mirror is introduced between object and pupil-plane and generates a suitable (space-variant) shift of each pixel.
TL;DR: A power spectral density method for calculating the efficiency of modal compensation of wave front phase error caused by propagation through atmospheric turbulence is presented and anisoplanatism is shown to limit the amount of compensation possible with adaptive optics.
Abstract: A power spectral density method for calculating the efficiency of modal compensation of wave front phase error caused by propagation through atmospheric turbulence is presented. The method permits an accurate evaluation of the interactive effects of isoplanatism, outer and inner scale size, control algorithm, servo type, and order of modal compensation on control loop bandwidth requirements. Applications of the method to some typical ground-to-ground and ground-to-space geometries are presented. Anisoplanatism is shown to limit the amount of compensation possible with adaptive optics, particularly in the higher-order aberration modes.
04 Nov 1982
TL;DR: In this paper, the authors describe the results of recent research undertaken to examine the feasibility of employing laser interferametry to precisely measure absolute distance over extended ranges, showing a resolution of 0.03 μm (RMS) for measurements over distances up to 10 meters.
Abstract: This paper describes the results of recent research undertaken to examine the feasibility of employing laser interferametry to precisely measure absolute distance over extended ranges. Results are presented which show a resolution of 0.03 μm (RMS) for measurements over distances up to 10 meters. The technology developed for achieving these results is based on two-color, synthetic Michelson interferometry employing a new CO2 laser source. Indeed, the new laser is the key element in this process: it was specifically designed to sequentially switch between four sets of stable R- and P-line pairs and thereby provide a basis for forming simultaneous equations which were employed to greatly reduce the half wavelength ambiguity typical of single wavelength interferometers. Potential applications to future optical telescopes - particularly the large, multipanel telescopes under consideration for 10-15 years hence - their initial alignment and control, are suggested.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: One of the simplest algorithms for adaptive correction (correction of a random tilt of a wavefront) is considered in the case of a wide optical beam when a point reference source is used as discussed by the authors.
Abstract: One of the simplest algorithms for adaptive correction (correction of a random tilt of a wavefront) is considered in the case of a wide optical beam when a point reference source is used An analysis is made of various algorithms for the determination of a random tilt A calculation is made of the distribution of the average intensity of the corrected field The results are given of an experiment carried out over a near-ground path The problem of correlation of random tilts of a phase front and of high-frequency phase fluctuations is discussed
TL;DR: An iterative optical matrix-vector processor that computes the adaptive weights for a phased array radar is described and is found to perform quite adequately and to be most appropriate for advanced multidimensional adaptive phased array radars.
Abstract: An iterative optical matrix-vector processor that computes the adaptive weights for a phased array radar is described. Multidimensional adaptivity in both target angle and velocity is achieved by lexicographically ordering the antenna elements as they are fed to the optical processor. Complex weights are computed by spatial multiplexing of the vector and matrix inputs to the system. The error sources of the optical system and the convergence of the iterative algorithm are analyzed, and experimental demonstration of the accuracy and performance of the system is included. This novel processor is found to perform quite adequately and to be most appropriate for advanced multidimensional adaptive phased array radars.
04 Nov 1982
TL;DR: In this article, an active mirror was developed which consists of an electrostatically deformable membrane with 5 cm in diameter, which is elongated by an electrode array with 63 hexagonal elements arranged in a ring structure.
Abstract: The light propagation through the atmosphere limits the high angular resolution in astronomical imaging. Active optics is a method to overcome this problem. It allows a real-time optimization of the resolving power. An active mirror was developed which consists of, an electrostatically deformable membrane with 5 cm in diameter. The 0.5 micron thick aluminized polymer foil is elongated by an electrode array with 63 hexagonal elements arranged in a ring structure. The sensitivity is in the region of 0,05 microns per volt. It works up to 4 kHz without resonances. The maximum local tilt of the membrane is 3 microns per 5 millimeter. For an atmospheric tilt compensation of the wavefront the mirror housing is in a gimbal-mount. Piezo-electric actuators provide a total mirror angular movement up to 20 Hz and angular sensitivity of 77 arcsecs per kV. With this active mirror device and a multiprocessor-microprocessor control unit the stabilisation of the star-speckle pattern positions and the deconvolution of the speckle patterns are possible. Two control methods are in development and analized in comparison. One of them is working with a modified shearing interferometer as a wave-front sensor and a feedback with cross-talk compensation. The other is sensing the optical information in the image plane by a diode-array and estimating the wave-front by trial and error or different more sophisticated algorithms. The previous system is designed for the 0,75 m RC-telescope with alt-az mount at the Landessternwarte in Heidelberg, FRG.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
04 Nov 1982
TL;DR: In this article, the atmospheric turbulences are taken into account by extending the local differential operator in an "observer"-like structure, and the coefficients of the approximating functions, each of which corresponds to a certain mode of the mirror surface, are fed back to the actuators by a modal control matrix.
Abstract: In adaptive optics, the compensating phase distribution can be generated by an expansion of the turbulence phase distortions into modes of a set of basis functions, i.e. Zernike-polynomials and Karhunen-Loeve-functions. By applying a modal control concept to a practical adaptive optical system, the electrodes of a membrane mirror can be controlled in parallel with greatly reduced cross-talk. The coefficients of the approximating functions, each of which corresponds to a certain mode of the mirror surface, are fed back to the actuators by a modal control matrix. The atmospheric turbulences are taken into account by extending the local differential operator in an "observer"-like structure.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, an experimental investigation of an adaptive interferometer with correction of the wavefront tilts is presented, and the problems of organization of control in adaptive inter-ferometers are discussed.
Abstract: An analysis is made of the possibility of using adaptive optics techniques in laser interferometers. The influence of wavefront distortions, caused by atmospheric turbulence, on the operation of interferometers is studied. The problems of organization of control in adaptive interferometers are discussed. The results are given of an experimental investigation of an adaptive interferometer with correction of the wavefront tilts.
01 Nov 1982
24 Mar 1982
TL;DR: In this paper, an extension of the LINNIK point diffraction interferometer to 253.7nm was presented, and the possibility of working at soft X-ray wavelengths is considered.
Abstract: Previous work has demonstrated the use of the LINNIK Point Diffraction Interferometer for the measurement of wavefront error in soft x-ray imaging systems. Operational wave-lengths from 632.8nm (He-Ne) down to 313.1nm (Hg) have been used. This paper describes our extension of the technique to 253.7nm together with a demonstration. of feasibility at 121.6 nm (Hydrogen. Lyman-α), we believe for the first time. Finally the possibility of working at soft X-Ray wavelengths is considered.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: Tests with a two-degree-of-freedom system operated in turbulence demonstrate that the artificial-glint technique allows effective convergence at propagation distances reaching far into the scintillation-saturation region, i.e., well beyond the theoretical limit.
Abstract: The conventional feedback of multidither outgoing-wave adaptive optical systems is inoperative in the presence of a featureless target resolved by the transmitter optics. We propose in this paper to define an artificial glint by imaging the target laser pattern on a pinhole aperture. The concept is somewhat obvious, but in turbulence the existing theory on resolution and coherence states that it is restricted to small scintillation strength. Through correlation measurements between the physical-glint return and the artificial-glint irradiance, it is shown that the range of validity is much broader than predicted. Furthermore, tests with a two-degree-of-freedom system operated in turbulence demonstrate that the artificial-glint technique allows effective convergence at propagation distances reaching far into the scintillation–saturation region, i.e., well beyond the theoretical limit.
01 May 1982
TL;DR: In this paper, the effect of four error sources on the performance of an adaptive optics system used to compensate for the effects of atmospheric turbulence on the propagation of visible wavelength laser radiation between a ground-based transmitter and a space-borne receiver was investigated.
Abstract: : Computer simulations were performed to determine the degree of correction achievable with phase-conjugate adaptive optics. The purpose was to investigate the effect of four error sources on the performance of an adaptive optics system used to compensate for the effects of atmospheric turbulence on the propagation of visible wavelength laser radiation between a ground-based transmitter and a space-borne receiver. The four error sources considered were: (1) finite spatial bandwidth corrector mirror; (2) finite temporal bandwidth servo system; (3) measurement noise; and (4) anisoplanatism. We investigated both the separate and combined effects of these errors. Results obtained when the errors were introduced separately agree well with the predictions obtained from the analytical relations used to represent these effects in the SLC (strategtic Laser Communication) Uplink model prepared for use in systems calculations. As expected, we found that when all the errors are present simultaneously their effects are not always accurately modeled by these analytical relations. This is particularly true in the case of the effects of having finite spatial and/or temporal bandwidth in combination with those due to anisoplanatism. In such cases, the Strehl ratio obtained in the simulations was up to a factor of two higher than that predicted by the SLC Uplink model analytical relations.
04 Nov 1982
TL;DR: In this article, the authors examine the possibilities for these technologies impacting the design of the NGT and suggest that attention should begiven to the use of more, and smaller segments to achieve a maximal cost/benefit ratio.
Abstract: SummaryThe segmented mirror technology is being pursued as a corrector of atmospherically induced wavefront distortions. As a result, mirror fabrication techniques, actuation techniques and alignment concepts will bedeveloped and validated. '.`1e examine the possibilities for these technologies impacting the design of the NGT. Questions raised center around the perception that the primary would be lighter if the number of segmentswere increased. If the segment alignment problem were acceptably solved, we suggest that attention should begiven to the use of more, and smaller segments to achieve a maximal cost /benefit ratio.References 1. "Ground -to -Space Optical Power Transfer," G. E. Meyers, C. L. Hayes, J. F. SooFoo andProceedings SPIE, Vol. 141, p. 108. 1978.R. M. Stubbs, 2. "New Developments in Deformable Surface Devices," J. H. Everson, Proceedings SPIE, Vol. 141, p. 11,1978. 3. RADC Contract No. F30602 -82 -C -0006. 4. "Telescope Alignment with the Absolute Distance Interferometer," N. A. Massie and M. R. Dunn, SPIEProceedings, Vol. 332, 1982.SPIE Vol. 332 Advanced Technology Optical Telescopes (1982) / 379