Showing papers on "Adaptive optics published in 1985"

Wavefront sensing deconvolution and adaptive optics

Abstract: For large telescopes, the fundamental limit set by the diffraction to the angular resolution can be reached if the aberrations are perfectly corrected. Two solutions are practicable: image restoration by numerical processing or real time correction by adaptive optics. These two processes require the determination of the wavefront or of the optical transfer function. New large detectors arrays can be used in wavefront sensing which then allow the measurement of the wavefront at a large number of point. The general lay-out of such an instrument is given and its accuracy evaluated. The wavefront sensing contribution to numerical image processing is studied mainly for the case of degradation by atmospheric turbulence. The improvement of numerical processing by a partial active correction is discussed.

Thermal distortions of focused laser beams in the atmosphere.

Abstract: A systematic theoretical investigation of thermal self-action of focused cw laser beams has been carried out. A modification of the splitting method, having high accuracy and operation rate, has been developed for a numerical solution of the nonstationary 4-D self-consistent problem. The following are considered: optimization of the focusing parameters at thermal self-action in moving media; blooming of cylindrically focused beams; influence of wind velocity fluctuations on thermal distortions; programmed scanning with the beam along a given path; adaptive phase-conjugate correction of nonstationary thermal defocusing of the beam. In conclusion the results are discussed.

Lasers with wavefront-reversing mirrors (review)

Abstract: The principles of construction of lasers with wavefront reversing (WFR) mirrors are considered. Descriptions are given of methods for the determination of the transverse and longitudinal mode structures in such lasers. The advantages and shortcomings of various systems with WFR mirrors are reviewed. A comparison is made of the various systems with one another and with conventional mirrors. The future trends and the main lines of further research are forecast.

Unconventional adaptive optics

Abstract: An improved adaptive optics system is disclosed for correcting atmospheric phase aberrations. A satellite (10) laser beacon is operated at the Stokes shifted Raman wavelength. After passing through the atmosphere (A), the signal is phase conjugated (16) and amplified in the Raman amplifier (12). The result is a high energy laser beam with phase conjugated aberrations which may be returned to the satellite (10).

Surface analysis of an actively controlled telescope primary mirror under static loads.

Abstract: The performance of an actively controlled mirror with an aspect ratio of 63:1 is modeled by a large scale software system. The model allows generalized static disturbances to be applied to the mirror, generates a corrective force field, and tests the result through a finite element simulation. For convenience in input, disturbances may be in the form of a force field or a displacement field. Use of a displacement field is easier, for example, if one wishes to distort the mirror with a particular aberration term for which the disturbing forces are unknown. The user must have established a particular actuator set to be used in counteracting the disturbance, whereupon the actuator forces for this set are determined by a modal truncation method. These computed actuator forces are then reapplied to the mirror model along with the disturbance to evaluate the corrected behavior of the model. Comparisons are made of the rms surface errors and energy concentrations as predicted by modal truncation and computed via the finite element method. Numerical examples, including some bordering on the pathological, are employed to show that the corrected mirror performance under the action of computed actuator forces and external disturbances agrees generally with the mirror surface as predicted by modal truncation.

Investigation of a ccd wave front sensor of an adaptive optics radiation focusing system

Abstract: Results are presented of the investigation of a wave front sensor, based on a linear charge-coupled device, for an adaptive optics system intended to monitor the surface shape of the front corrector and to control the focusing of the optical radiation. A method is described for measuring the location of the energetic center of gravity of the optical image to (2p)/sup -1/ accuracy, where p is the number of phase electrodes in an individual element of the photosensitive ccd-structure. Application of an adaptive optics system of ccd structure with a large number of elements in a wave front sensor permits reduction of the relative error in measuring the location of the center of gravity of the distribution and the beam defocusing less than or equal to 0.1%.

Finite Element Methods For Evaluating Optical System Performance

Abstract: Many aspects of geometric optics and wave optics are compatible with the finite element method of analysis. This fact provides a new and powerful tool in the fields of optomechanical design and optical systems engineering. Using special features available in some commercially available finite element codes, it is possible to include optical system parameters as a portion of the finite element model. The simultaneous solution of the optical and mechanical problems provides higher accuracy and consistency of the results, efficient calculation of many different load cases, and solutions to optics design problems which are difficult or impossible to handle in traditional lense design codes. This paper shows results possible in commercially available finite elements codes used to calculate optical system parameters, including surface figure changes, generalized optical ray tracing and wavefront error computation. The paper is illustrated with examples drawn from recent practice.

Opto-electronic analyser for wave surfaces with microlens mosaics

Abstract: A system for correcting wave surfaces comprises adaptive optics and a phase distortion detector for a wave surface. It is characterised in that the phase distortion detector comprises a mosaic of microlenses (20) onto which an image is projected, a mosaic of detectors (25) situated in the focal plane of the mosaic of microlenses, the detectors delivering electrical signals, a device for calculating the Fourier transform of the said signals and means of applying the said Fourier transform to the adaptive optics. This system can be used in the scope of aiming laser beams or very-long distance imaging.

Effect of multipath and scattering on array gain of a large adaptive beam forming phased array

Abstract: An adaptive antenna array system large enough to obtain angular resolving power comparable to common optical systems is called a radio camera. Following an adaptive beam forming procedure the beam is open-loop scanned to get the desired images. Multipath and scattering of the energy reradiated from the target induce phase-front distortions. A theory has been developed showing that the loss in array gain due to the scattered field can be described by a simple relationship involving only two quantities: the strength S of the scattered field relative to the direct field and a spatial correlation function \rho(\theta) associated with the scattering process. The argument \theta is the scanning angle. The array gain is G(\theta) = G(0)S[1-\rho(\theta)] . A series of experiments has been conducted to test the assumptions underlying the development of the theory, which appears to vindicate them. The theory and experiments are described. The theory is then used to determine the degradation in radio camera scanning performance for several important cases of interference caused by reflections.

High Resolution Solar Observations

Abstract: Traditionally the way to get high Quality images has been to find a good seeing site and establish a high quality observatory. It now appears that this procedure can be improved by installing active mirrors which correct real time wavefront tilt, and adaptive mirrors which correct, at least for a limited field of view, wavefront distortions introduced by the atmosphere. Space telescopes offer the further advantage of completely eliminating the blurring and distortions introduced by the atmosphere. Further space operations offer the possibility of uninterrupted observing sequences of many days or weeks.

Charged-large-array-flexible mirror.

Abstract: A charged-large-array-flexible (CLAFLEX) mirror is a new concept for the deformable mirror. This mirror consists of a continuous piezoelectric transducer sheet whose thickness is controlled by one or more electron beams. A CLAFLEX mirror can be controlled using image-intensifier or video devices and digital image-processing techniques. A 100 × 100 array of deformable mirror elements can be controlled with state-of-the-art components, making short-wavelength high-power laser-beam steering, focusing, and phase conjugation practical. Two different CLAFLEX mirror control schemes are described. One uses a scanning electron beam; the other uses multiple parallel electron beams. Both designs use phase-lock control circuits that are synchronized by first phase locking a small central region of the mirror and then expanding this region (using an iris diaphragm) until the entire CLAFLEX mirror is phase-locked on the same wave front. A CLAFLEX mirror can be steered and focused optically by biasing the interference intensity distribution using an external light source. A wedge-shaped intensity bias, for example, will tilt the CLAFLEX mirror.

Universal wavefront sensor apparatus

Abstract: A wavefront sensor apparatus for a large optical system, such as a telescope, having a reticle with at least one slit therein to provide image signatures for various portions of the aperture to an array of infrared sensor cells. The time differences between the image signatures represents relative image displacement caused by the wavefront slope variation in the actual wavefront.

Modified quasi-serial multiplier

Abstract: Technique permettant de rendre plus rapide la multiplication quasi-serie dans les processeurs optiques

Optical Transfer Function Computer Model For Imaging Systems

Abstract: A computer model based on the optical transfer function (OTF) approach has been developed and implemented for analyzing imaging systems looking through the atmosphere. It is interactive and graphics oriented, and can be used to perform quick-look image quality trade studies on scenarios involving various optical system parameters, atmospheric conditions, and target and detector sizes.

Compensation of nonlinear distortions of light beams in a moving medium

Abstract: The efficiency of compensating nonlinear distortions in a moving medium is investigated in the case of control by inclination and focusing of the light beam. Within the framework of an aberration-free description of optical radiation propagation, the operation of an adaptive system in different quality criteria is investigated, as well as the peak intensity, the location of the beam center of gravity, the power received at a given aperture, etc., the check-out modes are determined for focusing and inclination of a light beam wave front, and recommendations are given for increasing the fast-response.

IR Background Speckle Noise Induced by Adaptive Optics in Astronomical Telescopes

Abstract: The infrared emission of astronomical sources is buried in a large background due to the thermal emission of the telescope. The real time deformations of an adaptive flexible mirror are likely to produce a spurious modulation of this background, adding noise to the signal. We estimate here the amount of noise introduced by such a mirror.

Contorted mirror reduction of projected image distortion.

Abstract: An analysis is made of the degree to which a simple contorted mirror can reduce distortion in a projected image. Although it is impossible in general to remove the distortion completely by this means, significant reduction may be achieved. Equations are derived for the shape of a mirror which will give the maximum reduction possible. Equations are also developed for how to stress a planar mirror to create the desired optimal shape. Image blurring is estimated. An example is presented in which this technique is used to reduce the distortion which results when a projection lens appropriate for projection onto a flat screen is used instead to project onto a spherical surface from an oblique angle.

Sensor for the detection of image defects

Abstract: SENSOR FOR ADAPTIVE OPTICS WITH PHASE CORRECTION OF OPTICAL AND FOR DETECTING DEFECTS IMAGE REPRESENTS AN OBJECT, WITH AN OPENING INPUT DIVIDED IN SMALL OPENING FOR MULTIPLE REPRODUCTION OBJECT AND AS DETECTORS opto WITH SMALL OPENINGS. SENSOR IS EQUIPPED WITH A NETWORK SENSORS opto 3 HIGH POWER OF RESOLUTION ON WHICH THE INDIVIDUAL PRINTS are juxtaposed SO THAT THEIR POSITION ON THE GEOMETRIC BY EACH COMPARED TO OTHER MAY BE DETERMINED BY A correlator ANALOG 4.

Allowance for quantum noise in adaptive focusing of optical radiation

Abstract: An analysis is made of the problem of adaptive focusing of optical radiation on a point-like object across a turbulent atmosphere. The Bayes approach is used to obtain an algorithm for the control of the average tilt of the wavefront on the transmitting aperture. The control is performed using a priori information on the atmosphere and on the coordinates of the object, as well as information on the radiation emitted by the object which is assumed to be luminous. A study is made of the influence of quantum noise in the signal recording process on the quality of adaptation.

Systems of equations fo zonal wavefront recovery in adaptive optics

Abstract: The basic results obtained in the present work may be stated as follows: 1) a method of obtaining the analytical solution of the systems of difference equations arising in problems of zonal wavefront recovery is described; the expressions obtained may be used for a noniterative algorithm of solution of the given systems; 2) the possibility of choosing an optimal recovery algorithm in accordance with the system characteristics of the adaptive instrument and the phase fluctuations of the detectable field is shown; 3) analytical expressions are obtained for the recovery error due to measurement noise, depending on the dimension of the mass of recovered phase values; the agreement between Eqs. (24), (26), and (28) and the results of numerical solution of the given systems in [10, 11] is complete.

Adaptive Telescope Design Using Computer Tools

Abstract: Large-aperture lightweight space optics must be designed from first principles so as to compensate for a multitude of disturbing influences if they are to perform to approximate theoretical perfection during a long period of life. Active control of structures and active optical components such as deformable mirrors are vital when dynamic performance is an issue. This overview deals with a hypothetical (but not unreal) nominal system, handling disturbances, and adaptive optics. The 2.4-meter Hubble Space Telescope primary mirror is held up as an example of an active deformable mirror designed with the latest mathematical tools.

Integrated Optical Wavefront Sensor

Abstract: This paper presents a design for an integrated optical wavefront sensor. Light from an aperture is focussed by a lens onto a detector array. The resulting signals can be used to determine the amount of angular tilt of the wavefront. Parameters affecting angular resolution are analyzed. Tilt angles as small as 10 -5 rad are detectable. The effect of wavefront curvature is also discussed.

Fast-acting adaptive mirrors and their efficiency at compensating for random phase perturbations

Abstract: Research in adaptive optics represents a new stage in the development of optical systems. Adaptive optics can be used for compensating for phase fluctuations of a light field propagated through the atmosphere and through optical media. The idea of dynamic compensation of phase fluctuations originated in the 1950s [1] as an effort to improve the resolutions of telescopes designed for observing stars through the turbulent atmosphere. However, the technological level required for applying this technique to detection and transmission systems has only recently been achieved with the successful development of fast-acting optical elements — adaptive mirrors [2].