Showing papers on "Adaptive optics published in 1981"

Intracavity adaptive optics. 1: Astigmatism correction performance

Abstract: A detailed experimental study has been conducted on adaptive optical control methodologies inside a laser resonator. A comparison is presented of several optimization techniques using a multidither zonal coherent optical adaptive technique system within a laser resonator for the correction of astigmatism. A dramatic performance difference is observed when optimizing on beam quality compared with optimizing on power-in-the-bucket. Experimental data are also presented on proper selection criteria for dither frequencies when controlling phase front errors. The effects of hardware limitations and design considerations on the performance of the system are presented, and general conclusions and physical interpretations on the results are made when possible.

Effects of piston and tilt errors on the performance of multiple mirror telescopes

Abstract: The degradation due to random segment jitter and phase mismatch on the average far field, on axis irradiance of a laser beam transmitted from a telescope with a segmented primary mirror is computed The derived expression is exact within the stated assumptions and offers a more accurate alternative, for this application, to the commonly used Strehl approximation© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Deformable Mirrors For All Seasons And Reasons

Abstract: The use of adaptive optics has been increasingly proposed as a solution to a variety ofoptical phase distortion problems. Deformable (rubber) mirror concepts have utilized numer-ous design techniques for phase distortion correction. Deformable mirror requirements arereviewed for several applications along with projected requirements to meet the demands offuture optical systems. Actuator and mirror design requirements are addressed along withtheir interrelationship with electronic driver design.Introduction"Mirror, Mirror, on the wall, who is the fairest of them all," is a quote from a well knownfairy tale. The quote can also apply to an active optic used to solve a variety of opticaldistortion problems by reshaping an optical phasefront with controllable optical path dif-ferences. The specific active optic, which is the subject of this paper, is the deformableor "rubber" mirror. A wide range of deformable mirror concepts and possible applicationshave been proposed for tracking, auto focus, image enhancement, and turbulence correction.Which one of these concepts is the best ( "fairest ") depends on the requirements of the spe-cific application.The earliest reported use of "active" optics occurred in 211 BC, as depicted in Figure 1.Archimedes used a segmented "deformable mirror" actuated by the defending Greeks to destroyan attacking Roman fleet during the siege of Syracuse.1-3 Another concept proposed for thediet conscious, but unsuccessful, individual is a continuous deformable mirror which trans-forms a distorted object into a pleasing real image as shown in Figure 2. Although these con-cepts do not reflect the present state -of- the -art of deformable mirrors for use in high energylaser (HEL) or astronomical adaptive optical systems, the two basic techniques of a continuousand a segmented mirror are representative of present -day concepts.Figure 1. Archimedes' adaptive opticalsystem using segmented mirror elements.

Adaptive techniques for precise detection of the coherence function by an intensity triple correlator.

Abstract: An adaptive technique for precise detection of the coherence function by intensity triple correlation is proposed. Adaptive change of the sampling interval and the calculation of differential phase in the transformed domain are used in this method so that the correct coherence function can be extracted even from fairly noisy data. Numerical analyses as well as experimental results show the effectiveness of the method.

Alignment And Evaluation Of The Cryogenic Corrected Infrared Astronomical Satellite (IRAS) Telescope

Abstract: Room temperature alignment and evaluation techniques for the Infrared Astronomical Satellite (IRAS) telescope which has a primary mirror figured to correct for surface distortions at the 2 K operating temperature will be discussed. Interferometric cryogenic testing of the 0.6 meter, f/1 .5 light-weighted beryllium primary mirror at its intended operating temperature revealed surface distortions that could be modeled with Zernike polynomials. With this model, it was possible to derive the -inverse- of the cryo wavefront error (ideal cryo mirror) and figure the cryo correction into the primary mirror using Perkin-Elmer's Computer Controlled Polisher. It was recognized that during room temperature assembly of the system, misalignment of the secondary mirror could introduce additional unwanted aberrations that would cancel or distort the wavefront errors purposely intro-duced by the cryo figuring. To avoid this possible degradation and to ensure optimum telescope performance, the system Zernike polynomial coefficients and wavefront maps generated from the in-process alignment interferograms were monitored and compared to Zernike coefficients and wavefront maps for the cryo corrected primary mirror. Using Zernike polynomials to monitor the optical quality of the telescope enabled figure and alignment errrors to be monitored, and demonstrated that the alignment tolerance was achieved.

An All-Reflective Zoom Optical System For The Infrared

Abstract: Development and test work in the laboratory frequently requires variation of the size and radiative characteristics of a source which is used to provide the radiant power for effects or detection studies. To provide this capability, a system of multiple moving mirrors has been designed for use in optical beam shaping and image manipulation arrangements applied in optical diagnostic procedures and testing of optical sensor systems. Its particular features are a zoom capability of 30:1 and a total scaling range of 800:1, so that approaching or receding sources can be simulated in the laboratory. In addition, the effective source area and with it the accepted radiative flux can be varied over a range of five magnitudes. A detailed analysis of the system and its in-herent wavefront aberrations is given; the dynamic requirements, and methods to improve the optical performance of the mirror system are discussed.

Effects Of Mirror Surface Ripple On Image Quality

Abstract: Mirror surface ripple acts as a phase grating to diffract light out of the central maximum of the point spread function (PSF), reducing image quality. The effects of ripple on image quality are examined with the aid of computer simulations using rotationally symmetric wavefront error models, and through interferometric measurements of a mirror known to have significant surface ripple. Image quality is evaluated in terms related to the performance requirements of large orbital astronomical telescopes that must perform in both ultra-violet and visible light. Techniques for measuring and specifying ripple are discussed.

Three-Actuator Deformable Water-Cooled Mirror

Abstract: A new method for dynamically deforming a thin mirror to correct the phase aberration function for defocus and astigmatism is presented. Three piezoelectric-type actuators, attached to the back edges and parallel to the front surface of the mirror, induce edge moments that bend the mirror to its desired shape for correction of the aberrated wavefront. A three-actuator deformable water-cooled mirror breadboard has been designed and built. Major features, design constraints, and performance expectations of the deformable mirror design are described.

Target loop adaptive optics: thermal blooming correction.

Abstract: To evaluate adaptive optics (AO) concepts for the correction of nonlinear atmospheric phenomena occurring in high energy laser beam propagation and to perform AO system trade offs, a simple, but reasonably accurate, model of the entire AO loop is required. Heretofore, no such model existed which takes into account the temporal response of the atmosphere and yet is simple enough to permit extensive system tradeoffs. We have developed such a model. Optimum thermal blooming correction dictates that the atmospheric response time must be accounted for properly, especially for strong blooming strength. Experimental verification of the above model was carried out using an argon-ion laser with an iodine blooming cell and a closed AO loop to provide corrections for tilt, focus, and astigmatism. Reasonable agreement between theory and experimental data was achieved.

Medium Induced Phase Aberrations In Continuous Wave (cw) Hydrogen Fluoride Chemical Lasers

Abstract: Continuous wave hydrogen-fluoride lasers designed to yield high mass to power utilization efficiency contain active medium inhomogeneities which have the potential of introducing large correlated medium aberrations. Reduction of the magnitude of the correlated medium aberrations by proper orientation of adjacent laser nozzle modules are investigated using geometric and diffractive wave optics analysis. Two significantly different high mass efficiency designs were examined, the axisymmetric and hypersonic wedge. Detailed gas dynamic calculations were made to estimate the index of refraction variations in these three-dimensional mixing, reacting and lasing flowfields. The geometric and diffractive wave analyses were performed to establish the optical path differences (OPD's) introduced by multiple rows of the basic nozzle array unit. Comparisons between the geometric and diffractive analyses showed that the geometric treatment would place an upper limit on the OPD's to be expected from multiple nozzle arrays. Alignment of rows of the axisymmetric nozzle array with the lasing axis was found to have a catastrophic effect on the beam quality of the device. However, by properly skewing the rows of nozzles, it was possible to reduce the degradation in beam quality. Similarly, worst case orientations for the hypersonic wedge array were identified and skewing of the trailing edge of the hypersonic wedge with respect to the optical axis was shown to significantly minimize beam quality degradation.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Bubble forming media for optical recording: A new approach

Abstract: Characteristics and performance of a novel optical recording material in which information is recorded by surface deformation are described. This deformation recording material (DRM) has a high sensitivity (0.5 NJ/U2) independent of wavelength and adapted for use with a low-power He-Ne or diode laser. As opposed to ablative-type material, DRM type gives sharp clean reproducible recorded points free of relief rims and debris, which make possible carrier to noise ratio as high as 65 dB within 30 kHz for frequencies in the IO-15-MHz range. Repetitive readout is possible below recording threshold without alteration. DPM-type media enable direct replication of metallic copy by an electrolytic process or plastic copy by a cold moulding process. DRM media are well adapted to recording of broadcast quality video or high data rate and have good archival properties. (13 min)

Wavefront Sensing And Control Aspects In A High Energy Laser Optical Train

Abstract: In this paper we review the major elements of a HEL wavefront sensing and control system with particular emphasis on experimental demonstrations and hardware components developed at Lockheed Missiles & Space Company, Inc. The review concentrates on three important elements of wavefront control: wavefront sampling, wavefront sensing and active mirrors. Methods of wavefront sampling by diffraction gratings are described. Some new developments in wavefront sensing are explored. Hardware development efforts of fast steering mirrors and eage controlled deformable mirrors are described.

Aberrations In High Power Laser Systems

Abstract: The function of a high power laser system is simple in nature: generate coherent radiation, transport and point it through an optical system and finally deliver it to a receiver plane where its function, be it fusion, be it welding, or whatever, is accomplished. While the specific nature of the elements of every system may be different depending greatly on requirements such as power levels, and wavelengths, it is almost always true that if the coherent nature of the laser radiation is to be used to maximum advantage, very careful optical tolerances must be placed on every step of the laser system design and operation.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Linnik Point Diffraction Interferometer Of Increased Sensitivity For The Measurement Of Wavefront Error

Abstract: The 1933 LINNIK Point Diffraction Interferometer continues to offer new possibilities in non-contacting aspheric grazing incidence mirror testing. In this work we demonstrate the wave-front aberration of a stigmatic Soft X-Ray reflecting optic recorded at progressively shorter wavelengths to a current limit of 313 nm yielding a twofold increase in sensitivity over previously reported measurements.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical Distortion And Far Field Measurements For Laser Window Materials

Abstract: Laser -induced optical distortion in laser window materials may seriously impair theperformance of a high power optical system. The distortions result from refractive indexchanges produced by laser- induced thermal gradients. The thermo -optic effect (dn /dT),thermal expansion, and stress -optic effect all contribute to the loss of far fieldintensity. Experimental measurements of thermal lensing in ZnSe and experiments to monitorthe distortion of laser- irradiated fluoride materials are presented. For a well behavedGaussian beam profile the window distortion produces a thermal lensing effect in ZnSe whichchanges the focus but produces only slight distortion; refocusing of the optical system canrestore the on- target intensity in this situation. In general, the laser -induced dis-tortions will follow the beam profile variations. Irregular beam intensity profilesintroduce greater distortion than uniform beam profiles.IntroductionThermal lensing and thermally induced distortion produced by the propagation of a laserbeam through an absorbing medium have been recognized as a limiting factor in obtaininghigh intensity at the focal plane of a laser optical system.' Theoretical and analyticalinvestigations of this phenomena were conducted2 which showed the influence of variousmaterials parameters (refractive index, n; thermo -optic coefficient, dn/dT; expansioncoefficient, a; and stress optic coefficients, qi

Radiance Profile Enhancement for Solar Occultation Measurements

Abstract: Distortions in received signals in solar occultation measurements made from space arise as a result of the systematic motion of the electro-optical sensor. In a wide range of cases, the motion-related signal distortions caused by the instrument's full modulation transfer function are as important as those from the optics. This paper demonstrates by simulation that existing techniques in the field of digital-image processing can be applied directly to solar occultation experiments to correct for these distortions. The resulting enhanced radiation profile is much closer to the true radiance profile than is the sampled output of the instrument. Use of this enhanced radiance profile in the inversion computation should improve the retrieved atmospheric profiles considerably. It also contains a study of the accuracy of such application from the point of view of instrument noise, uncertainties in the knowledge of the instrument function, and the nature of the power spectrum of the undistorted signal.

Adaptive Optics Compensation Of Thermal Distortion

Abstract: The capability of a conventional inertial adaptive optical system in compensating for thermal distortion is examined. Since thermal irradiance mapping is a process that transfers anomalies in intensity to aberrations in phase, adaptive optics are particularly useful. Both linear spatial filtering and variance minimization methods of analysis will be discussed. The linear spatial filtering concept will be applied to the specific problem of thermal irradiance mapping and shown to be equivalent, within the system constraints, to a least-squares fit of the deformable mirror surface to the wavefront. The special cases of Gaussian beams, annular beams, and irradiance profiles which can be expanded into Zernike polynomials will be studied in detail.

Adaptive Optics--Problems And Prospects

Abstract: This paper briefly reviews the application and limitations of adaptive optics using discrete components to the problems encountered in high-power laser beam conditioning. These problems include static surface figure errors, randomly varying wavefront aberrations due to thermal distortion of the optics, and inhomogeneties within the laser cavity, as well as precise pointing of the beam in the presence of vibration. The capabilities of current devices such as deformable mirrors and wavefront sensors are reviewed. The prospects for removing some of these limitations are considered.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Advanced Wavefront Sensor Concepts.

Abstract: : The objective of this effort was to investigate advances in wavefront sensor technology for use in future adaptive optics systems. The improvements sought over presently developed adaptive optics systems are preliminary in the areas of component efficiency and sub-system complexity, since this would have potential for major operational simplicity and reduced cost. The concept under study in this effort is the Large Scale Integrated Imaging Irradiance (LSI3) sensor. This is based on the Integrated Imaging Irradiance (I3) sensor (U.S. Patent No. 4,141,652). The I3 sensor is based on the Hartmann concepts, but does not suffer from the optical alignment problems inherent to previously developed Hartmann sensors. Another of the major advantages of the LSI3 sensor over the Hartmann sensors (including the previously developed I3 sensor) is that the LSI3 sensor utilizes the full aperture of the system in dividing the input photon flux into the respective quadrants which results in better diffraction - limited resolution. The LSI3 sensor is based on an optical system that is independent of the number of sub-apertures selected. The major tasks of this study included the conceptual design of a small version (approximately 20 channels), a large scale (approximately 200 channels) wavefront sensor, and the evaluation of the expected performance, complexity, and cost of these prototype models. The result of these design advancements is a new wavefront sensor (LSI3) which could provide cost and performance advances for future adaptive optics systems.

Alignment System For Advanced Laser Resonators

Abstract: A methodology for advanced laser resonator alignment systems has been developed. The resonator alignment approach maintains acceptable phase quality of the output laser wavefront in the presence of optical element misalignment. The advanced laser resonator was of the Half Symmetric Unstable Resonator with Internal Axicon (HSURIA) configuration. The effects on wavefront quality of optical element misalignment in angle and translation were determined for this resonator configuration. The methodology for the alignment system was based on the misalignment sensitivity analysis. Perfect resonator alignment can be achieved only by optical element motion equal and opposite to the misalignment error. For resonator misalignments occuring at each optical element location, the requirements on the alignment system can become untenable. Adequate resonator alignment can be achieved by the introduction of wavefront aberrations which compensate those arising from resonator misalignment. The compensatory wavefront aberrations can be achieved by optical element motions which are different from the resonator misalignment. Residual wavefront error will be presented for a compensatory alignment system applied to the HSURIA resonator configuration. Acceptable residual errors can be achieved by an alignment system in which only two mirrors are controlled in angle.

Aberrations and focusability in large solid-state-laser systems

Abstract: Solid state lasers for fusion experiments must reliably deliver maximum power to small (approximately .5 mm) targets from stand-off focal distances of 1 m or more. This requirement places stringent limits upon the optical quality of the several major components -- amplifiers, Faraday isolators, spatial filters -- in each amplifier train. Residual static aberrations in optical components are transferred to the beam as it traverses the optical amplifier chain. Although individual components are typically less than λ/20 for components less than 10 cm clear aperture; and less than λ/10 for components less than 20 cm clear aperture; the large number of such components in optical series results in a wavefront error that may exceed one wave for modern solid state lasers. For pulse operation, the focal spot is additionally broadened by intensity dependent nonlinearities. Specific examples of the performance of large aperture components will be presented within the context of the Argus and Shiva laser systems, which are presently operational at Lawrence Livermore National Laboratory. Design requirements upon the larger aperture Nova laser components, up to 74 cm in clear aperture, will also be discussed; these pose a significant challenge to the optical industry.

Applications Of Active Illuminators To Adaptive Optics For Laser Systems

Abstract: This paper describes an approach for computing the illumnator power requirements of an active return wave adaptive optics system such as would be used in a long-range laser system. The illuminator power is related to the number of degrees of freedom in the adaptive optics (e.g., number of subapertures) and to the laser system beam quality requirements.

Compensation of coherence effects in an optical spectrum analyzer

Abstract: An optical technique is described which is capable of compensating the effects of imperfect spatial coherent illumination on the performance of a modified Mach-Zehnder spectrum analyzer. Methods for experimentally determining the complex mutual coherence function of the illumination using the analyzer are also described. The addition to the system of a calibrated phase shifter controlled by a minicomputer is proposed, which permits the spectral amplitude and phase to be determined automatically in real time.

Adaptive Resonator Control Techniques For High-Power Lasers

Abstract: An essential requirement of high-energy laser resonator configurations is the capability of efficiently extracting power in a near-diffraction limited beam. Mode discrimination as well as optical beam quality are often compromised as a result of temporarily varying refractive index perturbations within the gain medium, optical cavity misalignment, mirror figure errors resulting from manufacturing tolerances, and thermally induced mirror distortions. Various design approaches have emerged in recent years to optimize the far-field irradiance by utilizing different resonator concepts for the purpose of obtaining the best mode control and near-field beam quality. The different concepts utilize annular and compacted gain mediums, spatial filtering techniques, novel optical components and adaptive optics. This paper will describe recent results using intracavity adaptive optical techniques versus extracavity adaptive optical techniques. Experimental results will be provided which show the correction capability for controlled low order aberrations (tilt and astigmatism) commonly found in high energy lasers. A comparison of two optimization control techniques using a multidither zonal COAT system will be discussed describing the effects of hardware limitations and considerations on the performance of the system.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.