Abstract: A new type of holographic optical element combines some of the flexibility of computer-generated holograms with the high light efficiency of volume phase holograms to produce optical elements capable of arbitrary illumination transformations with nearly 100% light efficiency. The optical element is recorded by subdividing a volume hologram film surface into numerous small areas (facets), each of which is individually exposed. A final optical system consisting of two dichromated gelatin holograms in series is demonstrated. The first hologram spatially redistributes the incident light, and the second hologram produces a desired phase front on the redistributed light.

Abstract: Scanning beam microwave radars were used to measure ocean wave directional spectra from satellites. In principle, surface wave spectral resolution in wave number can be obtained using either short pulse (SP) or dual frequency (DF) techniques; in either case, directional resolution obtains naturally as a consequence of a Bragg-like wave front matching. A four frequency moment characterization of backscatter from the near vertical using physical optics in the high frequency limit was applied to an analysis of the SP and DF measurement techniques. The intrinsic electromagnetic modulation spectrum was to the first order in wave steepness proportional to the large wave directional slope spectrum. Harmonic distortion was small and was a minimum near 10 deg incidence. NonGaussian wave statistics can have an effect comparable to that in the second order of scattering from a normally distributed sea surface. The SP technique is superior to the DF technique in terms of measurement signal to noise ratio and contrast ratio.

Abstract: An analysis is made of some characteristics of the formation of a Stokes wave in stimulated Brillouin scattering (STBS) both from the spontaneous noise and under conditions of amplification of a signal correlated with the pump wave. This analysis is used to develop a technique whereby efficient reflection of a laser wave with wavefront reversal can be obtained using a light pipe of arbitrary transverse dimensions. Experiments carried out using a prototype nine-channel laser facility showed that by using an STBS oscillator–STBS amplifier system, it is possible to increase the reflection coefficient and improve the reversal quality, so that this system has advantages for the development of high-power multichannel laser systems.

Abstract: High sensitivity height and phase contouring is achieved by the superposition of a wave front with its complex conjugate. Phase conjugation is obtained by reconstruction of Fourier transform holograms with the help of various optical systems. The mathematical procedure uses a novel operator algebra that simplifies calculations.

Abstract: A complex optical system may be aligned by means of a technique in which an analytical model of the system is utilized which is assumed to be capable of essentially optimal performance. A physical example of the same system design is then assembled and a plurality of performance characteristics measured. A plurality of specific adjustments are then calculated which would have the effect of degrading the performance of the analytical model to equal that measured for the physical example, whereupon compensating physical adjustments are made to the physical example. For many applications, the performance measurements may relate to aberrations to the wavefront of the point source image quantified by means of a Hartmann mask or the like. In that event, the estimation technique may be a straight-forward linear approximation technique including possible damping and/or weighting factors. The performance measurements may also be related to the intensity function associated with the image of a point source, in which case a second order estimation technique is required.

Abstract: First a transmission-type optical element, which modulates the phase of the incident wave field in a 1-D manner, is proposed, then several such elements are combined in a cascade to construct an adaptive transmission-type 2-D phase modulator. The element consists of a deformable glass plate made by bonding an appropriately shaped PVDF piezoelectric film with transparent electrodes to a laminar glass plate, a plane glass plate, and a medium immersed between the two plates. The construction of the modulator, complementary methods to improve the characteristics, several basic experimental results, and its use to compensate for aberrations in an imaging system are given. The modulator constructed can generate wave fronts whose phase profile is expressed by the functional form ax(2) + by(2) + cxy.

Abstract: An analysis of wavefront reversal (WFR) of optical beams in anisotropic media (class 3m electrooptic crystals, such as LiNbO3 and LiTaO3) is used to show that WFR depends strongly on the crystal orientation and on the predominant nonlinearity mechanism. A new type of WFR of parallel beams is proposed, this being due to intermode scattering between ordinary and extraordinary waves in holographic gratings.

Abstract: The speckle transfer function 〈T(α1)T*(α2)〉 has been analyzed as a function of the strength of the atmospheric turbulence, of the shape of the wave-front correlation function, and of the lower-order deterministic aberrations. The speckle transfer function is shown to be highly dependent on the width of the wave-front correlation function. The effects of symmetric aberrations (e.g., defocus and spherical aberration) and asymmetric aberrations (e.g., coma) in the exit pupil of the telescope have been calculated for 〈|T(α)|2〉, the transfer function of Labeyrie speckle interferometry, and for 〈T(α)T*(α + β)〉, the transfer function of the Knox–Thompson phase-recovery algorithm.

Abstract: A novel type of neutron interferometer was constructed and tested employing a split cylindrical zone plate with neutrons of 20 A wavelength Its performance and relative merits are discussed

Abstract: An acoustic wave source and a radio wave source are installed close to each other on the ground. When an acoustic wave pulse is transmitted vertically into the atmosphere by the acoustic wave source, spherical wavefronts formed in the atmosphere by the acoustic wave are propagated upwardly at the velocity of sound. When a continuous radio wave is transmitted from the radio wave source toward the spherical wavefronts, it is reflected by the wavefronts and the reflected radio waves are converged to form a focusing spot on the ground. The position where the spot due to the convergence of the reflected radio waves is formed with the maximum intensity is detected by means of an antenna network formed of a multiplicity of receiving antennas laid out in the pattern of a lattice. The time-course change of such positions of the spots is traced to realize remote measurement of the height distribution of wind direction and speed in the atmosphere under surveillance.

Abstract: In this paper, we have reprocessed a set of previously published intensity coherence time data to correct for wave front curvature. The spherical wave correction decreases the coherence time for a simple plane wave. Under conditions of strong scatter, theory predicts a simple power law relationship between the intensity coherence time and the phase turbulent strength. In the theory the power law index is simply related to the phase spectral index, which is usually assumed to be constant. Previously, this theory had been applied to test the consistency of the results. Evidence has recently come to light, however, that both the phase and in situ spectral indices vary systematically with changing perturbation strength. By accommodating this variation as well as the wave front curvature correction, we were able to greatly improve the theoretical fit to the intensity coherence time data.

Abstract: The disclosure illustrates a wave front sensing device of the Hartman sensor type in which a number of concentric toroidal surfaces machined in a single substrate reflect light into a series of corresponding ring foci which foci impinge on an array of linear optical detectors.

Abstract: The problem of wavefront reversal in stimulated Brillouin backscattering in a pump field with onedimensional transverse modulation for the reversing mode of the scattered field is considered. Calculations are made of corrections corresponding to "serpentine" distortions. The fraction of these distortions is ~xln(1/x), where x =g/kθ2 is the product of the gain g (in reciprocal centimeters) and of the Fresnel length (kθ)−1 of a pump field with the divergence θ. Specific differences between the one-dimensional and twodimensional problems are discussed.

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.

Abstract: A parametric phase-reversing amplifier of sound is described. Its operating principles and estimates of the parameters are given. An actual amplifier is described: its active medium is a liquid containing gas bubbles and it is pumped by an alternating electric field. The phenomenon of two-pulse electroacoustic echo is analyzed from the point of view of parametric reversal of acoustic wavefronts.

Abstract: A wavefront sensor for detecting the slope of an input wavefront. A surface acoustic wave reflective diffraction grating is positioned at a focal point of the wavefront, and generates surface acoustic waves at two primary frequencies f1 and f2. The reflective diffraction grating produces a first AC shearing interferogram between two like diffraction orders generated by the f1 and f2 surface acoustic waves. A photodetector array is positioned to detect the shearing interferogram at a two dimensional array of zones, and the phase of the output signal for each zone is representative of the local slope of the wavefront in the direction of shearing, thus producing the slope in one direction. Complete two dimensional wavefront slope information is obtained by shearing the wavefront in a second orthogonal direction in substantially the same manner utilizing a second surface acoustic wave diffraction grating and a second photodetector array.

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.

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.

Abstract: The present invention relates to a phased array antenna system which, in the transmission mode, forms a directional planar wavefront (20) including a signal at a first frequency at a first array (18 1 -18 m ) which is a sub-multiple of the frequency to be ultimately transmitted. By sending the wavefront through a lens or reflector, an image of the first array is formed on an image plane. A second array (26 1 -26 n ) disposed at the image plane intercepts the wavefront and the received signal's frequency and phase is then harmonically multiplied by a predetermined number to permit reradiation of the resultant signal by a third array (32 1 -32 n ) in the same direction as the original wavefront. The second and third arrays include corresponding elements and configurations with more elements than the first array. In the receive mode, the sequence is complementary to the transmit mode.

Abstract: A ray method is used to calculate the near-field ground acceleration excited by sliding on a fault plane. The sliding action is modeled by a propagating mode II crack. The crack is planar and it has an edge of arbitrary but smooth curvature. Attention is focused upon the case in which the expanding crack abruptly changes its rate of growth to a slower one. This change in propagation speed causes a burst of wave motion to be emitted. The interaction of the high-frequency (or wave front) part of the emitted acceleration pulse with the free surface is studied. The near field, where body waves dominate the wave motion at the surface, is considered in some detail.

Abstract: A review is given of results obtained by the present authors in investigations of wavefront reversal in degenerate parametric processes. An analysis is made of the problem of transmission of signal radiation along an optically inhomogeneous path. A model of a system to compensate for phase distortions using wavefront reversal in parametric processes is developed. The mathematical device of the spread function is used to determine the limiting capabilities of the method. It is found that satisfactory compensation for distortions is achieved when a parametric radiation converter resolves the effective scale of the inhomogeneities. The possibilities for implementing these systems in practice are discussed.

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.

Abstract: Resonant wavefront reversal was observed in the active medium of a copper vapor laser employing the four-wave mixing configuration. The power reflection coefficient was 100%. The process of reversal occurred when the average power of the interacting beams was of the order of tens of milliwatts.

Abstract: A numerical analysis is made of the dependence of thermal defocusing of the output beam in a CO2 amplifier on the parameters of the input radiation pulse. It is found that defocusing is appreciable when the pulse duration is comparable with the time needed for equalization of the gas pressure over the cross section of the beam. The Hamiltonian formalism is used to describe the quality of the output beam. It is shown that wavefront reversal of the beam can be used to suppress this type of defocusing in amplifiers.

Abstract: This paper describes the digital retrieval method of the wave aberration of an optical system from the point spread function or the optical transfer function data of the system. The Gerchberg-Saxton algorithm is used as the iterative retrieval technique of the wave aberration with additional information about the type of aberration. The usefulness of the proposed method is confirmed by computer simulations. Several problems associated with the retrieval procedure are indicated by elementary experiments with a computer generated hologram as well as by computer simulations.