A recent development in the theory of bilateral symmetrical optical systems is applied to design the remarkable two-mirror, unobstructed Schwarzschild telescope. We illustrate how this development was used to simplify the fabrication and testing of such a system.

This paper presents a qualitative and quantitative analysis of timeaveraged projection moire vibration measurements for a plate and a cylindrical shell. It is pointed out that although moire fringes are generally considered to represent a constant contour difference or constant vibration level, in practice, variations in local grid pitch values on the test-item surface result in wide variations in measured displacement levels for given fringe numbers, which must be taken into consideration for quantitative evaluation.

Colorencoding of depth is shown to occur naturally in holograms that are reconstructed under white light illumination. It can be registered in a common color photograph, allowing a simple method of visual decoding by means of ordinary colored 3-D spectacles. The fundamental holographic equations and the photographic procedure required for maximum fidelity in threedimensional reproduction are described. The result is a new kind of photograph that shows all of the views of the object in a continuous sequence. It permits an animated photographic representation and also makes it possible to adjust the degree of depth visualization when observed as a stereoscopic representation.

Color encoding of depth is shown to occur naturally in images of objects observed through diffraction gratings under common white light illumination. A synthetic image is then obtained from a single point of view, a phenomenon that can be applied to stereophotography. The image can be recorded in a common color photograph, providing a simple method of visual decoding by means of ordinary colored 3-D spectacles. The fundamental equations and the photographic procedure for maximum fidelity in three dimensional reproduction are described. The result is a photograph that has the capability of registering all of the views of an object in a continuous sequence, which is called holophotography and was previously obtained by means of a hologram. By eliminating the need for a laser and holographic film, a new technique for holography in white light is foreseen.

The inappropriate processing and digitization of an optical hologram to become a digital hologram can be modeled by additive noise superimposed on the hologram and followed by a clipping operator. Direct reconstruction of this noisy digital hologram will usually yield unsatisfactory results because the noise will be the dominating term on the reconstruction plane. The constrained iterative twin image elimination algorithm for an in-line Fresnel hologram is modified by incorporating the noise constraint into the hologram constraint domain to estimate the additive noise function while eliminating the twin image. The result of the object reconstruction is shown to be improved.

Images obtained with coherent sensors are corrupted with spots of varying gray level values called speckle noise. Recently, there has been much interest in the problem of enhancing speckled imagery, especially in the fields of synthetic aperture radar and coherent laser radar processing. This paper surveys the various methods that have been suggested for speckle removal and presents a perspective on their applicability and shortcomings. New experimental results are included.

We propose a simple method of determining whether an unknown object is a member of a class of objects. We modify the standard 4f optical correlator by inserting an amplitude mask in front of the phaseonly filter (POF) in the Fourier transform plane. Our computer simulations show that this changes the output from a POF correlation response to a classical matched filter (CMF) response. The CMF is less sensitive to an exact pattern match than the POF, which can be an advantage in detecting a class of objects. We took the Fourier transform of an ensemble average of five similar input images to make the amplitude mask, thus creating an average amplitude matched filter (AAMF). The AAMF emulated the response ofthe CMF in all autocorrelation and cross-correlation simulations. We also simulated binary phase-only versions of the CMF and AAMF. Again, in all cases the binary AAMF (BAMF) emulated the correlation response of the binary CMF (BCMF). A binary POF contains both a correlation and a convolution component. In the correlation plane, the correlation response of the binary POF is much larger than the convolution response. Both the BCMF and the BAMF correlation response contain a marked convolution as well as correlation response. The amplitude function forces more energy into the convolution response. The result is that the convolution component of the output is nearly as large as the correlation component.

A theoretical background for producing a diffraction grating with line density of 3200 lines/mm for moire interferometry is presented. The utility of this analysis is then demonstrated by producing a 3200 lines/mm grating on a three-point bend beam with an argon ion laser. The possibility of using this procedure with an invisible light source to generate a moire diffraction grating of higher line density is noted.

An improved optical method has been developed to determine the free spectral range (FSR) and spacing of Fabry-Perot interferometers (FPIs), based on accurately reproducible measurements of the absolute frequencies of FPI transmission maxima using a tunable cw dye laser and a lam bdameter. The method may be of interest for applications when the FSR of an FPI must be determined with very high accuracy, e.g., in cases of low finesse FPIs or high finesse temperature-stabilized confocal etalons, which provide frequency marks in laser spectroscopic experiments.

Studies on low power optical phase conjugation (OPC) in three saturable dyes, viz., eosin, erythrosin B, and rose bengal, embedded in two polymer films, viz., gelatin and polyvinyl alcohol, are presented. Experiments are performed using the 514.5 nm line of an argon-ion laser. Saturation intensities are determined from the transmission versus intensity plots, and triplet lifetimes are estimated from the phosphorescence decay curves. OPC experiments are performed, and the variation of OPC reflectivity with intensity and absorption length is studied. Experimental results are compared with the theory of degenerate four-wave mixing in absorbing media proposed by R. L. Abrams and R. C. Lind [Opt. Lett. 2(4), 94 (1 978)]. There is fair agreement between the theory and the experimental observations. The limitations in using these films for cw OPC applications are briefly discussed.

The real-time neutron radiography facility at the University of Virginia has been used for both transmission radiography and computed tomography. Recently, a coded aperture system has been developed to permit the extraction of three-dimensional information from a low intensity field of radiation scattered by an extended object. A technique was developed to permit retrieval of information by decoding two-dimensional coded aperture images collected with a real-time video system. An RCA video camera and a DEC PDP-1 1 computer in a network with a Convex-i parallel processing mainframe were employed. This system coupled with theoretical extensions and improvements allowed retrieval of information unobtainable by earlier optical methods. The effects of thermal noise, shot noise, and aperture related artifacts were examined so that better digital filtering techniques could be constructed and implemented. The application and advantages of this imaging technique to the field of thermal neutron imaging are discussed.

A review of photodetector arrays and architectures is presented for acousto-optical (AO) signal processing applications, for which the demands on photodetector arrays are substantially greater than for image sensing applications. The primary design considerations for obtaining photodetector arrays with high dynamic range, high sensitivity, high speed, and low crosstalk are discussed. The current status and future needs for detector arrays for AO signal processing are presented. Several novel detector structures and concepts that have potential for future AO optical signal processing use are described.

Digital simulation is needed for the analysis of the detector signal produced in an optical tracking system by a frequency modulation (FM) reticle that manipulates a target image of any possible shape By introducing a model in which the image spot is divided into arcuate strips, we develop a system of matrix operations for the digital simulation of the detector signal. By applying this method to examples of various spot shapes, such as disk and coma, we show its capabilityfor handling the digital simulation of FM reticles operated in connection with arbitrarily shaped images.

In this paper, corrected image-height targets are proportional to the field angles, replacing targets that were proportional to the tangents of the field angles. The result is better image quality.