We developed the concept of two-stage optics in 1984 under the Jet Propulsion Laboratory's 20-m Large Deployable Telescope (LDR) program to enhance the performance, lower the cost, and increase the reliability of LDR. It permitted the large primary mirror to remain as deployed or as space-assembled, with phasing and subsequent control of the system done by a small, fully assembled optical active element placed at an exit pupil. The performance and tolerances of such a system were explored. A two-stage optics testbed was constructed that successfully demonstrated the concept. Extension of the concept for upgrading the perlormance of other large, low-cost, wide-field, space optical systems was explored. An opportunity to utilize this concept arose when the problems with the Hubble Space Telescope (HST) were discovered. Its advantages for use in future very large space telescopes are addressed.

Edge effects for small deformable mirrors (DMs) with few actuators are analyzed by a matrix perturbation approach. An approximate transfer-function model is developed for spatial-frequency analysis of DMs, which includes edge effects.

Two parallel laser beams are used to align an off-axis parabolic mirror without alignment telescope and reference flat. In this method the optical axis of an off-axis parabolic mirror is made parallel to the incident laser beams, in the plane of incidence, by measuring directions of the reflected beams and by changing height and orientation of the mirror. Then, the focal point ofthe off-axis parabolic mirror is automatically found where the two reflected beams cross each other. The alignment of the optical axis to the incident beams is done without knowing focal length and off-axis distance of the mirror. Alignment sensitivity is derived both numerically and analytically. When focal length is 457 mm, off-axis distance is 127 mm, and diameter is 178 mm, the off-axis parabolic mirror is aligned to the incident beams with an angular error of less than 3 mrad.

Experimental particle size distributions of coastal fogs provided by other authors at three different visibilities have been fitted to a linear combination of three log-normal functions. With the parameters (modal radius, log-deviation, and amplitude) of the resulting functions, and using the visibility as the independent variable, interpolation polynomials have been derived to provide distribution functions at any visibility in between. To extrapolate the model to higher visibilities, an additional log-normal mode and an additional variable (the relative humidity) are introduced, so that the distribution function smoothly matches a maritime haze model for increasing visibilities. By means of Mie scattering calculations, the optical attenuation at any wavelength is calculated by the model under any visibility induced by a coastal fog. The attenuation in the visible region is compared with the input visibility and the polydispersion modified accordingly to provide self-consistency to the model.

An all solid-state 1280 x 1024 laser raster scanner (LRS) system conforming to the EIA RS-343 television standard with a limiting resolution of 1300 TV lines has been developed. The laser scanner incorporates acousto-optic devices to perform video modulation and X-Y deflection and is used in a time-multiplexed mode to photoactivate three liquid crystal light valves to project full-color, video-rate, large-screen images. Analysis ofthe LRS optical system, projection optics, electronics, and light valve characteristics is presented.

A hybrid electronic fiber optic true time-delay steering architecture is presented which retains the highly hardware compressive property of an earlier all-optical approach and introduces the economical advantages of electronics at every level possible without compromising overall performance. The architecture is particularly suited to large arrays where maximum advantage can be taken of the hardware compression. A detailed design based on this architecture is described for steering a linear, 16-element, L-band (0.7- to 1.4-GHz) array in transmit mode over a scan angle of ±20 deg with a delay resolution of 6 bits (0.63 deg). An analysis of the expected performance of the design is given together with progress toward the fabrication of the prototype system, which includes the first iteration electronic binary delay line subsystem and a single-segment, high-fidelity, directly modulated DFB laser diode fiber optic link. The experimental data from these modules is in agreement with the performance predicted from the analysis.

A wavelength-multiplexed fiber optic link architecture has been designed for transmitting ri signals with wide instantaneous band width and LO signals at microwave frequencies over long distances. The architecture involves downconverting the input rf signal, directly amplitude modulating a laser diode, transmitting the resulting rf-modulated optical carrier through single-mode fiber, and subsequently up-converting the recovered rf signal to the original band. Wavelength division multiplexing and demultiplexing is used to transmit the local oscillator signal (required for down- and up-conversions) from the transmitter to the receiver through the same fiber. By using a frequency-divided LO signal in conjunction with frequency multipliers, the wideband rf signal can be down/up-conveiled anywhere in the rf spectrum up to 100 GHz. A demonstration link has been implemented using this architecture and operates from 6.3 to 16 GHz. This link uses a 1.3-μm, 10-GHz rf bandwidth laser diode for IF transmission and a 1.55-μm, 1.5-GHz rf bandwidth laser diode for LO transmission.

A model is presented to calculate response nonuniformity in a hybrid mercury cadmium telluride focal plane array in terms of material/ device parameters. The model predicts a minimum 10% intrinsic nonuniformity contribution from the IR detector array caused by compositional variations in detector material with the state-of-the-art HgCdTe material. In hybrid FPAs an additional contribution to the nonuniformity is caused by variations in the charge injection efficiency across the area of the array. The injection nonuniformity contribution can, however, be controlled to negligibly small values by working at very high injection efficiencies, on the order of 99%.

How special reflective devices reduce the angle of incidence of a laser beam irradiating a surface with the ability to decrease the incidence angle over a wide range of angles is described. To optimize the diffraction efficiency of a focusing holographic optical element (HOE), spread of the angle of incidence of an incoming laser beam about a preferred angle should be small. There is a constraint with thick HOEs in which a Bragg effect condition must be satisfied to achieve high diffraction efficiency. Angle reduction and applications of military interest are discussed. Ways to couple a reflection angle reducer component and an HOE to a photographic or TV camera are suggested.

Maximum-likelihood range profiling is considered for pulse-dimager operation of a coherent laser radar. In particular, the expectation-maximization algorithm is used to develop a computationally simple procedure for fitting a planar surface to laser radar range data. Basic analytic properties of the algorithm are reviewed and results based on simulated and real range data are presented.

532-nm direct-detection imaging laser radar using a prototype digicon receiver was constructed and has demonstrated rapid multiple retargeting over a wide field of regard, obtaining single-shot images with intensity and three-dimensional position data for each target. Such laser radar capability is important for discrimination and targeting. The digicon receiver system obtains 8 x 8 pixel images of multiple targets at a rate of 15 Hz. Each image provides both intensity and range-to-target at each pixel. Results of experiments involving seven targets located at various distances along a 60-m light tunnel are presented. Future directions discussed are acquisition and hand-off, tracking, long-range outdoor experiments (~ 1 km), and a 16 x 16 array digicon tube with magnification.

There have been a number of methods investigated and under current investigation for monitoring the health of the Space Shuttle Main Engine (SSME). Plume emission analysis has recently emerged as a potential technique for correlating the emission characteristics with the health of an engine. To correlate the visual and spectral signatures of the plume emission with the characteristic health monitoring features of the engine, one has to acquire, store, and analyze the plume emission data in a manner similar to flame emission spectroscopy. The characteristic visual and spectral signatures ofthe elements vaporized in exhaust plume along with the features related to their temperature, pressure, and velocity can be analyzed once the images of plume emission are effectively acquired, digitized, and stored on a computer. Since the emission image varies with respect to location (the distance from the nozzle) and also with respect to time at a specified planar location, four-dimensional visual and spectral analysis needs to be performed on the plume emission data. To achieve this objective, we conducted feasibility research to digitize, store, analyze, and visualize the images of a subsonic jet in a cross flow. The jet structure was made visible using a direct injection flow visualization technique. The results of temporal (time-history-based) three-dimensional reconstruction of the cross-sectional images corresponding to a specific planar location of the jet structure are presented and the experimental setup to acquire such data is described. 3-D displays of temporal reconstructions of the jet structure are discussed.

The luminance emitted from a cathode ray rube (CRT) display is a nonlinear function (the gamma function) of the input video signal voltage. In most analog video systems, compensation for this nonlinear transfer function is implemented in the camera amplifiers. When CRT displays are used to present psychophysical stimuli in vision research, the specific display nonlinearity usually is measured and accounted for to ensure that the luminance of each pixel in the synthetic image properly represents the intended value. However, when using digital image processing, the linear analog-to-digital converters store a digital image that is nonlinearly related to the displayed or recorded image. The effect of this nonlinear transformation on a variety of image-processing applications used in visual communications is described.

In determining temperature of surfaces by their blackbody emission, simultaneous acquisition of infrared emission at different wavelengths can provide a set of parameters needed to compute the absolute temperature of the object. A graybody model can be used to derive a set of equations that correlates the effects of emissivity variation and reflection of ambient radiation on the apparent and true temperatures of the object. Such a model is presented and its sensitivities to noise are evaluated. A four-wavelength digital thermal imager has been constructed to evaluate the practical implementation of the model. Finally, utilizing a phantom that simulates a graybody, and human skin data, the validity of the model has been demonstrated. It is shown that the system noise and the computational errors of series expansion are the factors that limit the precision of the computed temperature.

Most optical setups used for accurate angle measurement have only a limited measurement range. An extension in which the total range is increased to a theoretical range of +90 to -90 deg (one-prism setup) or +60 to -60 deg (two-prism setup) with an angular resolution of 3.34 x 10^-5 deg is presented. The accuracy is also discussed.

The problems arising from nonorthonormality of the stored images in an optical resonator neural network are discussed, and a solution is given whereby the eigenmodes of the resonator can be found. This approach is implemented in computer simulations of the resonator. A number of diverse and distorted input images are successfully identified. Results for individual examples are presented and type I (in-class discrimination) and II (out-of-class discrimination) false alarm rates for this configuration are obtained. We show that by using the information on the convergence rate of an iterative scheme, the performance of the system, as compared to that of a correlation filter, can be improved.

Weighted outer product processing, which is a generalization of the bilinear transform, has applications in combinational logic design. An optical implementation of such a processor for multiple-input, multiple-data logic function operation using Texas Instruments' deformable mirror device (DMD) for real-time input is presented. The DMD, a one-dimensional spatial light modulator, allows real-time operation of such a logic function implementation by providing controllable optical encoding ofthe two input vectors that are required forthe outer product. Applications of liquid crystal television and magneto-optic spatial light modulators as real-time weighting matrices are also presented.

This paper presents a new 3-D digit-plane optical architecture for massively parallel matrix computations. This architecture decomposes matrix-structured data into digit planes using high-radix number representation and performs fast arithmetic on digit planes, exploiting spatial parallelism. While arithmetic operations are carried out using symbolic substitution, data manipulation operations (permutation, rotation, and translations) are carried out in parallel by a data manipulator using freespace optical interconnections. A new symbolic superposition technique is proposed to implement logical and set-theoretic operations on matrix-structured data in optics. The potential ofthis architecture is demonstrated to support structured matrix algebraic computation. We derive the complexity of symbolic substitution and symbolic superposition rules for radix-r arithmetic. The representational efficiency and the projected speed gain of high-radix arithmetic are compared against binary electronic matrix arithmetic.

An optical design concept is presented for a wide field of view camera, used to take pictures of a model board, which are displayed to the pilot of a simulated aircraft in real time. The concept achieves mapping functions and perspectives in three separate images that match the display system properties over 140 deg field of view. This enables fast feedback of the model board images to the pilot by avoiding the need for computer correction of optical distortion. The geometry of the lens system also ensures good uniformity of brightness over the wide field of view. The provision of three axes of angular movement and computer optical design techniques are discussed. The general design and fabrication of a prototype is described.

The architecture and experimental demonstration of a novel optical time-division multiple-access (TDMA) interconnect is presented in detail. Optical multiplexing and synchronization is used to overcome the electronic multiple-access bottlenecks associated with gigahertz-bandwidth multiprocessor communication systems. A self-clocking optical TDMA interconnect is described that may be more practical to implement than other shared-medium multiple-access protocols, such as frequency division or code division. An experimental optical TDMA interconnect is reported that uses a 100-MHz repetition rate, mode-locked laser with external modulators to generate the base-band data, and operates at a multiplexed data rate of 5 Gbits/s accommodating up to 50 channels. System measurements reveal bit error rates of less than 10^-9, low channel crosstalk, and subnanosecond multiaccess capability. A power budget analysis predicts that 100 Gbit/s systems with 1000 nodes are feasible.

Design considerations are discussed for an optical profiler consisting of an interference microscope adapted for phase shifting interferometry. The influence of several errors on the accuracy of the profiler are estimated. Specific attention is paid to the case of low-reflectance surfaces, which have to be measured with extremely high precision (e.g., uncoated bowl-feed polished glass surfaces). The accuracy-limiting factor for the measurement of these low-reflectance ultrasmooth surfaces is shown to be the inaccuracy of the measured intensity. A significant increase in accuracy is obtained by using a mercury arc lamp, which has a very high brightness, yielding a larger intensity signal and thus reducing the signal-to-noise ratio. Extensive test results of such an optical profiler using a Linnik interference microscope are presented, including the determination of the estimated reference profile accuracy. A measurement accuracy of 0.015-nm rms was obtained for uncoated glass surfaces by averaging 64 profiles. The accuracy of the estimated reference profile using 32 measurements was determined as being about 0.03-nm rms.

Novel applications of PMMA-modulator-polarizer configurations in analog optical processing are described. The PMMA system, consisting of two polarization modulators and two crossed polarizers, can perform addition as well as subtraction and multiplication. Experimental results obtained with a laboratory assembly made up of two photoelastic modulators and a pair of Glan-Thompson prisms confirm the theory. It is concluded that complex structures consisting of a multitude of programmable PMMA processors having high processing speeds can be realized by fiber and integrated optics technology.

Identification of the spatial location of images in 1-D, 2-D, or even 3-D situations is often a requirement from sampled and digitized images which refer to regular independent linearly distributed pixels. The high-precision evaluation of the position requires interpolation calculations between the spatial samples to obtain a precision better than the geometrical pitch of the elementary pixels. Two calculation methods are discussed to attain such a subpixel accuracy: The first one proceeds from the well-known method of calculating the "centroid" of the samples in the direct space; the second one relies on the retrieval of the Fourier phase frequency dependence in the frequency domain. Both specifications are evaluated and the specific case of a 3-D signal is discussed. Both methods are independent of the analytical model for the function.

Fine-structure pre-emphasis for video signal transmission exploits the three-dimensional redundancy of video signals. Companding is required in fine-structure pre-emphasis to realize SNR improvement. Fine-structure pre-emphasis is modeled as an open-loop predictive system. Analysis shows that a modulo limiter can be incorporated in the preemphasis filters to limit the peak amplitude of the pre-emphasized signal. The reduced dynamic range will alleviate stringent requirement on companding.

We have developed a magnetic-pulse-compression-type 10-kW-class solid state pulse power supply for copper vapor lasers. By triggering the gates of two gate turn-off thyristors (GTOs) connected in parallel, a 5-μs rise time primary pulse was generated. A three-stage magnetic pulse compression circuit compressed the primary pulse to 0.13 μs. The 13.7-kW GTO switching energy was achieved with a 4-kHz pulse repetition rate when a dummy load was connected instead of copper vapor laser (CVL). Total energy transfer efficiency of the power supply was 60%. This pulse power supply has been applied to a CVL with a plasma tube of 70-mm inner diameter and 1.5-m discharge length, and has operated successfully.

The temperature dependence of solar-pumped solid state lasers of Nd:YAG and two types of Nd:Cr:GSGG was studied over the temperature range of +30 to -60°C in a quasi-cw mode. All lasers had higher output powers at -40°C. The Nd:Cr:GSGG laser with a chromium concentration of 2.5 at. % produced 70 W of power at -40°C, quasi-cw. If extrapolated to true cw operation this is equivalent to 350 W. The temperature dependence of the laser performance is attributed to changes in both the stimulated emission cross section and the resonator configuration.

Wavelet transforms are powerful techniques that can decompose time series into both time and frequency components. Their application to experimental data has been hindered by the lack of a straightforward method to handle noise. A noise reduction technique, developed recently for use in wavelet cluster analysis in cosmology and astronomy, is adapted here for time-series data. Noise is filtered using control surrogate data sets generated from randomized aspects of the original time series. The method is a powerful extension of the wavelet transform that is readily applied to the detection of structure in stationary and nonstationary time series.