The evolution of the Sprite detector from its invention in 1974 to the present is reviewed. The use of anamorphic optics to reduce the effects of carrier diffusion, together with changes to the device shape has produced very high spatial resolution. Improved material and two-dimensional structures have further increased the thermal sensitivity. A brief description of the technology for two-dimensional, electronicaly addressed diode arrays is also given, together with a discussion of the mechanism of p to n type conversion.

The solid solution HgZnTe is an attractive material for IR photon detectors. The liquid phase epitaxy growth technique, used in our laboratory for HgZnTe, is briefly described. The characteristics of p type HgZnTe epilayers, before and post an annealing process in Hg atmosphere, are presented. The status of HgZnTe as an alternative material to HgCdTe for IR photon detectors is discussed.

The research and development status of work in monolithic as well as in hybrid IRCCD-focal plane array (FPA) detectors based on the sensor materials InSb, Cdx Hgi-x Te and Si: X (X = In, P, Ga) at the AEG Company is described. Some examples for applications in mostly civil applications are given.

One of the major application fields of image processing techniques is the 'visual inspection'. For a number of rea-sons, the automated visual inspection of Integrated Circuits (IC's) has drawn a lot of attention. : Their very strict design makes them very suitable for an automated inspection. : There is already a lot of experience in the comparable Printed Circuit Board (PCB) and mask inspection. : The mechanical handling of wafers and dice is already an established technology. : Military and medical IC's should be a 100 % failproof. : IC inspection gives a high and allinost immediate payback. In this paper we wil try to give an outline of the problems involved in IC inspection, and the algorithms and methods used to overcome these problems. We will not go into de-tail, but we will try to give a general understanding. Our attention will go to the following topics. : An overview of the inspection process, with an emphasis on the second visual inspection. : The problems encountered in IC inspection, as opposed to the comparable PCB and mask inspection. : The image acquisition devices that can be used to obtain 'inspectable' images. : A general overview of the algorithms that can be used. : A short description of the algorithms developed at the ESAT-MI2 division of the katholieke Universiteit Leuven.

The driving forces of production are: 1.increase productivity 2. reduce production cost 3. enhance quality

Characterization and control of membrane-based separation or drug delivery systems require the development of noninvasive methods for measurement of membrane hydration during the process of interest. In this paper, real time fluorescence methods which were developed in order to study such membrane systems are described, and data which demonstrate their sensitivity and speed are presented. Sensitivity and speed were sufficient that transient phenomena such as diffusion lag time and Donnan distribution effects caused by changes in fixed charge density were well resolved.

A passive optical-Hartley transform of white light scenes was performed by means of a rotational shear interferometer. The full visible band was utilised by employing a colour corrector which compensated for wave-length dependence of the fringes. This transform can be used for filtering, moment calculation, or for direct detection. An inverse transform was also realised, which allowed retrieval of the original object, although at a low efficiency.

Optical correlation schemes based on circular or radial harmonics have bean recently suggested for performing pattern recognition in presence of rotation or scale variations of the object. Those schemes however are based on using a single harmonic at one time. In this paper we are presenting two approaches that overcome this restriction.

The Bragg reflection waveguide is formed by surrounding a central waveguiding region by dielectric layers with periodic variations in refractive index. The limitations imposed by resonant confinement of the guided modes (transverse Bragg reflection) are analyzed, and the unique properties of a pair of coupled-waveguides of this type are described.

Early attempts to extend staring-mode sensing into the thermal infrared spectrum failed, because the resulting imagery was dominated by spatial pattern noise. The source of this noise was modulation of the infrared background by local variations in sensor responsivity. In 1973, use of internal photoemission from silicide Schottky barrier arrays was proposed as a means of achieving the photoresponse uniformity necessary to obtain useful thermal imaging capability. In the next two year, silicide tube and solid state imaging devices were demonstrated. Tube development was abandoned in 1975. Solid state efforts were directed towards extension of photo-response to longer wavelengths and fabrication of large scale arrays with small, high fill factor, pixels. Cut-off wavelengths have evolved from 2 μm to 10 μm and array sizes from 1 x 64 to 512 x 512 since that time. Current silicide cameras have sensitivity comparable with the best scanning systems. This paper will describe recent advances in silicide sensors and project future technology trends.

The reverse breakdown characteristics of 8-12μm Hg_1-x Cd_xTe photodiodes are experimentally measured and analyzed. Temperature dependence of the currents reveal that trap-assisted and direct band-to-band tunneling processes dominate the breakdown characteristics at low and high reverse bias regions respectively. The direct band-to-band characteristics are compared to theoretical predictions in implanted diodes on both gold-doped and undoped substrates. A good quantitative fit to theory is achieved based on experimental analysis of space charge density in the measured diodes depletion region using a C-V profiling technique. The direct tunneling characteristics also show empirical correlation with noise currents measured on gold-doped junctions.

Moire deflectometry, a method for ray deflection mapping, is described. Its use in lens testing for determining properties such as surface microstructure, radius of curvature, thickness, aberrations, and OTF (optical transfer function), is demonstrated. Unlike interferometry, moire deflectometry is a ray tracing technique, and therefore the analysis of three dimensional objects is greatly simplified. Although the ray tracing approach to optical systems is much older than wave theory, moire deflectometry seems to be the first attempt to apply ray tracing methods systematically to optical metrology. The technique is fully quantitative, interferometry compatible in accuracy, and has the additional advantage of tunable sensitivity.

A Computer Generated Hologram (CGH) is used as an aberration corrector in construction optics to record Holographic Optics Elements (HOE's) with preaberrated wave-fronts. In the system described, the CGH provides enough asphericity to record the re-quired HOE, so that other lenses in the construction optics can be selected by paraxial considerations alone. The design process of the recording system is described and a comparison is made between the measured and expected performance of the final lens.

New and simplified processing procedures and formulations for Silver Halide Sensitized Gelatin (SHSG) holograms of high diffraction efficiencies and signal to noise ratios are presented. holographic performance of SHSG was found to be far superiour when compared to reversal bleach experiments. Additional improvements in diffraction efficiency and scattering noise were achieved by introducing triethanolamine into the postfix soaking bath at elevated temper-atures. Finally, a holographic focussing lens with low aberrations was realized in SHSG.

The standard single-target acquisition model used in military applications for human target acquisition using infrared systems has been extended to the multitarget scenario. It incorporates three possible versions depending on the underlying causes for the non-unity detection probability at infinite time and the degree of correlation between targets.

Thermal images of natural terrain in the long wavelength infrared (LWIR) are due to thermal emittion of the ground. On the other hand in the short wavelength infrared (SWIR) images there is a contribution of direct sun light due to reflection. The daily evolution of the terrain thermal images with the same thermal properties in both spectral windows were performed using an IR imaging radiometer. The sun reflection and the thermal emmition will affect the correlation between the images. Measurements have shown that the cross correlation goes through a maxima and a minima depending on the sun angle. It seems that the maxima point occurs when the shadow effects are minimal.

Modes of vibration in rectangular, orthotropic, free-free plates are determined optically, using an electronic speckle pattern interferometer (an instrument called the VibraVision) as real time instrument and a double pulsed ruby laser to record the corresponding holographic interferograms. It is found that the first three modes of vibration has a strong dependence only of one of the main material parameters at a time, namely in plane shear modulus and the two Young's moduli, respectively. It is therefore a simple task to determine these material parameters with this nondestructive, noncontact optical method. Poisson contraction ratios are harder to determine. One method is to tune the sides of the plate so that the second and third modes are turned into a ring-shaped and a cross-chaped mode. The Poisson contraction number has a stronger influence on these modes and can be determined. Experimental results and theory are presented.

Isotropic and non-isotropic plates are impacted by a ballistic pendulum. The bending waves that are generated are studied with holographic interferometry using a double pulsed ruby laser as light source. The pulse shape changes with time because of the dispersivity of the waves. Initially the fringe pattern in the isotropic case is cylindrically symmetric and determined from an initial value problem. Later, when the waves have reached the plate rim, in-and outgoing waves gradually develop fringe patterns which in the end will be a combination of eigenmodes of the plate. A solution to the corresponding Kirchhoff plate equation is presented, which in the special case when the impact is modelled as a Dirac-pulse in space and time, is shown to depend only of the distance to the impact point divided by the square root of the time after impact and a parameter containing plate parameters. From the slope of the central deflection material parameters can be determined. Another solution, assuming a finite inpact time, is shown to agree better with experiments. Results from investigations of non-isotropic materials are also presented.

A novel method for active laser diode stabilization is described. The input for the control loop is taken from an external common path Jamin interferometer by differential detection of the fringe pattern. Theoretical and practical limitations are discussed with experimental results indicating laser stabilization capabilities better than one part in 10⁸.

A novel design technique for generating holographic elements that perform general types of coordinate transformations is presented. The design, which is based on analytic ray-tracing techniques leads to a holographic grating function that can be formed either as a computer generated or as a computer originated hologram. The design procedure is illustrated for a specific holographic element that performs a logarithmic transformation. Such an element is useful for obtaining scale invariance in optical correlation.

Holographic optical correlators using incoherent light have been developed for pattern recognition. In this paper we show how multiplicity of holographic filters can be incorporated into such correlators for recognizing several patterns simultaneously. Our computer simulation and experimental results reveal that sixteen patterns can be recognized with one composite holographic filter, giving a sharp correlation peak with good peak to background ratio.

This work was conducted on purpose to find the feasibility of producing light weight, ligh aspect ratio mirrors for scanners, folding and head mirrors used in compact optical assemblies by the cost effective polymer replication technique. The work includes theoretical consideration, experimental results and implementation of empirical results in present used mirrors.

The results of three visual inspection techniques, using laser light, for defect detection in unexposed radiographic film are presented and compared. First convolution techniques are discussed. An appropriate choice of mask coefficients is explained and the mask dimension has to be matched with the scale at which the errors occur. Second an error detection method using polynomial regression was experienced to be very effective. Finally, fourier filtering can equally well be applied but it was computationally more expensive than the convolution method for this type of inspection. Experiments have been carried out using the LILY software package for image processing.

A high sensitivity focus sensing configuration is employed in the construction of an accurate optical profilometer. The system is analyzed theoretically and experimental investigation indicates a sensitivity better than 3nm with a linear dynamic range of 50μm. The deteriorating effects of finite apertures and various misalignments are also considered and taken into account for improved measuring procedures.

The purpose of this system (Fig. 1) is to locate accurately two pieces of fabric lying on a table. The pieces are laid down on the table with an orientation accuracy of ±12° degrees and cartezian shift up to 30 mm. The location of the two pieces is then tranfered to a robot arm that will pick them up as a matched pair and trnasfer them as such to an automatic sewing machine.

Single-mode fiber is rapidly becoming the medium of choice for lightwave communications systems carrying long distance terrestrial and submarine traffic as well as local distribution and local area networks traffic. Widespread and convenient utilization of single-mode fibers requires reliable and reasonably priced hardware such as low-loss backplane and field connectors, laser-fiber couplers, and directional couplers. The main drawback of single-mode fibers, which makes fabrication of these components difficult, is their small core size, on the order of 5-10μm. All hardware constructed from and for these fibers, where two cores or light source and core have to be aligned, are inherently very sensitive to axial and transversal displacements as well as to tiny dust particles. These displacements can be induced mechanically or thermally, while the dust comes from just routine handling.

This paper is devoted experiments with transmission of images and holograms through single multimode optical fibre. The technique is mostly promissing because of its paralellness.

A method for deriving the angular power distribution of various sources which are used to inject light into an optical fiber is suggested. This distribution can be obtained from the optical power carried by meridional bound rays in a fiber whose cladding refractive index can be modified. The theoretical analysis, which indicates that optical power measurement errors must not exceed 1% in order to obtain reasonably accurate power distributions, is augmented by experimental results. In particular, the case of lens illumination and the estimation of the mode field diameter of a single mode fiber are studied in detail.

Chalcogenide glass fibers, transparent in the mid IR region, will soon find a wide range of applications, including military uses such as thermal imaging, sensing and tracking, and remote spectroscopy. We have developed chalcogenide glasses and optical fibers and bundles suitable for such military applications. Herein we describe the As₂Se₃ chalcogenide fibers and bundles with glassy core and TFE cladding, with a fiber diameter of 30-1000 μm. The optical loss, measured by CO₂ laser and FTIR spectrometer in thee temperature range of -197'C to 100'C, is less than 1 dB/m in the 3-5 μm range and less than 10 dB/m at 10.6 μm. At longer wavelengths the attenuation is much higher. The fibers maintain their transparency in the temperature range of -40*C to 70'C (military standard range).

Optical properties of hollow-core, chalcogenide glass cladding fibers, which are good candidates for power transmission, were examined. Far-field patterns - as a function of excitation conditions - of the emitted radiation of As₂Se₃ hollow core fibers, at 10.6 μm, are described. Results are preceded by a theoretical background. Hollow core fibers are found to guide only a small number of modes.

Hollow plastic fibers were produced by depositing metallic and dielectric films on the internal surface of plastic tubes. These fibers can transmit high CO₂ laser energy with low atten-uation even in curved trajectories. A mathematical model was developed to describe the energy transmission. The energy distribution at the outlet of the fiber was measured and found to be influenced by the existence of whispering gallery mode. These fibers are suitable for surgical uses.

There is an increased demand for high quality optical components with minimal surface roughness for precision optical systems. As a result, it has become necessary to determine the surface quality using an accurate, quantitative and non-destructive measurement. This has led to considerable efforts to replace stylus methods with non-contact optical methods for surface texture measurements. Several non-contact optical methods have been tried and some of these have been implemented in commercial instruments. One of these methods utilizes the principle of differential interference con-trast. The system theory and implementation are described; results and calculations are presented for polished surfaces.

We describe here a system for measuring very accurately diamond-turned surfaces. This system is based on heterodyne interfercmetry and measures surface height variations with an accuracy of 4A, and the spatial resolution is 1 micrometer. Fran the measured data we have calculated the statistical properties of the surface - enabling us to identify the spatial frequencies caused by the vibrations of the diamond - turning machine and the measuring machine as well as the frequency of the grid.

Laser based techniques for the generation and the detection of ultrasonic surface waves (SAW) are described. These methods were motivated by practical ultrasonic non-destructive testing (NDT) applications and are suitable for operation on rough surfaces which are typical to engineering materials. Wide strip laser illumination is used to generate SAW waveforms by means of a thermoelastic mechanism. For detection an holographic method has been developed, achieving sensitivities of the order of 0.1 Å at 10 MHz bandwidth on rough aluminum surfaces.

A simple third order analytical solution is presented for a design of a reflective beam expander using a spherical primary, parabolic secondary and an aspheric corrector plate. The third order design is also evaluated and improved by a ray trace program.

Due to the progress of the diamond turning technique, the use of aspheric elements in optical systems is increasing. However, there are materials, like glass, which are not compatible with this technique especially when the shape of the aspheric element is not a simple conic. Using ion beam milling through a mask which modulates spatially the amount of ions impinging on the surface to be shaped, a piano-convex glass lens has been transformed into an aspheric element with a conical front surface. This technique is valuable for any material used either in the visible or in the IR spectrum.

High accuracy optical alignment generally requires interferometric methods. A simple computer aided interferometric optical alignment procedure, for the visible, IR and other regions, utilizing the Interferogram Interface in CODE V, is described. The accuracy of visual interferometric alignment is limited and involves highly skilled personnel. To overcome these limitations, a procedure is presented that requires specification of the nominal optical system design, the alignment parameters, such as tilts and decenters in CODE V, and entering in to the latter the interferometrically measured system wavefront data of several different points in the field of view. The last step consists of predicting the alignment parameters such that the system wavefront error is reduced. This procedure is repeated until the wavefront error falls within system specifications. A numerical alignment simulation and an actual system alignment are presented for an F/10, 8 inch diameter Cassegrain objective.

During seeing the eye scanns incessantly over the inspecting scene. These eye movements represent an automatic process, consisting of two phases: proper saccadic movements and fixation period during which two processes take place. These are sampling the scene and processing the visual information by the central part of the retina and next by corresponding structures of the brain. At the beginning the fixation points are randomly distributed but with time these are grouped round peculiar parts of the scene. The movements are unavoided: When the eye steps for a tine the visual perception disappeares, the subject dont see anything.

Infrared imaging sensors are characterized by extended dynamic ranges ≈ 60db due to target and background variations and increased senstivity of the sensors. The dynamic range of display devices such as video monitors is limited to approximately ≈ 40db, requiring in turn appropriate means for compression. Various compression schemes have been proposed based on the compression of the low spatial-frequency components of the image signal, while preserving (or enhancing) the high frequency signal components. The separation of low and high frequency components using various spatial filtering techniques is limited by (i) attenuation and extinction of low contrast and extended targets, and (ii) compressed signal distortions and "ringing" effects around edges. We propose an adaptive, spatial filtering scheme which largely overcomes these limitations while retaining the subjective quality of the compressed image. The adaptive nature of the operator may be tailored to expected target dimensions (in pixels), and to expected target and background contrasts.

Successive digitized measurements of constant data fluctuate over several quantum cells because of the presence of additive noise. This dispersion allows the achievement of a subquantum accuracy by signal averaging of a large number of measurements. This processing is of particular interest for infra-red signals, characterized by a wide dynamic range. This work analyses the relation between the expectation of the digital measurement and the expectation of the real (analog) value, as a function of the statistical characteristics of the noise in the signal. It is shown that sub-quantum precision can be obtained under certain conditions. Practical considerations regarding the achievable accuracy, digitization depth, measuring the noise statistics and limits of the linear subquantum interpolation are given. A practical method for measuring noise in the signal is described.

Image processing, in general, and image enhancement in particular, have been active topics for over 25 years, and much is known about them. However, it appears that quantitative measures for image enhancement, as such, have not been formulated, even though the theory necessary for such a measure has been developed. Such a measure will be presented and applied to a representative form of image enhancement. Simple enlargement may serve as a good illustration. Such phenomena as image degradation due to excessive magnification, which are well known qualitatively, are put on a quantitative basis.

In all types of solar collectors without exception, there is a protective cover between the sun rays and the active area (thermal or photovoltaic, flat or concentrating collector). For the materials most often employed the refractive index has a value around 1.5 leading to about 4% loss by reflection for each air-cover interface, giving a total loss of about 8% of the incident energy.

On total internal reflection (TIR) different phase shifts occur to the p- and s- states of polarization. Therefore the polarization state of the reflected light on TIR is generally elliptical polarized and differs from the state of polarization of the incoming wave. Only in cases where the entering wave has a pure p-or s- state relative to the plane of incidence these polarization states of the reflected wave are unchanged and hence are eigen-states. In optical systems where the optical path is folded via TIR by using prisms, corner-cubes, retro-prisms, etc., the state of polarization of the exit wave will usually differ from the incoming one. In cases where the polarization state should be conserved, correcting retardation elements are applied to compensate the polarization effects on TIR. Instead of these bulk correcting elements, multilayer dielectric thin films stacks could be applied on the desired surfaces. This technique is introduced and discussed. An illustration of this method is represented on a retro - roof - prism of the type 45°-60° -60°.

A network calculus suitable for the modeling of optical networks is presented. The new calculus is based on the signal flow graph theory which is used for the modeling of electrical and microwave networks. The new element in the optical network calculus is the fact that the nodal variables and the branch transmissions are two dimensional vectors and matrices respectively, rather than complex numbers. The new calculus is applied to a simple optical network as an example.

The design of efficient, wide-angle, dielectric optical waveguide junction splitters with two, or more, branches is outlined. The method has several degrees of freedom which can be used to optimize the device's performance to achieve: 1) Minimization of the radiation loss for a specified mode at the input, 2) Equalization of the modal losses in a dual-mode device, and 3) Controllable power splitting ratio in a multibranch splitter.

Commercial tunable polarization maintaining fiber couplers exhibit inadequate low polarization isolations. Utilizing a newly developed coupled mode theory, we theoretically analyze the performance of these devices, and conclude that these low values can be explained in terms of finite misalignments of few degrees between the two fibers' principal birefringent axes. We also show that for a given device with 3dB coupling ratio the polarization isolation critically depends on the transverse setting, and can vary between 18 and 40dB for the case of 5° misalignment, in a coupler composed of 3mm beatlength fibers.

By mounting the IR detector on the cooler cold finger a significant reduction in the total heat load can be achieved. This approach is a specially fruitful when the ratio of detector heat load/dewar parasitic heat load is relatively low. Such a package which is sold under the trade name LILIT is in regular production by Ricor Ltd. Israel since 1987. This packaged system weighing about 430 grams, consumes about 5...8 W input power to maintain 80 K under 50 mW heat load. The basic design concept, typical performance data, qualification status and some typical applications are presented.

The need for microlenses with a wide-range of focal lengths from 10μ to 100mm and with a diameter varying from 10μ to 1mm lead to the development of various techniques which are able to generate these lenses in a photoresist substrate. The existing techniques are reviewed and a new one proposed. In this technique a positive or negative photoresist layer is exposed to a tailored light intensity distribution. After development of the photoresist, its surface is identical to the spatial intensity light distribution. Photoresist with an index of refraction of n=1.6 in the visible spectrum, can be used as a lens.

Simple centroiding, cross-correlation and triple correlation techniques have been applied to the imaging of randomly translating and rotating objects at very low light levels. The results of a computer simulation show that satisfactory reconstructions can be obtained using the cross-correlation technique at photon levels on the order of 0.2 photons per pixel for pure random translation or rotation, and on the order of 0.5 photons per pixel for both random translation and rotation, with only a few hundred frames in each case.

We have obtained diffraction-limited astronomical images utilising a variant of the shift-and-add method. We show that the matched filter approach for extending the weighted-shift-and-add method does indeed reduce specklegrams from extended objects and one dominated by photon noise. The method is abberation-insensitive and yields very high dynamic range results. The iterative method for arriving at the matched filter does not automatically converge in the case of photon-noisy specklegrams for objects with more than one maximum. Methods for making the procedure more "artificially intelligent" are discussed.

If we compare rotational shear interferometry to standard speckle interferometry we find that it is easier in the first case to separate the atmospheric phases from the object transform phases. Phase closure and blind deconvolution should be directly applicable. Laboratory simulations were conducted to verify theoretical predictions and computer simulations for the phase closure case, and preliminary results show promise.

The Solar Blind Ultraviolet (SBUV) spectral region covers the interval between 230 nm and 290 nm. The lower limit of this interval is given by the edge of the Schumann-Runge band and the upper limit is determined by solar radiation penetrating the stratospheric ozone shield. The SBUV region is interesting from the experimental point of view, since the lack of solar background is favorable in such applications as lidar, atmospheric communication and remote sensing. The present models (LOWTRAN-6) include as atmospheric attenuators in this region ozone absorption, aerosol and molecular scattering. New theoretical calculations of the Herzberg I oxygen band predict significant absorption by 0₂. This prediction is confirmed experimentally in the present study. Field measurements at 252, 255 and 264 nm are reported over optical paths of up to 2750 m. Results show that LOWTRAN-6 is inadequate in the SBUV region, as indicated by the present extinction measurements.

IR transmission spectra of 1n₂0₃ microcrystals and thin films in the range 300 - 700 cm^-1 were studied. Results on band shifts support the idea that bands in microcrystals spectra correspond to surface polaritons. Anomalous clumping effects and different behavior with respect to charge carrier localization at low and high frequency bands are presented.

We apply a recently developed model for non-radiative energy transfer in correlated systems to recently published data on energy transfer in garnets. We show that even in well-studied materials in which the analysis of the data appears straight forward, subtle deviations from theory and difficulty in quantitatively evaluating interaction parameters may be due to a non-random distribution of donors and acceptors in the crystal.

The structure - properties relationship of large-grain poly-crystalline and single crystalline optical germanium, was compared in terms of electrical and optical properties. The dopant distribution and the optical properties relevant to thermal imaging showed better homogeneity of the single crystalline than the polycrystalline material.

We have investigated all-optical modulators in gallium arsenide integrated optical waveguides; these modulators use electron-hole pair generation to alter the propagation characteristics of a guided light beam.

For Low Light Level E/O systems, the Air Light may give the major part of a signal, but will reduce the possible resolution. Photographic envelope, defined for different imaging systems applications, must include such effects. The scattering and absorption of sunlight by atmospheric aerosols, molecules and ozone affects the quality of images and is usually described in terms of a Multiple Scattered Radiation. Such radiation, responsible for creating Air Light, is a complicated physical and computational problem, that sometimes gives very untrivial results. This paper reviews the atmospheric path radiance Air Light as a part of a system approach to E/O systems. We present the algorithm for calculation of many stage scattering processes and suggest a non sophisticated criterion for its importance.