This PDF file contains the editorial “Editorial: Welcome to Volume 33” for OE Vol. 33 Issue 01

This PDF file contains the editorial “Guest Editorial: Infrared Technology-Part 1” for OE Vol. 33 Issue 01

The Infrared Space Observatory (ISO), a fully approved and funded project of the European Space Agency (ESA), will operate at wavelengths from 2.5 to 200 μm. The ISO will provide astronomers with a unique facility of unprecedented sensitivity for a detailed exploration of the universe ranging from objects in the solar system right out to the most distant extragalactic sources. The satellite essentially consists of a large liquid-helium cryostat, a telescope with a 60-cm-diam primary mirror, and four scientific instruments. The instrument complement is: an imaging photopolarimeter (2.5 to 200 μm), a camera (2.5 to 17 μm), a short-wavelength spectrometer (2.5 to 45 μm), and a long-wavelength spectrometer (45 to 180 μm). These instruments are being built by international consortia of scientific institutes and will be delivered to ESA for in-orbit operations. The ISO is scheduled to be launched in 1995 and will be operational for at least 18 months. In keeping with the ISO's role as an observatory, two-thirds of its observing time will be made available to the general astronomical community.

Spectroscopy is an essential tool in the astronomer's kit, probing the microscopic physics of astronomical objects. The Long-Wavelength Spectrometer (LWS) is one of two complementary spectrometers in the European Space Agency's Infrared Space Observatory (ISO). I discuss briefly the scientific considerations that drove the design of the LWS and describe the instrument itself. I then discuss how the instrument works and outline its photometric performance.

The Infrared Space Observatory (ISO) photometer is one of four instruments on board the European Space Agency ISO satellite scheduled for launch in September 1995. It covers the wavelength range 2.5 to 240 μm with wide and narrow spectral bands. Diffraction-limited observations as well as wide-beam measurements of faint extended sources are possible. Polarimetric observations can be made over the whole wavelength range. The minimal detectable flux is ~10 mJy. The astronomical areas to be addressed range from solar system objects to cosmology.

A calibration facility simulating the optical and cryogenic environment of the Infrared Space Observatory (ISO) satellite has been built for characterizing the ISO photometer (ISOPHOT). This facility uses a commercially calibrated 900-K blackbody radiation source and optics at room temperature to provide an f/15 beam to the instrument, which is contained in a LHe cryostat. The low-level infrared flux levels of the ISO are obtained by using a light-sealed instrument chamber and cold attenuation filters. The infrared flux can be calculated using the known blackbody emission and the cold calibrated transmission spectra of the filters. The calibration facility further provides a scanning mechanism, a light modulator, and filters for polarization measurements and wavelength calibrations of the ISOPHOT spectrometer channels. Electrical support equipment for the instrument operation and software for data archiving and analysis have been customized for this project. The test program comprised a standardized acceptance test for the entire instrument and special tests addressing individual instrument properties. The data obtained contain the photometric sensitivities of ISOPHOT, optimized instrument settings, reference data for the integrated system tests, and inputs for the ongoing mission planning.

A 300-element spatial radiometer was recently flown as part of the second Spatial Spectral Rocketborne Interferometer Telescope experiment. This instrument, housed in a high-off-axis-rejection telescope cooled to liquid helium temperatures, measured the spatial structure within six long-wavelength infrared spectral bands of the earthlimb. The radiometer used hybrid multiplexed focal planes with blocked impurity band detectors. The use of this technology enabled several enhancements to system performance. New data collection and analysis tools contributed significantly to the development and enhancement of this radiometer. Postflight analysis shows that the radiometer performed well during its sounding rocket flight.

Restoration of thermal images distorted by the atmosphere is presented. The method is based on atmospheric MTF analysis, both theoretical and experimental. Thermal IR atmospheric MTF measurements performed simultaneously in both atmospheric IR windows (3- to 5- and 8- to 12-μm wavelengths) are also presented. The MTFs were evaluated via point spread function measurements, under various meteorological conditions and different SNRs. Results are analyzed and shown to be in very good agreement with theoretical predictions.

A high-performance 5-μm 640 X 480 HgCdTe/CdTe/Al₂O₃ infrared focal plane array (FPA) that offers full TV-compatible resolution with excellent sensitivity at temperatures below 120 K has been developed. Mean FPA D* at 95 K and background of 10¹⁴ photons/cm² s is background-limited at ~1 x 10¹² cm Hz^1/2/W for the typical mean quantum efficiency of 60 to 70%. The key technology making this large, high-sensitivity device producible is the epitaxial growth of HgCdTe on a rugged CdTe-buffered sapphire substrate. Mean camera noise-equivalent temperature difference NEΔT of 13 mK has been achieved at ≤ 120 K operating temperature and 3.4- to 4.2-μm passband; this is about an order of magnitude better than similar currently available cameras, which use PtSi FPAs and require cooling to ≤ 77 K to maintain performance at low scene temperatures.

We have developed a 1-Mpixel infrared charge sweep device (IRCSD) imager for thermal imaging in the 3- to 5-μm band. The device of this imager is a 1040 x 1040 monolithic PtSi Schottky-barrier (SB) array using the charge sweep device (CSD) readout architecture. The pixel size is 17 x 17 μm² and the fill factor of this device is 44%. In this imager system, four video signals are read out from four independent channels on the device. The processing of these four outputs, such as sample and hold (S/H), and offset control and image correction, is performed in parallel, after which these outputs are combined to produce high-definition TV (HDTV; 1125 lines, 30 Hz) format thermal image in real time. The noise-equivalent temperature difference (NETD) with f/1.2 optics at 27°C background is 0.13°C at the HDTV output stage.

Heterojunction Ge_xSi_1-x/Si internal-photoemission infrared detectors are being developed for multispectral imaging in the middle-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) spectral bands. The detectors, which are fabricated by molecular beam epitaxy of degenerately doped Ge_xSi_1-x heteroepitaxial layers on Si, exhibit high responsivity uniformity, low dark-current noise, tunable cutoff wavelength out to 25 μm, and excellent producibility. High-quality MWIR and LWIR thermal imagery has been obtained for 320-x 244- and 400- x 400-element focal plane arrays consisting of Ge_xSi_1-x/Si detectors with cutoff wavelength of ~10 μm and monolithic CCD readout circuitry.

Several diffractive optical elements that operate in the infrared are presented. The microrelief structure is either a V-groove or binary lamellar and the features are of the size of one wavelength or below. The applications of these elements are beam deflectors, beamsplitters, beam attenuators, and polarizers.

An IR measurement technique that has been developed to measure electromagnetic (EM) fields is presented. This technique uses a minimally perturbing, thin, planar IR detection screen to produce a thermal map of the intensity of the EM energy over a two-dimensional region. Several examples of measured EM fields near radiating microwave sources and scattering bodies using IR thermograms are presented. These examples illustrate the use of this technique to correlate theoretical data with experimental observations and to experimentally validate complicated numerical codes that predict electric field distributions inside waveguide cavities (E fields) and surface current distributions on metallic surfaces (H fields).

Experimental evidence of periodic alternation of different transverse modes in a high-power CO₂ laser is interpreted in terms of local cooling of the discharge column, which corresponds to the maximum emitted intensity. Optogalvanic coupling between emitted intensity and local discharge impedance values yields a transverse redistribution of discharge current and, hence, of laser gain. Thus, besides the fast feedback provided by the cavity, with high-power lasers one must account also for a slow global feedback because of the optogalvanic effects.

The macroscopic spread function describes the extent to which radiation is spread in a semitransparent material because of surface and subsurface scattering. The objective here is to investigate the effects of optical and geometrical parameters on the macroscopic spread function of plastic reference samples and reagent strip formats. A new feature is the use of a fast raster area scattering instrument (FRASI) instrument in measuring the spread function data of the plastic samples and reagent strip formats. Experimental measurements show that least spreading is associated with the off-white plastic samples using a wavelength of 700 nm and a reflected angle of 55 deg. The results for the Glucofilm™ reagent strip formats indicate that most spreading occurred with the 45-deg reflected angle and that least spreading is associated with measuring these reagent strips at 800 nm. The spreading curve determined from the experimental data can greatly assist the reflectometer designer in selecting the optimum optical parameters and geometrical dimensions of the reference sample and the reflectometer system.

The breadth of activity in the field of infrared zoom lenses is international in scope. Representative infrared zoom lens systems of the 1990s from the continents of North America, Europe, and Asia and the Middle East are presented. Design considerations unique to the infrared spectrum such as athermalization are given special attention. The various approaches to solving these design problems are described along with the operating characteristics of these systems. Applications include forward-looking infrared scanning systems and target simulators. Tolerance considerations during manufacture are presented. Innovative reflective zoom systems are also considered. Development trends for the next several years are discussed, including the use of diffractive optical elements in infrared zoom lens systems.

The schiefspiegler is an optical system consisting of an arrangement of skewed mirrors forming, usually, an off-axis telescope. Considered here are such systems based on a pair of reflecting prolate spheroids that have a focus in common. Such a system possesses bilateral symmetry. A pseudoaxis is defined as a ray passing through each of the foci and being reflected off each mirror, which has the property that it is a line of symmetry for all other rays passing through these points. Conditions have been derived that ensure the existence of this pseudoaxis. The pupil planes of the system are located at each of the spheroids' foci. Additional conditions for image formation are derived. An example is given. The schiefspiegler is small compared to its rotationally symmetric counterpart and is capable of being folded into a small volume. This property makes it very suitable for satellite optics.

The European Space Research and Technology Centre (ESTEC) has developed a small, space qualified and TV compatible IR viewing system able to visualize thermal flows in fluids in microgravity. This instrument is a part of the diagnostics of a Spacelab facility, namely the Autonomous Fluid Physics Module (AFPM) flown on the last Spacelab D2 mission (April to May 1993). One of the main objectives of the research is to enable monitoring changes in the surface temperature of a fluid following the application of different stimuli. The only way to achieve this without disturbing the fluid under test is to use nonintrusive infrared measurement techniques. Starting from a basic commercial item, the Agema 870 scanner, ESTEC designed and built a thermal mapping diagnostic system provided with an autoranging capability that allows real-time temperature measurement in the range from 0 to 80°C and with a frame rate of 6 images/s. The geometrical resolution is 70 x 70 pixels in a field of view of 130 x 1 30 mm, which maps out the full temperature distribution of a typical fluid column experiment. An automatic compensation of the background noise at room temperature keeps the minimum resolvable temperature difference (MRTD) figure below 0.2°C. Therefore, the overall accuracy of the system allows one to follow the evolution of the complex phenomena related to the heat convection and mass transport effects at the surface of fluids in a weightlessness environment. The general design of the thermal mapping diagnostic (TMD) system is described and the technical solutions adopted to achieve the scientific goals of the investigation carried out with the AFPM are presented.

A six-feature all-sky star field identification algorithm has been developed. The minimum identifiable star pattern element consists of an oriented star triplet defined by three stars and their celestial coordinates and visual magnitudes. This algorithm has been integrated with a CCD-based imaging camera. The autonomous intelligent camera identifies in real time any star field without a priori knowledge. Observatory tests on star fields with this intelligent camera are described.

An analytical model for crosstalk is developed for an infrared scene projector that utilizes a deformable-mirror device as an infrared spatial light modulator. Partial-coherence effects that result from the physical layout of the projection system are included. Crosstalk is determined by defining a crosstalk ratio in the projected image. Crosstalk-ratio calculations are carried out for monochromatic and blackbody projection sources over the 3- to 5-μm wavelength band. The results predict crosstalk ratios of 260:1, 1200:1, and 2400:1 for deformable-mirror pixels of 50, 100, and 150 μm when a blackbody source is used in the projection system. Crosstalk performance is improved at shorter wavelengths and for larger deformable-mirror pixels. The results of a proof-of-principle experiment are included to verify the feasibility of a deformable-mirror device in the projection system.

Laser-induced retinal lesions are used to treat a variety of eye disorders such as diabetic retinopathy and retinal tears. Both the location and the size of the retinal lesions are critical for effective treatment and minimal complications. Currently, once an irradiation is begun, no attempt is made to alter the laser beam location on the retina. However, adjustments are desirable to correct for patient eye movements and tissue inhomogeneities. Lesions form in much less than 1 s and typical treatment for a disease such as diabetic retinopathy requires as many as 2000 lesions per eye. This type of tedious task is ideally suited for computer implementation. An instrumentation system has been developed to track a specific lesion coordinate on the retinal surface and provide corrective signals to maintain laser position on the coordinate. High-resolution retinal images are acquired via a CCD camera coupled to a fundus camera and video frame grabber. Optical filtering and histogram modification are used to enhance the retinal vessel network against the lighter retinal background. Six distinct retinal landmarks are tracked on the high contrast image obtained from the frame grabber using two-dimensional blood vessel templates. The frame grabber is hosted on a 486 PC. The PC performs correction signal calculations using an exhaustive search on selected image portions. An X and Y laser correction signal is derived from the landmark-tracking information and provided to a pair of galvonometer steered mirrors via a data acquisition and control subsystem. This subsystem also responds to patient inputs and the system monitoring lesion growth. To confine the laser position within a 1OO-μm-radius circle at a retinal velocity of 50 deg/s requires a position update 150 times per second. The development system is currently implemented on a 486 personal computer hosting a video frame grabber and data acquisition and control hardware. With a 33-MHz processor the current implementation provides 100-μm target radius at retinal velocities less than 2 deg/s. An overview of the robotic laser system design is followed by implementation and testing of a development system for proof of concept and, finally, specifications for a real-time system are provided.

A lossless image compression algorithm based on a prediction and classification scheme is presented. The algorithm decomposes an image into four subimages by subsampling pixels at even and odd (both row and column) locations. Because the four subimages have strong correlations to one another, one of them is used as a reference in predicting the other three, and the resulting differences between the predicted subimages and the original subimages are encoded. Even though these differences are decorrelated and tend to be random, there is still a relatively large correlation left between the estimated differences and the subimage used in prediction. For example, the estimated differences tend to be large in a high-detailed region, where pixel values change rapidly, whereas the differences are small in a low-detailed region, where pixel values change smoothly and slowly. This redundancy is exploited by dividing the estimated differences into subsets based on a slope change in the subimage used in prediction. The performance of the proposed algorithm using two different predictors, linear interpolation and third-order polynomial interpolation, is compared with that of the hierarchical interpolation (HINT) scheme and Fourier transform interpolation by measuring the first-order entropies of the estimated differences. With a third-order polynomial interpolation and division into two subsets, an average entropy of 3.1 bits/pixel is achieved for the three predicted difference subimages of the 12 bits/pixel x-ray computed tomography images. It is about 0.86 bits/pixel lower in the first-order entropy than the HINT for the three subimages.

Illumination wavelengths between 270 and 470 nm are evaluated to determine which wavelength produces the greatest difference between the fluorescence emission spectra of normal and atheromatous arterial tissues. Atherosclerotic plaques are considered as a diseased class and are further subdivided into three diseased subclasses-fibrous plaques, complicated plaques, and hard calcified plaques. The Mahalanobis distance squared, a statistical figure of merit describing class separability, is used to compare the illumination wavelengths. Classification accuracies are also estimated and used for comparison. Optimum classification performance is found to occur with illumination in the wavelength range 314 to 334 nm, except for hard calcified plaques, which are more accurately classified with illumination wavelengths longer than 380 nm. The issue of how much information is required from the fluorescence emission spectra to accurately classify tissue is also investigated.

We introduce subsampled convolution and convolution with an aggregate kernel as computationally efficient techniques for discrete convolution of the free-space propagation kernel with generalized and rectangular aperture functions, respectively, in computing near-field diffraction patterns. We develop fast Fourier transform based algorithms for implementing subsampled and aggregate kernel convolution, then demonstrate the memory and execution time economy of these techniques through computational examples.

Details are given on a novel type of display system based on traditional technology and capable of displaying truly three-dimensional computer-generated images that can be viewed concurrently from practically any orientation without the need for special glasses to be worn. The principle of operation is elucidated, data rate requirements are described, the prototype control system hardware is outlined, and pictures of some simple computer-generated shapes that have been displayed are included.

A microwave fiber optic link is developed for operation from 8 to 18 GHz. Modulation of a 1.3-μm wavelength optical carrier is accomplished using a lithium niobate Mach-Zehnder interferometer modulator that was designed for broadband operation up to 19 GHz. The link transmitter components, which consist of a high-power semiconductor laser, an optical isolator, and a modulator with polarization-preserving fiber pigtails, are spliced together to fit into a 10.16- x 5.08- x 2.54-cm3 (4- x 2- x 1-in.) box for applications where space is critical. The average link electrical gain is 45 dB, the frequency response is flat to within ±4 dB across the 10-GHz band, and the spur-free dynamic range of the link is 84 dB.

A simple method to determine the moduli of elasticity E and G and the Poisson coefficient v of a linear elastic isotropic structural material on the basis of a cylindrical beam, from a single double-exposure holographic interferogram, is described. The method is applicable to different types of materials. The measurement of a steel beam is presented as an example.

Double-exposure as well as real-time holographic interferometry are used to evaluate changes of the central curvature of the bovine cornea in vitro under small intraocular pressure differences. Double-exposure holographic interferograms of expanding corneas were used to get the positions of dark interference fringes on the surface of the cornea. Real-time holographic interferometry enables determining the absolute value of the displacement of the corneal center along the axis of the eye or the number of the fringe that is located closest to the corneal center. A mathematical model is given for the radial distensions and displacement of the center of curvature in two mutually perpendicular planes of a longitudinal section of the cornea along the axis of the eye. Examples of holographic interferograms of a bovine cornea recorded at an intraocular pressure of 1340 Pa and pressure differences of 10 and 20 Pa, respectively, as well as resulting changes of the corneal curvature are presented.

In-line holograms of iron oxide chain aggregate particles (diameter: 0.08 to 0.1 μm and length: 4 to 6 μm) were obtained using a divergent pulsed YAG laser and then optically reconstructed with a He-Ne laser. Although unable to resolve the actual particle dimensions, the reconstructed images are adaptable to image processing techniques. The fiber orientation distribution can be determined from these techniques.

An improved technique for rotating prism (or wedge) multiplex holography is proposed. A practical application of this technique to holographic interterometry is also presented. Theoretical analyses and experimental results are provided for the center track of the multiple images during the reconstruction and the calculation of their number and their separation. The results of the experiment coincide with the theory.

Holographic diffusers are prepared using silver halide (Agfa 8E75 and Kodak 649F) and photopolymer (Polaroid DMP 128 and DuPont 600, 705, and 150 series) media. It is possible to control the diffusion angle in three ways: by selection of the properties of the source diffuser, by control of its subtended angle, and by selection of the holographic medium. Several conventional diffusers based on refraction or scattering of light are examined for comparison

A common problem in manufacturing design is the accurate rendering of a 3-D object into a digitized 3-D representation. Such a rendering can be used to duplicate or modify existing objects as well as perform quality control and object recognition in automated manufacturing operations. A structured light technique that uses a sinusoidal illumination pattern to retrieve 3-D information is presented. This technique requires only one image of a surface area to process the topology and can be accomplished with incoherent light. The sine section technique projects a sinusoidal pattern onto an object and recovers the local slopes (first order), which are then combined to reconstruct the surface topology. Surface variations act to create a wideband frequency modulation (zero to infinite frequency), so an optimum frequency demodulation technique is developed to yield average slopes in local regions of the illuminated area. A reconstruction algorithm is introduced that uses these slopes with minimum mean square error. The performance of this technique appears to be very robust and insensitive to intensity variations. Results are presented for recovery of synthesized surfaces corrupted in altitude by additive colored Gaussian spatial noise. The colored noise is generated with a fractal filter to best emulate real surface topologies.

The effective blackbody temperature used to specify the radiant output from an IR projector is defined formally as the temperature assumed by the blackbody target that generates the same signal radiance as the IR projector characterized. Analytical expressions and graphical analyses are developed enabling the calculation of the blackbody temperature in terms of both the actual device temperature and a specified active zone attenuation coefficient, the latter quantifying the deviation from blackbody behavior. Both the projector signal radiance and the signal current developed in the imaging unit under test illuminated by the projector are shown to be readily calculable once the value of the effective blackbody temperature is known. The analysis is applied to the comparison of the thin film resistor, silicon bridge resistor, and suspended membrane resistor emissive IR projection technologies.

The optical considerations that need to be addressed during the design of IR projectors intended for application within real-time hardware-in-the-loop simulation systems are examined. Attention is paid to the form of the spatial frequency transfer function and, thereby, to the factors that affect the spatial resolution within the composite optical system defined by the IR projector and the imaging unit under test, with particular emphasis on the sampling effects (aliasing) that need to be avoided.

A modification of the conventional Michelson interference spectrometer is proposed that replaces the extremely precise translational motion with a single uniform velocity rotation of one perpendicular double mirror. The formulas of the optical path difference and the light displacement are deduced. The calculated data show that the path difference has good linearity with the rotation angle. The characteristics of this design are also analyzed.

A theoretical analysis of the fringe location error of a sampled intensity distribution when using a zero-crossing algorithm is performed. The theory assumes a sinusoidal distribution with local constant phase modulation. The error function is analyzed with respect to the number of pixels per fringe period α, the location of the fringe maximum within a pixel, and the error in computing the mean intensity. It is shown that for reasonable values of α, the fringe location error will be less than the error caused by jitter in the line sync signal if the error in the mean intensity is kept below certain limits.

The clustering problem refers to the partitioning of target sightings into sets. Two sightings are in the same set if and only if they are generated by sensor detections of the same target and are in the same great circle arc (GARC) trajectory of that target. A Boltzmann machine is developed whose sparse architecture provides for only partial constraint satisfaction of the associated cost function. This together with a special graphics interface serve as an aid in determining GARCs. Our approach differs from others in that the neural net is built to operate in conjunction with a non-neural tracker. This further restricts the architectural complexity of the network and facilitates future experimentation regarding decomposition of the neural net across several Von Neumann processors. Also, the Boltzmann machine architecture eases the effort of finding optimal or near optimal solutions. Results are presented. The demonstrated feasibility of neural GARC determination encourages investigation into the extension of its role in the track formation process utilizing an environment that includes supercomputers, neurocomputers, or optical hardware. The network architecture is capable of identifying a host of geometric forms other than GARCs and can thus be used in several domains including space, land, and ocean.

Luminaire designs based on multiple asymmetric nonimaging compound parabolic reflectors are proposed for 2-D illumination applications that require highly uniform far-field illuminance, while ensuring maximal lighting efficiency and sharp angular cutoffs. The new designs derive from recent advances in nonimaging secondary concentrators for line-focus solar collectors. The light source is not treated as a single entity, but rather is divided into two or more separate adjoining sources. An asymmetric compound parabolic luminaire is then designed around each half-source. Attaining sharp cutoffs requires relatively large reflectors. However, severe truncation of the reflectors renders these devices as compact as many conventional luminaires, at the penalty of a small fraction of the radiation being emitted outside the nominal cutoff. The configurations that maximize the uniformity of far-field illuminance offer significant improvements in flux homogeneity relative to alternative designs to date.

An optical multiprocessor that can perform binary full addition and full subtraction in parallel is designed using a joint transform correlator. A new coding scheme is also developed for the proposed technique. Finally, simulation results are presented to verify the effectiveness of this scheme.

The potential for substantial threshold reduction in stimulated Brillouin scatter phase conjugate mirrors (PCMs) was systematically studied using tapered hollow glass waveguides filled with carbon disulfide. Using a low-threshold PCM of 100 cm straight section length and 10 μm inner diameter, the threshold was reduced by a factor of 1000 compared to the bulk liquid threshold. Use of a tapered input alleviated alignment sensitivity normally encountered with small-input-diameter fibers, and allowed for the fabrication of wide-field-of-view PCMs (and Brillouin amplifiers) of a type useful in many applications. Performance of the low-threshold PCM was found to meet theoretical expectations.

Inhomogeneous dielectric surfaces exhibit both diffuse and specular reflection components. Although various reflection models have been proposed for both of these components, the prediction of the relative strengths of these components in computer vision and computer graphics has so far not had a strong physical motivation. We propose a reflectance model for combined diffuse and specular reflection from dielectric materials that involves purely physical parameters (i.e., no ad hoc weighting of specular and diffuse components). This reflectance model is used to predict the relative strength of diffuse and specular reflection components ih terms of imaging geometry, dielectric surface parameters, and solid angular extent of incident light. We derive lower bounds on the contrast ratio between a specularity and surrounding diffuse reflecting regions. These can be used effectively to rule out highly contrasting diffuse reflecting regions being misidentified as pecularities under a number of conditions that can significantly aid intensity-based specularity detection methods, and in turn image understanding. The presented theoretical developments can be used to predict the photometric dynamic range of illuminated objects, which can be essential to inspection methods in machine vision. These developments can also be used in computer graphics for the physically precise rendering of the relative strengths of specular and diffuse reflection from inhomogeneous dielectrics.

Current Air Force interests include a desire to track an object based on its shape once it has been designated as a target. The use of a correlation-based system to track an object through a series of images based on templates derived from previous image frames is discussed. The ability to track is extended to sequences that include multiple objects of interest within the field of view. This is accomplished by comparing the height and shape of the template autocorrelation to the peaks in the correlation of the template with the next scene. The result is to identify the region in the next scene that best matches the designated target. In addition to correlation plane postprocessing, an adaptive window is used to determine the template size to reduce the effects of correlator walkoff. The image sequences used were taken from a forward-looking infrared sensor mounted on board a DC-3 aircraft. The images contain a T-55 tank and both an M-113 and a TAB-71 armored personnel carrier moving in a columnized formation along a dirt road. This research presents techniques to (1) track targets in the presence of other, and sometimes brighter, targets of similar shape, (2) to maintain small tracking errors, and (3) to reduce the effects of correlator walk-off.

A submicrometer-diameter x-ray beam from a tapered glass capillary is used to image micrometer-wide metal stripes on a lithography sample consisting of a 1000-Å-thick gold pattern on a silicon wafer substrate. An image of the gold pattern with submicrometer resolution is easily observed by measuring the transmission of x-rays through the sample as it is scanned in two dimensions. The size of the x-ray beam leaving the tip of the capillary was determined to be 0.10±0.01 μm by fitting a function to data obtained from transmission and fluorescence measurements as the edge of a gold stripe was scanned across the end of the capillary. Using the same capillary, Laue diffraction was observed from a 500-μm-thick silicon wafer in a 10-s exposure corresponding to an illuminated volume of 3.9 μm³. The x-ray intensity (flux/area) of the beam leaving the pipette was shown to be 960 times higher than the intensity entering the pipette, at 6 keV. As the ability to fabricate tapered capillaries improves, many new experiments with submicrometer x-ray beams including Laue diffraction from significantly smaller volumes should be possible.

This PDF file contains the letter “Letter: Invariant analog wavelets [see 33(1)307-308(Jan1994)]” for OE Vol. 33 Issue 01

This PDF file contains the letter “Letter: Comment on Special Section on Wavelet Transforms: Optical Versus Digital Implementation of the Wavelet Transform” for OE Vol. 33 Issue 01

This PDF file contains the editorial “Book Rvw: Speckle Metrology," edited by Rajpal S. Sirohi for OE Vol. 33 Issue 01