This PDF file contains the editorial “Editorial: 1994 in Review: Part I” for OE Vol. 34 Issue 02

This PDF file contains the editorial “Guest Editorial: High Heat Flux Optical Engineering” for OE Vol. 34 Issue 02

As power levels of synchrotron beamlines increase, the heat flux on optical components attains or exceeds levels of that for high-energy laser (HEL) optics. The synchrotron technical community may benefit from the experiences gained as a result of the development activities associated with cooled mirrors for HELs. Such activities span a period of about 25 years, consider numerous design concepts, and evaluate many construction materials along with related fabrication processes. The quantity of work performed on cooled mirrors for HELs is too extensive to allow a single paper to summarize all potentially useful information. The purpose of this overview is to highlight much of the past work, with emphasis on more recent technology, and to provide a bibliography that should aid in accessing pertinent literature. Although heat loads are similar, hundreds of watts per square centimeter, some aspects of the laser and synchrotron application differ. Generic characteristics of each are summarized before prior cooled laser mirror technology is discussed. This should allow a meaningful assessment of the applicability of prior heat exchanger designs, material selections, and operational experiences to synchrotron beamline usage.

Mirror jitter is a flow-induced vibration phenomenon typical of convectively cooled optics. Flow separation points within the coolant supply lines, mirror manifolding, and mirror coolant passages produce internal turbulent pressure distributions, which lead to unbalanced fluctuating forces and resultant mirror jitter. The author reviews the known causes of jitter, methods to determine jitter forces as well as actual mirror jitter, and methods to measure jitter forces. A summary of known jitter force measurements is given, and an extensive bibliography of relevant literature is listed. Guidelines for evaluating system jitter and avoiding pitfalls are offered.

The thermal distortion test facility (TDTF) at Phillips Laboratory provides precise measurements of the distortion of mirrors that occurs when their surfaces are heated. The TDTF has been used for several years to evaluate mirrors being developed for high-power lasers. The facility has recently undergone some significant upgrades to improve the accuracy with which mirrors can be heated and the resulting distortion measured. The facility and its associated instrumentation are discussed.

Technologies based on porous media can be used in several classes of heat exchangers that can be used to meet the cooling needs of high heat load optical components as well as other high heat flux applications. These include mechanically pumped single-phase and two-phase porous media heat exchangers, as well as capillary pumped (heat pipe) two-phase designs. A brief overview of each of these classes of heat exchangers is given, and several applications representative of the state of the art are described. Various specific technologies are discussed that have demonstrated the capability to dissipate heat fluxes greater than 1000 W/cm² over areas of interest in optics applications. Finally, an assessment is given of the capabilities of each approach to meet the needs of specific applications.

The optical and the power characteristics of various synchrotron radiation sources are summarized. The optical characteristics-flux, brightness, coherence, polarization, etc-determine the quality of the source for photon experiments. The power characteristics determine the heat load on beam-line elements. After discussing the cases of the bending magnet, wiggler, and undulator, the case of the helical undulator is considered separately, emphasizing its different power characteristics from the planar case.

We discuss the specification of x-ray mirror surfaces in terms of their imaging perlormance and express the results in terms of quantities that are directly accessible from laboratory profile measurements. Procedures are illustrated by strawman examples in glancing- and normal-incidence geometries.

The substantial increase of brilliance produced by new dedicated synchrotron sources calls for equivalent progress in the performance of beam-line instrumentation. One of the basic aims is to obtain more precise focusing while collecting more photons. In particular, considering both the multiple functions of x-ray mirrors as beam-line components and the various characteristics of insertion devices as x-ray sources, a best compromise must be found among three concurrent requirements: versatility, high quality, and stability under severe working conditions. The author presents an overview of optical, thermal, and mechanical problems encountered with the design and realization of x-ray mirrors for third-generation synchrotron sources. The case of the European Synchrotron Radiation Facility is discussed to illustrate the specific requirements when dealing with the new hard x-ray insertion devices.

Developments of vacuum ultraviolet (VUV) mirrors and optical elements for intense synchrotron radiation in Japan are reported. High heat load tests of chemical-vapor-deposited silicon carbide (CVD SiC) mirrors, 500 x 50 x 40 mm³, were successfully made for undulator radiation with heat flux of 0.4 W/mm². As extensions of various CVD SiC mirrors developed at the Photon Factory, the largest CVD SiC mirror with sintered SiC substrate, 1000 x 140 x 25 mm³, and the thin CVD SiC mirror, 300 x 50 x 5 mm³, were fabricated by the SP-ring 8 project. Heat load tests of a CVD-SiC-based grating and a multilayer mirror exhibit possibilities of making high heat load optical elements in the VUV and soft x-ray (SX) regions. Measurements of optical properties of CVD SiC mirrors produced by different methods showed that the optical constants in the VUV and SX regions were almost equal to one another. A profilometer for measuring surface figures of large-size aspheric mirrors was constructed on the basis of the Twyman-Green interferometer with heterodyne phase detection method.

The new properties of third-generation synchrotron radiation beams call for corresponding progress in instrumentation technology. This is particularly true for hard x-ray mirrors, for which new technologies have been implemented to meet outstanding requirements. The transfer of experience from other fields such as high-energy lasers and astronomy has been of major importance in the realization of new designs. The European Synchrotron Radiation Facility, the first third-generation hard x-ray source in Europe, has stimulated R&D programs of four European companies in the field of hard x-ray mirrors. This paper presents the major achievements of these companies.

High heat loads on optical components in next-generation synchrotron radiation sources will require the use of sophisticated methods to prevent surface distortion that would degrade the intrinsic source brightness. In some cases it is desirable to be able to measure the mirror figure under actual operating conditions in ultrahigh vacuum. We propose to modify the standard long-trace profiler configuration to enable scanning profiler measurement of mirrors under actual high heat load conditions. The modification entails the use of a penta prism on a translation stage inside the vacuum chamber, with the optical head mounted outside the chamber. This configuration is similar to the original pencil-beam interferometer system developed by von Bieren, but it contains a number of modifications that enhance its accuracy.

The need for high heat load optics has its origin in high-energy laser systems designed in the 1970s and 1980s. The advancement of these systems to shorter wavelengths and higher flux levels and the inclusion of aspheric surfaces provided the early impetus for developing optics with advanced internal heat exchanger designs and for improved processes for polishing and testing associated optical surfaces. Today this technology continues to evolve for use in third-generation synchrotron beamlines, an emerging scientific application offering far-reaching implications for materials research , pharmaceutical development, micro-machining, and integrated circuits. Components for these applications require grazing incidence optical prescriptions and special polishing techniques, often leading to the construction of new equipment and the development of suitable polishing processes and optical test procedures. An overview is provided of the advancing state of polishing and testing techniques supporting a developing class of high heat load optical components characterized by rigorous slope error tolerances and demanding surface roughness specifications.

The design principles and special advantages of monolithic adjustable-radius metal mirrors are now well established. Such mirror systems are usually cut from a single block of metal by a wire-electric-discharge machining system, and they consist of a bendable mirror joined to its bending device by thin webs of metal that can be treated as hinges. Analysis is provided for understanding the response of such mirrors to the unintended couples they receive from these flexural hinges when the hinge angle is not zero. The rigidity (the couple per unit angle) of the usual types of flexural hinge and of the most common mirror shapes are calculated thus allowing the hinge-induced distortions of any mirror surface to be estimated. The analysis includes mirrors both with and without water-cooling channels. Two strategies for reducing the errors are proposed. One involves the design of sufficiently flexible hinges and the other the elimination of the hinge rotations (and therefore their couples) altogether by means of a new design principle. Some analysis of the latter scheme is provided including a prescription for choosing suitable design parameters.

The Advanced Photon Source (APS) has embarked on a systematic program in high heat load x-ray monochromator optics to mitigate the thermal effects due to the powerful x-ray beams at third-generation synchrotron sources. This program includes both experimental and computational studies. The approaches being studied include the use of new coolants (cryogens and liquid gallium), new crystal geometries (inclined and variable asymmetric), and new materials (diamond). The paper summarizes the high heat load monochromator program at the APS.

Cryogenic cooling of x-ray optics is now a well-proven technology when used to reduce thermal distortion. A review of the work done on this subject includes the following aspects: fluid technology, cooling geometries, limits of cryogenic cooling, and integration inside a monoch romator.

A review of the performance of diamond single crystals as a high heat load optical component for synchrotron x rays is given. It has been proven experimentally that the bandpass and the angular divergence of the monochromatic beam provided by a relatively thin diamond crystal used in an undulator beam are not degraded by thermal effects for a total power up to 280 W (8.7 W absorbed) at a heat flux up to 3.5 kW/mm² (109 W/mm² absorbed). These high heat load tests and model calculations have shown that edge-cooled diamond crystals at room temperature provide an easy and widely satisfactory solution to the heat load problems generated by undulator beams that are currently foreseen at the third-generation storage rings of the European Synchrotron Radiation Facility, the Advanced Photon Source, and the SPring-8 facilities. For this cooling geometry, diamond single crystals offer the additional advantage that beam multiplexing can be used. Currently available synthetic diamond crystals are sufficiently big for undulator beams and their crystalline perfection is adequate. Most of the crystals actually in use were prepared with their big surfaces (about 30 mm² in size) oriented parallel to the (100) netplanes, but more recently bigger samples whose surfaces are parallel to the (111) lattice planes were obtained. Thus, diamond single crystals are superior to all other monochromator materials for undulators and for cases where a loss of a factor of 2 in flux combined with a similar gain in resolution (as compared to silicon) are compatible with the experiments.

Using special channel geometries, the efficiency of water cooling of silicon crystals at room temperature can be improved to the point where it becomes very attractive for use with x-ray monochromators at high-power synchrotron radiation beamlines. Prototype monochromators using two different geometries have been built and tested. The microchannel geometry uses long, parallel channels approximately 50 μm in width. The pin-post geometry creates a two-dimensional network of submillimeter water passages. Both geometries have excellent thermal performance, though preparing strain-free crystal assemblies containing such small features remains problematic. When perfected, water cooling using microchannel or pin-post geometries should be particularly suited to monochromator crystals used at wiggler beamlines.

Multilayers are the optical elements of choice in any situation where flux rather than resolution is desired. They can be tailored to optimize either reflectivity at fixed or variable energy, or heat resistance, or bandpass, or harmonic rejection. The present state of the art of x-ray multilayers is presented, and the possible applications are reviewed, including the use of multilayers as soft x-ray polarizers, large-passband elements for hard x-rays, and power filters. In the situation of very intense beams the increase of temperature can produce significant changes of reflectivity, which have been extensively studied at the microstructure level in some cases, such as W/C, W/Si, and Mo/Si. Existing and prospective solutions are detailed, including heat treatment prior to x-ray exposure, use of compound materials, efficient cooling, and modification of the electric field distribution by nonperiodic arrangements.

Bonded silicon-on-insulator (SOI) structures with oxide-nitrideoxide (ONO) layers are investigated nondestructively using spectroscopic ellipsometry (SE). Results are discussed from three main points of view: the effects of the beam size on evaluating the S0I substrate, the beam divergence, and the effect of applying different data-fitting parameters to get reliable structures. Optimum results for a wavelength range of 250 to 850 nm have been obtained by using a combination of a lens and a slit of nearly 1-mm width to minimize the light-beam divergence. One interesting result is that because of the observed slight vertical error, and because the measured parameter tanψ has values greater than one, we have to avoid in this case fitting tanψ and cosΔ in order to obtain calculated data close to the nominal values. No depolarization effects were found for the obtained ellipsometric data.

A two-fiber laser Doppler anemometer was built and tested with the fiber probe placed parallel to the flow. Nine combinations of fiber diameters and fiber separations were tested, and the dominant and maximum shift frequencies were plotted as a function of the unperturbed (or freestream) flow velocity. For both the forward (toward the fiber tip) and reverse (away from the fiber tip) flow directions, the graph of the flow velocity against the maximum shift frequency shows better linearity and approaches closer to the theoretical line than the graph of the flow yelocity against the dominant shift frequency. For the forward flow, the Doppler frequency is close to that predicted and linear above 20 cm/s, but for the reverse flow the slope is only one-quarter of that predicted. Analysis of the data showed that the region of flow perturbation decreases towards the fiber tips in the forward flow, whereas it extends away from the fiber tips in the reverse flow. In its present form, the two-fiber system cannot then be used for accurate blood velocity measurements, since linear calibration between the forward and reverse flow velocities cannot be achieved.

A two-bandpass prototype radiometer utilizing a silver halide optical fiber for temperature measurements is constructed. Preliminary results show the feasibility of the two-bandpass method for ambient temperature measurements. Using this method, errors arising from geometrical factors and emissivity changes can be eliminated or reduced.

We describe a practical method for monitoring the evolution of the depth of grating structures exposed in photoresist during development of the resist. A diagnostic laser of nonexposing wavelength illuminates, through a quartz window, the grating surface immersed in developer solution. The intensity of the diffracted - 1 order is monitored. The intensities vary with time due to feature growth by dissolution. Using realistic models for the shape of the grooves created, we predict grating efficiency versus feature geometry for the grating in both air and developer solution. This knowledge allows us to make a determination of the stopping point during development that gives us the maximum grating efficiency for operation in air. The shape of the efficiency curve versus time during development also makes possible the determination of complete dissolution of the grating troughs to the substrate. This real-time monitoring corrects for exposure and bake variations, for example, and it permits the recycling of developer solution and thus decreases the waste stream for grating manufacture. It also allows for the determination of the end point for deep (>500 nm) gratings that show multiple extrema during development.

The photosensitive organic system of poly(vinyl carbazole) doped with spiropyran is studied for real-time reversible holography. The photoinduced reversible color change between thermally stable and metastable states of spiropyran molecules can modulate the absorption and the refractive index of the spiropyran-doped polymer film. Erasable holograms can be recorded in either stable or metastable states of such films of thickness 10 and 50 μm prepared by a gravity settling method. The grating constant achieved was δ= 0.58 μm, using the 350-nm UV line of a krypton-ion laser. It has been found that write-read-erase cycles can be performed repeatedly. High-efficiency erasable holographic recording at 350 nm has been performed in these films, and a diffraction efficiency greater than 10% has been achieved.

A comparative time-averaged TV holographic technique that allows fringe compensation is presented. The technique employs two identical objects, the test and the master, that are subjected to sinusoidal vibration to detect the difference in either out-of-plane vibration amplitude or phase distributions. In addition, the present optical configuration offers simultaneous visualization of vibration amplitudes of the test object. Detailed theoretical and experimental results are presented.

In a two-beam, white-light, or polychromatic-Iight interferometer, any path-length difference in the beamsplitter introduces wavelength- dependent path delay because of the glass dispersion. A technique to align balanced path is described. The method is based on two- or three-wavelength simultaneous interferometry. Difference in intensity of fringes placed symmetrically around the zero interference order (ZIO) is used to measure and equalize the beamsplitter path (BP). As a polychromatic source of light. 660-, 840-, and 780-nm wavelength mixed beams of multimode laser diodes are applied. The technique allows us to balance the path difference with an accuracy better than ± 0.2 μm. Theoretical background and experimental verification of the method is presented.

An incoherent (direct detection) Doppler lidar is developed that operates in the middle of the visible spectrum and measures wind and aerosol profiles during the day and night from the planetary boundary layer to the lower stratosphere. The primary challenge of making a lidar measurement in the visible spectrum during daylight hours is the strong presence of background light from the sun. To make a measurement of this type, the laser line must be isolated spectrally to the greatest extent possible. This has been accomplished through the use of a multiple étalon Fabry-Pérot interferometer in combination with a narrow-band filter. The incoherent technique and system are a modified version of the Fabry-Pérot interlerometer and image-plane detector technology developed for an earlier Doppler lidar developed at the University of Michigan and for the High-Resolution Doppler Imager (HRDI) now flying on the Upper Atmosphere Research Satellite. The incoherent Doppler analysis is discussed and sample measurements are shown. Winds are measured in the boundary layer with 100-m vertical resolution and 5-mm temporal resolution with 1 to 3 m s^-1 accuracy.

As part of a communication channel, clouds cause spatial widening and attenuation of optical pulse power. Free-space optical communication from satellite to earth (ground or airplane) occasionally involves clouds over part of the optical channel. Most of the energy of optical pulses propagating through thin clouds passes through the clouds. The propagating energy is concentrated around the center of the beam. The distribution of the energy relative to the center of the beam is not uniform. Using the received energy in an efficient way reduces the transmitter power needed for given bit error rate. The advantages of low transmitter power are less radiation exposure and greater immunity to eavesdropping. To use the received energy efficiently, a mathematical model of spatial widening of the optical beam is derived using Monte Carlo simulation. The simulation is carried out at three different wavelengths in the visible and the near IR. Important aspects of this work include the fact that (1) using shorter wavelengths such as 0.532 μm results in least spatial widening and maximal received power, and is thus preferable for optical communication, and (2) the mathematical model derived is a basis for adaptive communication with less transmitted energy consumption.

Optical communication must contain clouds as parts of communication channels. Propagation of optical pulses through clouds causes widening in the spatial domain and attenuation of the pulse radiant power. These effects decrease the received signal and increase bit error rate (BER). One way to improve the BER of the communication system is by using adaptive methods to obtain more signal relative to noise power. Based on mathematical models of spatial widening of optical radiation derived by Monte Carlo simulation, a mathematical model for optimum performance of digital optical communication through clouds is developed. The purpose of the optimum adaptive communication system suggested here is to improve the BER by optimizing according to meterological conditions the spatial distribution of the detected radiation beam using a detector array where the external amplification of each detector is adaptable. Comparison and analysis of three models of communication systems in fog cloud channels are presented: (1) the optimum adaptive detector array aperture, (2) an ordinary single detector aperture of the same size, and (3) a small detector aperture. Improvement of more than four orders of magnitude in BER under certain conditions is possible with the new adaptive system model.

We describe the optical design of an optoelectronic 3-D system that is being developed by the Optoelectronic Computing Systems Center at the University of Colorado to prove the utility and viability of 3-D computers that use free-space optical interconnects to achieve a high degree of global connectivity among the PEs of a fine-grained parallel computer. The features of the VCSEL array as a source of coherent emission for hologram reconstruction and the CGH design procedure are discussed. An optical design in paraxial approximation of the 3-D computer with bidirectional 8 x 8 holographic interconnects is presented. The effect of VCSEL wavelength variation on diftraction crosstalk is estimated. The aberration in optical system based on the shelf objective is calculated, and a distortion compensation procedure is proposed.

We present a real-time optical processor intended for analyzing missing dots in a diffusely reflective screen dot pattern printed on paper. The coherent input image is generated with a liquid crystal incoherent-to-coherent image transducer. A rigorous theoretical calculation of the intensity distribution in the optical Fourier plane is made for a screen dot pattern with and without missing dots. Experimental resolution measurements of the system are shown, the optical Fourier transform of the diffusely reflective screen dot pattern is demonstrated, and the relation between intensity in the Fourier plane and percentage of missing dots is experimentally verified.

Detection of particles deposited on both smooth and patterned silicon surfaces is examined in terms of maximizing the signal-to-background ratio. Components of the signal and background are examined separately. To understand the origin of the collected signal, laser light scattering of individual polystyrene spheres deposited on a polished silicon surface is studied. It is shown that for sphere sizes of 1 to 20 μm, scattering is an interference phenomenon of light from two sources: one is the reflection of the laser light on the particle, the second is the reflection on the silicon surface after two refractions. The effect of illumination under different angles is estimated and compared with experiment on spheres as small as 100 nm in diameter. The background scatter produced by patterned wafers is also examined. Techniques for its reduction, such as optimization of the azimuthal illumination angle, and in the case of high-density dynamic random access memory (DRAM) wafers, by Fourier filtering, are presented. In regard to the latter, the effects of a selective filtering of this diffraction pattern are examined vis-à-vis the resultant perturbation of the relatively weak transforms of the actual particulates. It was found that even some of the most rudimentary of spatial filters can be used to achieve noteworthy improvements in detection sensitivity. Achievements are reported of up to 5x improvement in SNR for intradie measurements and up to 10-fold improvement in total particle count.

A simple technique for in-line alignment of features that are axially separated is discussed. The precision of the technique is 2.5 μm or better.

Thin and highly flexible telescope mirrors need to be supported carefully to avoid undesirable elastic deformations and a reduction of their optical quality. In this study, a wide variety of support topologies are examined to provide a basic set of optimized point supports for these telescope mirrors. This is carried out for mirrors without a central hole, with circular and annular entrance pupils. Efficient topologies introducing a small amount of zenith-angle-dependent defocusing are also proposed. The number of supporting points ranges between 3 and 36. Optimal forces and locations of point supports are calculated using thin-plate bending theory. Numerical methods include a linear least-squares method for determining the best forces, and a downhill simplex algorithm to optimize the support locations. The robustness of the proposed solutions is tested by simulated annealing. Scaling laws are briefly reviewed, and support efficiencies are given for each optimized topology. Results show that taking into account the central obscuration ratio (annular pupil) and tolerating a homologous (paraboloidal) deformation of the mirror allows an improvement of efficiency of up to 50% over the case of an unobscured pupil where defocus is not permitted. This work includes a study of support efficiencies versus the Poisson's ratio of the mirror material. Wavefront errors are also estimated in the case of a defective cell, to specify tolerances on forces and support locations.

Space optical systems generally require near-theoretical performance in hostile environments within size, weight, and cost constraints. We have addressed the challenge of achieving an optimum image quality through a cost-effective tolerance analysis scheme. Two different space optical systems are considered: the UV imager for the International Solar Terrestrial Physics (ISTP) Mission and an afocal telescope for the Advanced Polarized IR Imaging Sensor (APIRIS). These systems are described along with their required performances and designs. A tolerance study is conducted, and the effect of tolerances on image quality and cost is presented.

The dispersion characteristics of a diffractive micro-Fresnel lens (MFL) which is mass-produced for a laser diode collimator are examined for novel applications. The MFL's resolving power (Rayleigh criterion for resolution) at the design wavelength is calculated to be comparable to that of conventional dispersing prisms of the same size. A simple spectrometer with an MFL (4.5 mm diameter, 14.83 mm focal length at 0.78 μm design wavelength) and a movable pinhole (PH), is fabricated. The optimum PH diameter for both resolving power and light efficiency is 5 m, and the resolution and efficiency at the design wavelength are estimated to be 3.7 nm and 85%, respectively. The measurable spectral range determined from both the diffraction efficiency and the free spectral range of the MFL almost covers the entire visible region. The absorption spectrum of KMnO₄ solution is roughly obtained using the spectrometer. The space between the MFL and the PH, and the PH's movable length, which are required for spectroscopy, are as short as 20 and 7 mm, respectively. The simple and straight-line-structured spectroscopic system utilizing a more cost-efficient MFL may lead to the realization of less expensive and compact spectrometers.

A novel spectrophotometer based on the deflection of a secondary element for measuring clear and highly turbid materials within the millisecond time range is developed. The number of optical components of the monochromator is reduced to the absolute minimum. This results in excellent light throughput and a low stray-light level. The spectrophotometer has been designed allowing spectral measurements of absorption, transmission, reflection, and luminescence in a single-beam mode, as documented by various examples. Its design is highly flexible and the price/quality relation might be adopted to the envisaged purpose. The main philosophy is to relocate as many functions as possible from the hardware to the software part of the spectrophotometer. Several novel procedures based on old concepts are proposed. An appropriate computer program providing data acquisition, control functions as well as numerous analytical capabilities is developed on the basis of the compiler language power basic and indispensibly "fast" routines are written in assembler language.

Ion-beam sputter deposition (IBS) and dual-ion-beam sputter deposition (DIBS) of tantalum oxide films was investigated at room temperature and compared with similar films prepared by e-gun deposition. The optical properties, i.e., refractive index and extinction coefficient, of IBS films were determined in the 250- to 1100-nm range by transmission spectrophotometry and at λ = 632.8 nm by ellipsometry. They were found to be mainly sensitive to the partial pressure of oxygen used as a reactive gas in the deposition process. The maximum value of the refractive index of IBS deposited tantalum oxide films was n = 2.15 at = 550 nm and the extinction coefficient of order k = 2 x 10^-4. Films deposited by e-gun deposition had refractive index n = 2.06 at λ = 550 nm. Films deposited using DIBS, i.e., deposition assisted by low energy Ar and O₂ ions (E_a = 0 to 300 eV) and low current density (J_i = 0 to 40 μA/cm²), showed no improvement in the optical properties of the films. Preferential sputtering occurred at E_a(Ar) = 300 eV and J_i = 20 μA/cm² and slightly oxygen deficient films were formed. Different bonding states in the tantalum-oxide films were determined by x-ray spectroscopy, whereas composition of the film and contaminants were determined by Rutherford backscattering spectroscopy (RBS). Tantalumoxide films formed by IBS contained relatively high Ar content (≈ 2.5%) originating from the reflected argon neutrals from the sputtering target whereas assisted deposition slightly increased the Ar content. Stress in the lBS-deposited films was measured by the bending technique. IBS-deposited films showed compressive stress with a typical value of s = 3.2 x 10⁹ dyn/cm². Films deposited by concurrent ion bombardment showed an increase in the stress as a function of applied current density. The maximum was s ≈ 5.6 x 10⁹ dyn/cm² for E_a = 300 eV and J_i = 35 μA/cm². All deposited films were amorphous as measured by the x-ray diffraction (XRD) method.

A novel tracking system is developed and a prototype constructed. The tracker uses three gradient index lenses as a multiaperture vision system (MAVS). The three gradient index lens tracker (3GILT) uses the overlapping field-of-view region of the three lenses for tracking a point source. Thus, no moving parts are required. A single detector is used with each gradient index lens. The three detector signals are analyzed to determine the location of the point source or target. The experimental results agree with the theoretical analysis, indicating that the major performance parameters are identified and understood.

The effect of external energy source on waveguide's transmitted blackbody radiation is examined. It is shown that the radiometric signal is increased because of external heat sources. This effect can be avoided by a proper external protecting layer. The transmitted laser energy is another cause of heating the waveguide's walls. To analyze these effects, the wall temperature was recorded by thermocouples and thermal camera. It is shown that the most-affected regions in the waveguide are the curved regions and the distal end. Gas cooling and external metal layers reduce this undesired heating of the walls.

Abstract not available.

This PDF contains the communication on "Implementation of a bipolar neural network using a single optical channel."

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