Quantitative digital microscopy and analysis of fluorescence gels are examples of applications where images are acquired, usually with a video camera and frame grabber, for further processing and analysis. The use of a standard video camera and frame grabber creates problems in the subsequent data analysis, due to the nonlinear relation between the camera output and the optical input, and due to pixel jitter. In addition, the data are degraded by conversion to a standard video format followed by sampling at a rate determined by the frame grabber's image memory. In this work, an image processing workstation is described which uses a low cost ($850) 8-bit digital CCD camera in place of the video camera/frame grabber combination. The system has excellent linearity and high dynamic range. Proper setup and calibration of this system is essential, and procedures which were developed for this purpose are described. The results which were obtained are compared to those of a standard video camera. The tradeoffs involved in the use of this low cost system are discussed, and examples of data obtained with the system are presented. Although this system cannot replace a 12-bit or 16-bit digital camera in all applications, it can do so in many applications, at a price that makes widespread use of image quantitation systems practical.

Optical Fourier analysis has been used to estimate quantitatively the bone tissue structure. The two dimensional power spectrum of the light transmitted through the trabecular pattern on a radiograph of the femoral neck was analyzed. Measurements were taken along the compressive and tensile stress trajectories in the femoral neck. When the trabecular architecture changed, significant changes in the high frequency region of the power spectrum were detected. Quantitative processing was used to define parameters characterizing the trabecular architecture. Significant differences were found between the trabecular pattern in bones of normal subjects and in bones of osteoporotic patients.

The temperature of uncovered skin does not provide useful information about the blood temperature and blood flow. The information obtained from the same measurement for thermally insulated skin is more significant. In the present study, noncontact measurement of the temperature of thermally insulated skin was performed, using a teflon cylinder with an infrared fiber which was applied on the skin of the hand. The fiber transmitted part of the infrared radiation emitted from the skin to an infrared radiometer. Preliminary results show that thermally insulated skin temperature can be obtained from measurements of the partial radiation transmitted through the thermal insulation device which was applied to the skin, and that this temperature is related to tissue blood flow more than uncovered skin temperature.

Many animals, both marine and terrestrial, are sensitive to the orientation of the e-vector of partially linearly polarized light (PLPL). This sensitivity is used for navigation, spatial orientation, and detection of large bodies of water. However, it is not clear what other information animals may receive from polarized light. Natural light fields, both in the sky and underwater, are known to be partially polarized. Additionally, natural objects reflect light that is polarized at specific orientations. Sensors capable of measuring the characteristics of PLPL, namely partial polarization and orientation, throughout an image are not yet available. By placing 2 twisted nematic liquid crystals (TNLCs) and a fixed polarizing filter in series in front of a video camera, and by controlling the angles of rotation of the orientation of polarization produced by the TNLCs, we are able to fully analyze PLPL throughout a full image on a single pixel basis. As a recording device we use a small camcorder. The sensor can be operated autonomously, with the images analyzed at a later stage, or it can be connected (in a future phase) via a frame grabber to a personal computer which analyzes the information online. The analyzed image can be presented as a false color image, where hue represents orientation of polarization and saturation represents partial polarization. Field measurements confirm that PLPL is a characteristic distributed both under water and on land. Marine background light is strongly horizontally polarized. Light reflected from leaves is polarized mainly according to their spatial orientation. Differences between PLPL reflected from objects or animals and their background can be used to enhance contrast and break color camouflage. Our sensor presents a new approach for answering questions related to the ecology of vision and is a new tool for remote sensing.

Laser ((lambda) equals 0.630 micrometers , 1 - 3 mW/cm² with exposition 10 min) was used to investigate the influence of laser irradiation on rat platelet functional activity. It was determined that irradiation of thrombocyte enriched plasma caused increase of ADP-induced thrombocytes aggregation. Disaggregation process was not influenced considerably by this irradiation.

Four-hundred-forty-one nm and 1060 nm wavelength laser irradiation caused specific skin pain and warmth sensations. The reasons allowing skin pain sensations at the 441 nm laser irradiation and warmth sensations at the 1060 nm laser irradiation are discussed.

Results are described of recent contributions to the problem of optical scintillation in the atmosphere. Progress towards the solution of this very old problem is being made. It includes approximate modeling by means of numerical simulations, and simultaneous measurements of both laser intensity fluctuations and all relevant parameters.

The efficiency of tracking the random tilt variation of the wavefront in order to increase the average intensity with possible suppression of the intensity fluctuations is investigated. The analysis of the subject is suitable for both transmitting and receiving optical systems. The suggestion of a simple approximation for the tilt-corrected phase structure function allows us to reduce the integration order in the expressions for the statistical moments of the corrected field and to express them in the same form as those in the absence of the correction. Comparison of the results for arbitrary efficiency criteria of the correction demonstrates that the optimal conditions for fluctuation suppression and the increase of the average intensity at the recording point occur in different turbulent regimes. A significant fluctuation suppression is observed at a much weaker turbulence level as compared with the value corresponding to the maximum of the average intensity increase.

The features of a code for calculation of lidar returns from clouds are recalled. Some laboratory measurements on models showed the validity of the code with regard to polarization of received power. Reference is also made to a code for calculations of turbidity effects on optical systems.

The marine aerosol properties and thermal imager performance trial (MAPTIP) was conducted by NATO AC/243 Panel 04/RSG.8 and 04/RSG.5 in the Dutch coastal waters during the fall of 1993. The main objectives of the trial were (1) to assess marine boundary layer effects on thermal imaging systems and (2) to improve and validate vertical marine aerosol models with emphasis on coastal and near-surface effects. Aerosol and meteorological instruments, as well as thermal imagers and calibrated targets, were utilized on two off-shore platforms, a beach station, three airborne platforms, and buoy systems. This network of instrumentation has provided a comprehensive data base of aerosol size distribution profiles and relevant meteorological variables throughout the marine atmospheric boundary layer. Atmospheric turbulence and refractivity effects in the IR and rf bands were measured to assess the marine boundary layer effects on the degradation of thermal images. Thermal imagery in both the 3 - 5 and 8 - 12 micrometers bands was included to provide ground truth for assessing the low-level propagation effects near the ocean surface. Calibrated targets at different altitudes were observed to the maximum observable range under a wide variety of conditions. These data are to be used for the development and validation of IRST models and IR ship signature models, and for determining the effects of marine-generated aerosols, turbulence, and meteorological profiles on their performance.

A natural background consists of several thermal elements such as rocks, earth, soil, trees, etc. whose thermal diurnal behavior differs from each other. Individual properties such as the emissivity, thermal conductivity, heat capacity, etc. determine the influence of the surrounding environment on the surface temperature of these elements. However the surface properties are usually not known well enough to allow an analytical determination of the surface temperature. In this paper we present a simple thermal model which describes the surface temperature as a function of four meteorological parameters namely the solar irradiance, the long wave sky irradiance, the air temperature, and the wind velocity. Based on energy exchange processes that occur at the object-atmosphere interface a model is developed which gives a linear relation connecting the surface temperature to the above meteorological variables. Measured radiometric data along with simultaneous meteorological data is used to determine a set of five coefficients for each thermal element by means of a curve fit procedure. Examples of calculated and measured surface temperature curves are presented for two thermal elements namely a dirt path and a dry grass field.

In this paper incorporation of atmospheric aerosol and turbulence effects into visible and infrared search modeling is considered. Here, we show how the target acquisition probabilities and, conversely, the ranges at which targets can be detected are changed by the inclusion of atmospheric effects. It is assumed that images are contrast-limited rather than noise-limited, as is indeed the case with most visible, near infrared (IR) and thermal IR sensors of high quantum efficiency. For short focal lengths with low angular magnification, atmospheric effects on target acquisition are negligible. However, for longer focal lengths with large angular magnification, resolution is limited by the atmosphere and this has a strong adverse effect on target acquisition probabilities, times, and ranges. The considerable improvement possible with image correction for atmospheric blur automatically in real time is significant for contrast-limited imaging, and is discussed here too. Knowledge of atmospheric MTF is essential to good system design. It is also very useful in image restoration for any type of target or object.

Target acquisition methodology for infrared (IR) and visual man-in-the-loop imaging sensors has several limitations for many sensor performance assessment applications. Recent advances in computational vision modeling (CVM) have made dramatic improvements in the understanding of early human vision processes. A simple model of neural receptive fields consists of a generic image representation of the spatial processing characteristics for early vision cortical areas. The input image is first divided into its three color opponent components with each axis further decomposed into a set of band pass spatial frequency filters with different center frequencies and orientations. The spatial frequency decomposition is accomplished by an efficient encoding algorithm incorporating a hierarchical cascading Gaussian pyramid algorithm which is an alternating sequence of image output passing through Nyquist low pass spatial filter and subsampling local operators for image encoding. This paper examines the limitations of earlier target acquisition models and describes a computational model which starts with actual stimulus images as an input. It predicts human performance of experimental tasks by attaching a signal-to-noise ratio (SNR) to each spatial frequency channel, and then uses a combining function to define a composite d' parameter for a signal detection theory calculation of probabilities of detection and false alarm. Several examples of the model are applied to various detection applications.

There has been an increase in attempts to quantitatively measure `clutter' in the background of visual and infrared scenes; this parameter is crucial for determining the probability of detection of miliary targets in genuine battlefield conditions. In this paper, we analyze several clutter metrics by comparing the location of fixation points to the spatial distribution of the high areas of clutter. We determine that a strong correlation does indeed exist.

Wavefront sensors for adaptive optics measure the phase error produced by all layers of atmospheric turbulence. In doing so, they also measure the scintillation pattern in the aperture plane of the telescope for calibration purposes. However, scintillation can provide information about wavefronts in the higher atmosphere (7 - 10 km). This is because it is produced as Fresnel diffraction of high elevation turbulence. Scintillation can also be viewed as a laplacian of the same high altitude perturbations, when there is no middle level turbulence. Thus it can be inverted to yield these perturbations. Using this additional information, adaptive optics systems could correct for either low- or high-elevation turbulence (or both), and increase the field of view available for observation. The method is limited to high intensity and small size of the reference star, absence of middle level turbulence, and narrow spectral response by the detector.

Predictions of atmospheric transmittance in desert aerosol environments using MODTRAN code diverge significantly from measured data. Good prediction of the desert particulate size distribution is required in order to predict atmospheric scattering and absorption parameters. It is also essential to the prediction of the aerosol atmospheric modulation transfer function which is often the dominant component of the overall atmospheric MTF. Recently an effort to predict statistics but not size distribution according to simple weather parameters has been made for coarse desert aerosols. A quantitative analysis of the desert particulate size distribution models was also performed. In this research the size distribution parameters measured by optical counters are related to weather parameters. Known statistical and analytical models such as MODTRAN relate the size distribution parameters only to relative humidity for continental atmospheres. Although humidity has a significant role in the prediction of aerosol size statistics, other weather parameters are seen here to strongly influence also the size distribution parameters. Comparisons such as the above can be used to predict under which conditions the MODTRAN aerosol models have good or poor accuracy. It is also hoped that they will lead to improvements in MODTRAN, improving the accuracy of the humidity dependence as well as by incorporating other meteorological parameters into the MODTRAN prediction models.

The infrared and ultraviolet emission spectra of hydrocarbons and toxicants was measured and analyzed as compared to theoretical data at room temperature. Based on this data we constructed an electro-optical gas detector for monitoring low concentration of flammable paraffins, aromatics, and toxic hydrogen-sulfide. The optical method uses two wavelengths at several spectral bands: the signal and the reference which is sampled at a region where the hazardous gas does not absorb at all. Our apparatus is an innovative system that provides fast and reliable explosion detection at different lower explosion levels (LEL). As well, it can provide identification of low concentration of toxicants in the range of parts per million. The apparatus includes a fire detection option that can offer at the same time an automatic activation of fire suppression or neutralization system. It can detect paraffins in the range between 0.03 to 20 LEL per 1 meter by using the ultraviolet spectral band. At both regions the accuracy is about 20%. This open-path, line-of-sight gas detector can monitor and transmit an alarm signal prior to occurrence of fire or explosion.

The method of moments is used to investigate the interaction of a well focused laser beam with a step of a conducting surface. The two dimensional problem is solved by using a model of fictitious current filaments, while three-dimensional problems are treated by using a model of fictitious dipoles as the sources of the scattered field. Computer simulations indicate a difference between the two polarization components (TE,TM), but these differences are too small for practical measurements. The scattered field distribution is found to be highly dependent on the step height relative to the observation plane and on its position relative to the beam waist. Thus measurements of the intensity distribution in the observation plane can provide information about these parameters with high sensitivity. Experimental investigation confirms that step height, including its sign, i.e., hills or pits, as well as its position can be determined with an accuracy of about (lambda) /100.

The paper presents the study of dependences of parameters of laser-induced destruction of metallic layers against the layer thickness and parameters of the surrounding medium. The temporal behavior of the reflection, transmission, and absorption coefficients has been studied using oscillograms of the following laser pulses: incident, reflected, and transmitted through the target. Characteristic times of the destruction process have been evaluated.

Refurbishing worn machine parts by applying a new material to the eroded surfaces can be used with the aim not only to replace the worn out material but to obtain surface layers having better service characteristics than those of the original part. Infrared continuous CO₂ laser with a maximum power 9 kW was used in the investigation. The laser was equipped with an optical system and a computerized table that allows rotation of the specimen as well as its movement in three directions with a wide range of travel velocities. A direct injection of an alloying powder in the laser beam melted zone at the specimen surface was explored as a way of surface cladding. The powder used for this purpose was a cobalt-base alloy, `Stellite.' The thickness and composition of the clad layers vary significantly with irradiation conditions. A low content of iron (1%) in a clad layer indicates that a significant amount of Stellite powder can be homogeneously introduced. The absence of porosity or cavities in the clad layer as well as at the interface with the substrate was also shown.

In this paper the term microstructuring is used for two different tasks: (1) The growing of precise epitaxial layers by means of laser generated particle streams. This process may be treated as a laser assisted molecular beam epitaxy. (2) The lateral structuring of the layers by direct ablation with the help of focused laser beams. Up to now the application of lasers in thin film techniques mainly extended to relatively coarse processes like the formation of amorphous or polycrystalline layers on one side and the ablation in a micrometer scale on the other side. In both cases conventionally pulsed lasers, for example excimer lasers or Q- switched solid state lasers, are fulfilling the requirements. A different situation exists when complex semiconductor devices should be constructed. Here a monocrystalline epitaxial growing is absolutely necessary and the structuring needs a precise control of the ablation depths in the order of 100 nanometers or even less.

Scalar and vectorial photoinduced processes in films of chalcogenide glasses (ChG) As-S-Se- Te and Ge-S-Se-Pb systems are considered. Both irreversible and reversible highly resolving materials for recording and storage of optical information, sensitive in a wide spectral range, including the near infra-red region, are developed. The photosensitivity of some films can be increased 10³ - 10⁴ times when excitation is accomplished by very short intense laser pulses. The polarization information recording (reversible and irreversible) is fulfilled for some ChG films and is based on the phenomena of photoinduced linear dichroism and polarized photodoping of the films by silver. The application of the ChG films in systems of optical information recording, in holography, and in integral optics is discussed.

The paper presents the studies of laser-induced erosion of solid surface and, in particular, to determination of its energy threshold of damage. The studies are carried out by means of the technique of correlation holographic interferometry. Evaluations of the method accuracy are made. Preliminary experiments on energy threshold determination for aluminum surface are performed.

The electron beam lithography application to diffractive optical elements topology generation is examined. The formula for the estimation of exposure data volume for variable shaped electron beam lithography is presented as a function of diffractive optical element parameters and approximation accuracy. Special software was developed to prepare exposure data for diffractive optical elements fabrication. Diffractive optical elements with an artificial refractive index were manufactured with a feature size much less than the wavelength. Design and experimental results on photomasks fabrication are presented for an optical element focusing irradiation into a ring with ordered parameters. The photomask set was manufactured for reflecting optical element focusing high power CO₂ laser beam into two points with required parameters for laser welding.

Arrays of field emission micro-cathodes are the basis for massively arrayed electron beam lithography systems. We report on the fabrication of single crystal silicon field emitter arrays that have self-aligned extraction and focusing electrodes. By exposing a `capped' silicon pedestal to a lateral high temperature thermal oxidation, tips of uniform height and profile are formed, with radii of curvature typically less than 20 nm. The field emitters, the first level metal electrodes, and the second level metal electrodes are defined in the same optical lithography step and the first and second level metals are deposited during the same electron beam evaporation. In this fashion, both the extraction and focusing electrodes are formed simultaneously and are self-aligned to the field emitter. Sub-micron first level metal apertures and three micron second level metal apertures have been demonstrated using this process. The diameter of the second level metal electrode is determined by the optical lithography step. It is therefore possible to reduce the second level metal aperture by as much as 1.5 microns before necessitating the use of electron beam lithography. This process is suitable for fabricating self- aligned, second level quadrapole and octapole focusing electrodes.

Micro-optical elements, particularly microlenses, are finding growing application in different fields of modern optoelectronics. One of the most promising methods of microlens fabrication is based on photolithographic processes. Organic photoresists were used in the earlier development of microlens arrays. A new technique of microlens fabrication using inorganic chalcogenide photoresists is presented. Such photoresists have many advantages, such as very high resolution, photosensitivity in wide spectral range, high values of refractive index, transparency in the IR range, and the ability to be used as positive or negative resists depending on the developer used. These unique properties create new possibilities for the development of microlens arrays in the IR.

The use of a microlens on top of a photovoltaic solar cell working at high light concentration and the need for a very low absorption photoresist in the whole solar spectrum are explained. A process has been developed in a negative photoresist with adequate properties. The optical properties of the fabricated microlenses are described.

Conventional joint transform correlator (JTC) configurations are optimal with respect to noise tolerance only for input scenes embedded in white noise. Different processing should be devised in the presence of colored noise, taking into account the spectral characteristics of the noise. We hereby propose general, simple and powerful means, extending the capabilities of conventional JTC systems to enable Wiener filtering (WF) as well as parametric Wiener filtering (PWF) for patterns corrupted by colored noise. Noise is explicitly accommodated for by performing mathematical operations in between the two cycles of the JTC operation. The suggested JTC-based hybrid optoelectronic implementations do not necessarily rely on a-priori knowledge of the noise power spectral density, but rather determine an estimate of this distribution in an adaptive manner, based on measurable power spectra information. Such implementations provide great flexibility and real-time adaptivity to colored noise, resulting in improved correlation performance. Mathematical analysis and computer simulations are presented, whereby noise processes with different spectral characteristics and intensities are considered.

A particular form of the Gabor transform is optically implemented using a scanning Gaussian beam. The optical Gabor transform is then used to analyze the field diffracted by targets with features comparable to the wavelength of the incident radiation. Computer simulations and experimental results demonstrate that the optical Gabor transform is a powerful tool for the identification and measurement of wavelength and sub-wavelength features.

This paper describes the use of optics to enable collective communications between clusters of processors, within a `loosely synchronous' model of computation. In this model, phases of internal computation inside processors, alternate with phases of communication among processors. Collective communication, as in the new message passing interface (MPI) standard, means concerted action in a single command, e.g. shift of data from each processor to its right neighbor. Unlike previous work on general purpose optical implementation of given interconnects topology, that was concerned with providing only point-to-point communication, our work tries to provide services that improve programmability by the end- user. We are implementing a prototype with 3 clusters of 4 processors each, with an intra- cluster electronic crossbar. Inter-cluster communication is done via lasers transmitting message beams, which are suitably deflected in free-space to other clusters by means of acousto-optic devices. A typical collective communication comand is (multicast(source,Targetlist)), where the individual processors of the TargetList may reside in different clusters. Cluster addresses are encoded as acoustic wave input. Processor addresses are transmitted in the optical message headers, decoded at the detectors and redirected within the crossbar. The prototype itself and preliminary experiments are discussed.

A symmetric substrate mode holographic doublet that performs Fourier transformation is presented. This doublet is composed of two identical quadratic off-axis holographic lenses which were recorded on the same glass substrate. The first lens couples the light from the input into the glass substrate. The second lens, located at the back focal plane of the first one, couples the light out of the glass substrate and corrects the phase of the emerging wavefront in order to obtain the desired Fourier transformation. In such a configuration the input and the output planes are adjacent to the lenses, so the overall alignment is very convenient.

We investigated how best to record phase filters on a spatial light modulator (SLM) in a hybrid optic-electronic correlator that operates with incoherent light. The SLM used in our experiments was the Hughes liquid crystal light valve (LCLV), on which we recorded phase filters having 256 by 256 pixels. Two correlation configurations were tested in which the input scenes contained 512 by 512 pixels. In one, the input scene was introduced by means of a transparency that was illuminated by a laser beam that emerged from a rotating diffuser. In the other, the input scene was displayed on a miniature monochromatic cathode ray tube (CRT). The experimental results with both configurations reveal that real time updatability of optical filters for correlation with incoherent light is indeed possible. The analysis, correlation configurations and experimental procedures and results are presented.

A joint transform correlator (JTC) provides a real time correlation that is useful for pattern recognition. Based on the shearing interferometer configuration, a method for implementing a novel JTC is suggested. The obtained output correlation is spatially incoherent and thus provides better correlation peak quality. The proposed setup is characterized by its simplicity and stability and its ability to operate under real-time conditions. An experimental demonstration is given.

A novel two dimensional optical position sensor based on confinement of luminescence within a flat panel is described. The basis of the sensor is a flat luminescent panel, such as those used in luminescent solar energy concentrators. In these concentrators, a glass or plastic plate is either coated or impregnated with a fluorescent material. The incident radiation produces luminescent emission, much of which is confined within the plate through total internal reflection, and is thus guided to solar cells which line the thin edges of the plate. In order to use such a plate as a position sensor, four detectors are placed along two orthogonal axes at the edges of the plate, and the plate is illuminated with a spot of light. The spot of light induces luminescence, which is detected by the four detectors. The detectors' output is processed to provide position information. Position sensors based on the above idea were constructed, using both microscope slides coated with a fluorescent dye, and poly(methyl methacrylate) plates which were cast in the presence of a fluorescent dye so that they exhibited fluorescence throughout their volume. The results showed that the detector output varied monotonically with position. This paper presents the results obtained to date, together with a theory which relates the detector output to position. Suggestions for the improvement of the sensor, particularly in the areas of materials processing and sensor geometry, are provided.

Optoelectronic down-conversion of very high-frequency amplitude-modulated signals using a semiconductor laser simultaneously as a local oscillator and a mixer is proposed. Three possible constructions of a monolithically integrated down-converter are considered theoretically: a four-terminal semiconductor laser with dual pumping current/modal gain control, and both a passively mode-locked and a passively Q-switched semiconductor laser monolithically integrated with an electroabsorption or pumping current modulator. Experimental verification of the feasibility of the concept of down conversion in a laser diode is presented.

Simple, recursive ray-trace equations are presented that describe an exact ray propagation through a series of coupled confocal prolate spheroids.

Infrared horizon sensors are used for determining the orientation of satellites. These sensors usually operate on the principle of detecting the discontinuity in the infrared radiance at the limb. For calibration and testing of the horizon sensors under ground conditions, it is necessary to simulate the infrared horizon of the Earth. The simple, compact simulator described in this paper simulates the radiation of the Earth horizon and the shape of the radiance transition from space to Earth for the spectral range of the horizon sensor. This enables the sensor to be tested as a function of the altitude and orientation of the satellite. The simulator employs a spherical mirror; near its focal surface there are two radiating surfaces simulating space and Earth, respectively. Thermal contrast is obtained by controlling the temperature difference between the two surfaces. Calculated magnitudes of the spherical aberration of the mirror and disposition of the two radiating surfaces with respect to the spherical mirror are used for simulation of the radiance profile shape of the Earth horizon. This paper describes the structure of the simulator, the method of determination of its main parameters and experimental evaluation of the simulator characteristics.

Earth horizon sensors, used on satellites for determining orientation, usually operate on the principle of detecting the discontinuity in the infrared radiance at the limb. Most such sensors make use of radiant emission from the upper atmosphere in the 15 micrometers CO₂ absorption band and locate the 50% point on the horizon radiance profile, normalized to the maximum radiance value. Their accuracy is affected by errors due to seasonal, latitudinal, and random climatic variations in the shape of this profile. A method is presented for reducing the errors due to these variations, based on determining a specific profile shape which best fits the data obtained, and using this shape to estimate the position on the profile of a chosen tangent height. This method has been developed especially for a new type of static horizon sensor to be used in the Techsat-1 micro-satellite. This sensor gives a multi-point characterization of the profile, from which the shape can be ascertained and compared with a selection of representative profiles stored in the on-board computer. The profile best matching the data is then selected and used in the computation. The method could also be applied to those types of dynamic sensor which scan the profile with adequate resolution. The theory and application of the method is described together with computer analysis showing the degree of improvement in accuracy which can be achieved compared to traditional methods. It is shown that accuracies better than +/- 0.1 degree(s) can be obtained in low earth orbits.

We review recent research showing how significant asymmetry and optical nonlinearity (second harmonic generation) can be produced by injection of electric charge into dye/polymer blends. The mechanism for producing the nonlinearity is different from the usual dipolar alignment of the dye in an electrostatic field. Charge injection has been achieved by purely electrical means using `in-plane' electrodes, or photochemically, by irradiating a bilayer structure comprising a photoconductive layer and the polymer/dye layer.

A novel design for a linear beam steering module, based on diffractive elements, is presented in this paper. The steering module consists of two parallel gratings (with special chirped grating functions), where the input wave impinges on the first grating normal to the grating's plane. In the 0-state (no translation) the output wave emerges as a plane wave normal to the grating's plane. When the first grating is translated by an amount of (delta) x, the output wave is deviated by an angle of (Theta) , where the deviation ratio, (kappa) equals sin(Theta) /(delta) x, is a constant. This angular deviation can be easily converted to a linear scanning of a focused point, with the help of an appropriate focusing lens. In this paper, we use a novel design method that enables us to produce a beam steering device that does not suffer from any aberration. Specifically, the output wave emerges from the second grating as a plane wave, with diffraction limited performance, over the entire field of view. Moreover, the gratings can be fabricated with novel techniques that enable the manufacturing of the desired gratings in a mass-production line with relatively low costs. In addition, the system is small, compact, easy to work with and with a very large deviation relation. Hence, the desired translation can be accomplished using a small piezoelectric crystal that is attached to the first grating and there is no need to resort to expensive and complicated steering equipment.

The problem of focusing into an off-axis radial domain is reduced to the 1-D task of focusing into a segment. A new iterative method is proposed assuming the calculation of two 1-D Fourier transforms per each iteration and enabling us to generate diffractive optical elements (DOEs) intended for focusing into a radial off-axis focal domain. A phase calculated within ray-tracing approach was used as a starting point for iterative procedure.

A new design of a head up display (HUD) system, which incorporates a diffractive surface to enhance the performance of the system, is presented. The HUD is composed of three lenses, in comparison to a standard design of a similar conventional HUD which contains five spherical lenses. In addition to the advantage of compactness, the diffractive HUD has an improved performance over the entire field of view.

A 3' diameter refractive-diffractive element is presented. The element is used as a corrector in the optical system of a head up display at 545 nm. Average grating density of the design was 6 cycles/mm peaking to 10 cycles/mm. A 4 mask 14 level design was utilized, having a theoretical efficiency of 98.3%. The diffractive pattern was etched by RIE on a plano-convex fused silica lens, and then AR coated. Mask design and manufacturing process considerations are given and discussed. Tolerances and fabrication errors are analyzed. Micron mask misalignment and duty cycle errors, etch depth error of +/- 5%, and +/- 6% uniformity were achieved over the entire area, yielding a total efficiency of the element of > 96%. Diffraction measurements were made and compared to the theoretical calculations. The design and fabrication results prove diffractive elements in the visible a viable solution to correct aberrations in high quality optical systems such as head up displays.

Narcissus is usually approximated by means of a paraxial ray trace through the optical system in the ordinary direction of light travel. An accurate calculation involves tracing real rays backwards from the detector to the reflecting surface, and back to the detector after reflection. It is shown that the diffractive order of maximum efficiency for a diffractive optical surface is different for transmitted and reflected radiation. This precludes the use of the paraxial approximation for calculating the effect of narcissus. The real ray method of calculation must be used with specific orders of diffraction based on their efficiencies.

In this paper, we consider the measurement of modulation transfer function (MTF) by means of spatially random, noise-like targets. We begin our discussion with the concept of shift- invariance and the measurement of MTF in pixelated systems. We then proceed to the methods for generation of these noise targets, using both laser speckle and transparency-based techniques.

Surface roughness of sections of hollow waveguides is examined by measuring the backscattering reflection and using the total integral scattering (TIS) method. The iodination of silver was found as the main factor affecting the surface roughness. The AgI layer thickness also affects an interference phenomena as a function of wavelength.

Segmenting of the incident wavefront at the entrance pupil of an optical system, occurs in systems with segmented windows and in certain configurations of scanning systems that include polygons as the scanning element. Segmenting of the wavefront may cause a serious degradation to the MTF of the system. In some cases, the resolution of such systems may be decreased by a factor of two. In this paper, the degradation of the MTF is calculated for coherent and incoherent light. It is shown how such cases may be simulated using the CODE- V^R software. An experimental setup was performed in order to demonstrate the incoherent case and its results are presented.

The manufacture of optical elements is an international business, but communications between optical designers and optical manufacturers have been hampered by the lack of generally accepted standards for documenting optical design data. Most commercially available optical design programs utilize ad hoc proprietary routines to apply output data for manufacturing. This places the burden of interpreting the output on the manufacturer, who may not use or even be familiar with the program that produced the data. With the increased use of optical systems that include elements manufactured all over the world, the need for standard documentation of optical manufacturing data is greater than ever. The ISO 10110 drawing standard, now in its final stages of approval, should improve the current situation. It provides standards for the preparation of optical element drawings, discussion of testing and measurement procedures that are implicit in the data specified in the drawings, and recommendations for the format of data used to describe optical surfaces. As a step to aid the acceptance of the standard, we have adopted the recommendations of ISO 10110 for the output of optical element drawings in our OSLO programs for optical design. In addition, we have adopted the recommendations of the standard for specifying aspheric surfaces, and for default tolerances.

An optical resonance phenomena, based on an interference effect that occurs when a plane wave is incident on a dielectric grating/waveguide structure, is presented. The incident wave excites a guided mode in the waveguide which in turn is partially diffracted by the grating in the direction of the transmitted zero order beam, interfering destructively. As a result most of the light energy is contained in the reflected zero order beam. This resonance phenomena is explained with a ray picture of the multiple interference and analyzed by solving Maxwell's equations for the exact eigenfunctions in a grating/waveguide structure. Some basic structures have been fabricated and experimentally tested. The results reveal that the resonance beamwidth and bandwidth depend strongly on the parameters of the grating/waveguide structure. Measurements indicate that the bandwidth of the resonances can be as narrow as 1 nm, with a corresponding angular beamwidth on the order of minutes of arc.

The far-field patterns of two types of nonimaging concentrators were studied experimentally both in the visible and in the infrared. The input beam was a diffuse light generated by a black-body source, with a well-defined divergence angle. Several new features were observed, and were explained with a simple model based on geometrical optics.

In this work we propose a design procedure for producing an optical interconnection lens as a computer originated hologram. New methods for analyzing and designing holographic optical elements are developed. These are mainly based on the introduction of Taylor series expansion to solving the equations of holographic elements. Specifically, the Taylor expansion is exploited to solve the Bragg conditions after they are reformulated as a nonlinear partial differential equation. The expansion is also used for analyzing the propagation of a given wavefront in an optical system that can be comprised of several holographic and conventional elements. According to computer simulations, the spot size, calculated in accordance with geometrical optics, is several orders of magnitude less than the diffraction limited size, and the diffraction efficiency degradation is less than 0.01%.

A novel method for controlling the chromatic aberration of kinoforms is described. The method is based on the superposition of a few kinoforms, each of which is designed for one specific wavelength. This approach can be useful for applications where elimination of chromatic aberration is necessary (for example CO₂ and HeNe lasers in surgery), as well as for applications which are based on color separation (e.g. multicolor or thermal detection).

Optical fibres are well established in the domain ofpoint-to-point telecommunications, where they demonstrate the advantages of very wide bandwidth, low attenuation, low weight and cost, and immunity to electromagnetic interference. Passive fibre components, such as fourport couplers for signal distribution or wavelength multiplexing, have emerged allowing increased exploitation of the available bandwidth or application in local-area networks and all-optical signal processing circuits. The advent of special amplifying fibres has provided transmission over effectively lossless channels, and has further driven the development of many peripheral passive components. Examples are fused-fibre couplers for amplifier pump multiplexing, fibre gratings for pump filtering or suppression of amplified spontaneous emission (ASE), and inline isolators to allow high gain and reduced gain ripple. Complementing advances in fibre amplifiers are fibre lasers that can convert poor-quality light from semiconductor devices into low-noise, single-frequency sources with the potential for broad tunability and high output power.

High sensitivity, ring-type measurement devices based on acousto-optic and fiber-optic delay lines are described. Applications of these devices for linear and angular displacements with resolution of 0.1 micrometers and 1 (mu) rad are shown. Methods of further improvement of the devices' characteristics are discussed.

The devices are based on the dependence of refractive index on electric field. The device for angular measurements consists of a number of integrated optics interferometers that are situated around a ring. There is a metal plate under the interferometers. Above the reference beam of each interferometer there is an unmoving conducting plate; above the other beam there is a moving conducting plate attached to the object undergoing rotational motion. The size of the moving conducting plate is a little more than the size of an interferometer. Each of the plates has its own constant voltage, which is supplied by a voltage source. As the metal plate rotates with the object, the signals of neighboring interferometers change in a sinusoidal way, with a phase difference of (pi) /2. The magnitude of the angle of rotation of the metal plate, and thus of the object, can be calculated using the signal from the interferometers by using an appropriate algorithm. The device for linear measurement has a similar structure.

Temperature variations affect pumping efficiency, spectroscopic properties of lasing ions, and physical parameters of the host material. A numerical model was developed for evaluation of multilevel solid-state lasers. The model accounts for atomic levels population variations during Q-switched pulse evolution and for temperature dependence of the lasing transition linewidth. Results of simulation of pulsed Nd:YAG laser are presented for various temperatures of the laser crystal. The results of the simulation are compared with experimental results obtained using a Neodymium:YAG laser which is Q-switched by crystalline and organic saturable absorbers. The observed behavior of the lasers is in good agreement with the theoretical prediction.

We have designed a Nd:YAG laser to be pumped by the High-Flux Solar Furnace (HFSF) at the National Renewable Energy Laboratory. Based on the unique features of the HFSF, the design objectives are high brightness and superior efficiency in primary mirror area utilization. The HFSF has a primary mirror of 11.5 m² and a 1.85 f-number. With such a high f-number, the target is set off-axis and does not block incoming solar flux. Moreover, large f-number enables concentration which approaches the theoretical limit, and a two- dimensional non-imaging concentrator deposits the solar flux onto the internal part of a 10 mm diameter laser rod. For high brightness, we plan a wide low-loss fundamental mode and a laser rod aperture that suppresses high order modes. To get a fundamental mode, of up to a 2.5 mm waist, we have designed a convex-concave resonator, following well-known g₁g₂ equals 0.5 design for resonators with internal beam focusing. We have used the edge ray principle to design the concentrator, and ray traced the deposited power inside the laser rod. A 1.3% Nd doping level supports a maximal power deposition inside a 5 mm diameter.

Single longitudinal mode solar pumped Nd:YAG ring cw and Q-switched lasers were simulated, built, and tested. The concentrator and laser designs, polarization control, and output coupling for cw and long pulse generation are presented. Laser pulses duration of 500 ns were measured supporting the single longitudinal mode operation with the linewidth of 2 MHz. This solar laser is proposed for remote sensing of the atmosphere from the outer space, namely the global wind measurement.

Our new, scalable disk laser concept allows efficient diode-pumped high-power operation of quasi-three-level lasers with high beam quality. The use of a very thin crystal disk with one face mounted on a heat sink together with the low heat generation of Yb:YAG (< 11%) enables high pump power densities (> 5 kW/cm²) required for efficient operation without strong thermal degradation or optical distortion. Compact diode-pumped solid-state lasers in the kilowatt range seem to be achievable by increasing the pump beam diameter and/or by using several crystal disks. We present our latest results, obtained with a (phi) 2 mm X 0.4 mm Yb:YAG crystal operated at temperatures between 200 K and 300 K with an output power of up to 13.5 W and more than 50% optical-to-optical efficiency at 9.5 W. Simulations of thermal deformation and stress as well as of efficiency are also presented. Additionally, recent measurements of the tuning range of the diode-pumped Yb:YAG-laser, indicting the potential of femtosecond pulse generation, are shown.

A new technique for combining two diode laser beams to a laser rod is demonstrated. By taking advantage of the two absorption peaks of Nd:YAG around 795 and 809 nm, and of Nd:YLF around 794 and 807 nm, a dichroic mirror was used as the combining element of two diode lasers lasing at different wavelength at room temperature. Using an end-pumped geometry, an oscillator pumped by two 2 W diode lasers (SDL - 2372-P1) was built. In the free-running mode of operation, total light to light conversion efficiencies of 26%, 29%, and 31.5% with 0.31, 0.32, and 0.35 slope efficiencies were achieved for Nd:YAG pumping with the 795 nm, 809 nm and the two diodes together (with a total of 4 W), respectively. In the case of the free-running Nd:YLF the total light to light conversion efficiencies were 33%, 26%, and 31% with 0.41, 0.33, and 0.36 slope efficiencies, for the same pumping situations. For q-switched operation and pump pulse width duration of approximately 1 fluorescence lifetime the Nd:YAG efficiencies were 10%, 11%, and 13%, and for Nd:YLF 11.5%, 10%, and 10.5%, for the same pumping cases. Using this coupling scheme the output of the laser was effectively doubled. The beam quality was approximately 1.1 diffraction limited in all cases. This technique is suitable for pumping other lasing materials such as Nd:YVO₄ and Nd:BEL around 800 nm, and Cr:LiSrAlF₆ around 680 nm.

The end of the eighties saw the beginning of the production of high-power industrial CO₂ lasers in Bulgaria. A research team at the Institute of Informatics of the Bulgarian Academy of Sciences designed a series of modules for automated control and stabilization of the output parameters of the industrial CO₂ lasers with longitudinal flow. The present article deals with the maintaining of optimum temperature regime as one of the main factors for the stable functioning of these lasers.

Performance of lasers has been steadily improving, due in part to the availability of electronic beam diagnostic instrumentation. This instrumentation enables laser designers and users to obtain illuminating and quantitative information about the beam intensity pattern. Armed with more precise data on the beam profile, designers are able to make dramatic improvements in the beam uniformity. Advances in this critical instrumentation are discussed.

I propose new schemes for pumping of non-standard N₂O lasers which can be useful for generation of short laser pulses in 8 micrometers region.

I.A.I.'s Precision Instrument Industry division (TAMAM) has developed a tactical grade ring laser gyro (RLG). The gyro, which is only 3 cm long per leg, triangular shaped, has been developed for application of moderate performance (stabilization, control, low/medium accuracy navigational systems), where small size and weight are of a particular importance. The gyro is characterized by a bias of better than 0.5 degree(s)/h and scale factor stability better than 200 ppm over a dynamic range of at least 500 degree(s)/sec. It has been tested over a temperature range of -35 degree(s) to 90 degree(s)C, 16.8 g rms vibration and over 100 g shock levels.

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 in part 1, 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 meteorological 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 bit error rate under certain conditions is possible with the new adaptive system model.

Decrease in signal to noise ratio and maximum bit rate, as well as increase in error probability in optical digital communication are caused by particulate light scatter in the atmosphere and in space. Two effects on propagation of laser pulses are described: (1) spatial widening of transmitted beam and (2) attenuation of pulse radiant power. Based on these results a model for reliability of digital optical communication in a particulate scattering environment is presented. Examples for practical communication systems are given. An adaptive method to improve and in some cases to make possible communication is suggested. Comparison and analysis of two models of communication systems for the particulate scattering channel are presented: (1) transmitter with high bit rate and receiver with avalanche photodiode and (2) transmitter with variable bit rate and a new model for an adaptive circuit in the receiver. An improvement of more than seven orders of magnitude in error probability under certain conditions is possible with the new adaptive system model.

This paper describes the design and implementation of a pulse position coding module which constitutes one of several building blocks in the chain of an ISDN-to-IR transmission interface. This interface provides the suitable adaptation of ISDN (basic access rate) to the IR link requirements. The development of such an interface stems from the requirements of factory and office communications using wireless terminals based on diffuse IR radiation, along with the utilization of the inherent capabilities of ISDN.

In the past, an emphasis was placed on the research, design, and development of various infrared (IR) devices and systems primarily for military applications. The future trend, however, is towards the use of IR technology equally or with greater emphasis in the commercial sector. Both indoor and outdoor applications are possible. Commercial availability of special solid state diodes has opened the possibility of producing cost-effective laser atmospheric communication applications, for voice, data, and video. It is expected that infrared communications technology as a photonics field will have the impact of the major photonics field in the 21st century.

We review the advantages of digital pulse-position modulation (PPM) for wireless infrared communications, and then examine several equalization strategies for detecting PPM signals in the presence of intersymbol interference and additive white Gaussian noise. Our approach is based on an equivalent vector channel, obtained by viewing PPM as a binary block code, and we use this vector channel to derive the ML sequence detector. We also propose three sub- optimal block-by-block detectors, all of which use block decision-feedback equalization (DFE) to mitigate inter-block interference but differ in how they mitigate intra-block interference: the ML-BDFE accounts for it in an optimal way, the comparator-BDFE uses linear equalization, and the correcting-scalar-DFE uses DFE. We illustrate low-complexity implementations of these equalizers, and compare their performance to the ML detector using Monte-Carlo simulations.

Cross campus inter-building connectivity is a common requirement in industrial and university sites worldwide. The common solutions include modems and leased lines, however, these solutions are expensive. The problem is, therefore, a classic challenge for the emerging area of wireless networks. The UWIN (Universal Wireless Infra Red Network) is a pioneer solution in the field. In this paper the applicability of this novel solution to a real world problem is demonstrated. The optical and systems design issues are involved in its implementation in Ethernet, Token Rings and FDDI are discussed.

Image blurring due to sensor motion can often be the limiting factor in the resolution of the picture and, hence, on our ability to detect targets. In a recent paper, we've proposed a method for the restoration of such images; good results have been obtained. In this paper we propose to quantitatively evaluate the effect of such a restoration process on automatic target acquisition. A method is derived to determine the probability of detection for targets which have been blurred by sensor motion. This method is then applied to restored and non-corrected pictures. The degree to which such real-time restoration is worthwhile is discussed.