Advanced coal-fired power generation systems, such as pressurized fluidized-bed combustors and integrated gasifier-combined cycles, may provide cost effective future alternatives for power generation, improve our utilization of coal resources, and decrease our dependence upon oil and gas. When coal is burned or converted to combustible gas to produce energy, mineral matter and chemical compounds are released as solid and gaseous contaminants. The control of contaminants is mandatory to prevent pollution as well as degradation of equipment in advanced power generation. To eliminate the need for expensive heat recovery equipment and to avoid efficiency losses it is desirable to develop a technology capable of cleaning the hot gas. For this technology the removal of particle contaminants is of major concern. Several prototype high temperature particle filters have been developed, including ceramic candle filters, ceramic bag filters, and ceramic cross-flow (CXF) filters. Ceramic candle filters are rigid, tubular filters typically made by bonding silicon carbide or alumina-silica grains with clay bonding materials and perhaps including alumina-silica fibers. Ceramic bag filters are flexible and are made from long ceramic fibers such as alumina-silica. CXF filters are rigid filters made of stacks of individual lamina through which the dirty and clean gases flow in cross-wise directions. CXF filters are advantageous for hot gas cleanup applications since they offer a large effective filter surface per unit volume. The relatively small size of the filters allows the pressurized vessel containing them to be small, thus reducing potential equipment costs. CXF filters have shown promise but have experienced degradation at normal operational high temperatures (close to 1173K) and high pressures (up to 24 bars). Observed degradation modes include delamination of the individual tile layers, cracking at either the tile-torid interface or at the mounting flange, or plugging of the filter. These modes may be attributed to a number of material degradation mechanisms, such as thermal shock, oxidation corrosion of the material, mechanical loads, or phase changes in the filter material. Development of high temperature optical fiber (sapphire) sensors embedded in the CXF filters would be very valuable for both monitoring the integrity of the filter during its use and understanding the mechanisms of degradation such that durable filter development will be facilitated. Since the filter operating environment is very harsh, the high temperature sapphire optical fibers need to be protected and for some sensing techniques the fiber must also be coated with low refractive index film (cladding). The objective of the present study is to identify materials and develop process technologies for the application of claddings and protective coatings that are stable and compatible with sapphire fibers at both high temperatures and pressures.

In the present paper it is shown that the magneto-optical (MO) bismuth-substituted bubble garnet films are attractive for Paraday magnetic field (current) sensors with the rise time about 10 ns. This problem can be solved if the sensors are based on the films with domain wall velocity up to 1000 rn/s and. domain wall mobility about 10 rn/Cs Oe) or more. Using high-speed photography method the two kinds of materials with the high dynamical parameters were studied: 1) (111)-oriented (Tm,Gd,BiL(Pe,Ga)O10 films with high gy- romagnetic ratio ; 2) (21O)-oriente (Y, Lu,r,i) 3(Pe, Ga) 512 films with orthorhombic anisotropy.

Several types of magnetooptical (MO) media, possessing "memory" effect are discussed for the purpose of thermal sensing. These are high coercive garnet films, trad.itionaly used. for therrnoxnagnetic re- cording, films with configurational phase transitions between dife- rent types of the domain structure produced by local heating and films with artifially formed pixel arrays. It's shown that structures of the latter type are most suitable for thermal sensing.

It will be shown that a quartz crystal coated with single strand DNA can act as a sensor for hybridization in liquids. The method used is based on the change in oscillating frequency resulting from the increase in mass on the crystal surface which is accompanying the hybridization. Specifically, it will be shown how an AT - cut quartz crystal oscillating at 5 MHz would operate as a DNA probe. Also a theoretical model will be presented which will show what the key physical parameters are, their interrelationships as well as their effect on measuring the inimobilization of DNA on a piezoelectric crystal.

Scatter from beryllium mirrors often seems to be higher than expected based on mirror surface foughness data. The paper verifies the effects and shows that in addition to surface topography scatter is caused by mirror defects that are non-topographic in nature (subsurface flaws, optical contant variations across grain boundaries, etc.). This effect is more severe in them id IR than the visible because non-topographical scatter tends to scale as inverse wavelengths for several materials is presented and analyzed. Beryllium is found to be especially prone to these problems. The conclusion is reached, that a profile (or roughness) requirement is not sufficent speciefication to achieve low scatter space mirrors.

A new method for accurate determination of refractive index, 'n' and gecznetrical thickness 'd' of any optical layer of a multilayer syst En the presence of preceeding layers [s developed En which, making use of measured reflectance and/or trannittance over a spectral range , ' n' and 'd' are evaluated through a closed loop nunerical fterati. It [s seen that the method can be applied to any nvltilayer systn, irrespective of the nature of the layer under investigation, thin or ultra-thin, low or high refractive index films. The accuracies of 'n ' and ' ' are in general better than 0 .01 and 10 A0 respectively. The method is successfully applied to determine the layer pararreters of a typical four layer non-quarterwave antireflecti (AR) coating.

A dual stage, closed loop and self scanning algoritFin has been proposed for precise determination of optical constants i.e., refractive index, 'n', and absorption Index, 'k ' , together with thickness ' of thin film coatings . In the first stage , refractive index solutics over a knc.zn range are generated for a given set of nasured paranters , nanely,reflectance, R and trannittance , T, and preset thickness of the coating , where as in the seccd stage a merit function, defined in terms of mean square of the difference between refractive index values at consecutive wavelengths, is miriimised with respect to thickness. It is seen that while the algorithn can estimate the 'n ', ' and 'd ' to an accuracy better than 0.005, 0.002 and 5/50 A0 (5 A0 for visible region coatings and 50 A0 for infrared coatings ) for an experinntal error of +0 . 005 in R arid T and it is able to overccme the ambiguity of ns.iltiple solutions, inherent in the existing methods. Apart from this, the required data can be generated faster, dispensing the cunbersane and expensive graphic systems. The algoritFin has been successfully appiied to determine the optical constants of absorbing and transparent films.

Composite media are widely used in aeronautics, aerospace and electronics. We intended to make a modeling of their microwave properties. An overview of main effective theories is proposed, associated with comparison between theoretical and experimental results. This leads to determine limits of these models used for composite media. Several experimental data show the influence of the size distribution of the particles, probably due to a more complex interaction between the resin matrix and the embedded indusion. To describe this, we propose to make use of extended Sthvola's particle multilayered model.

The calculation of the effective permittivity and permeability of artificial dielectric materials requires the calculation of the dipole moment of the particles embedded in the binder. This paper addresses the problem of efficiently finding the dipole moment of nonspherical particles by various numerical methods. The conjugate gradient method is shown to hold promise as a practical technique for implementing the macromolecular model of such particles.

In this paper we examine the role of chirality on electromagnetic wave propagation in discrete random chiral composites. The composite is modeled as effectively chiral even though the medium is not chiral. The inclusion phase is randomly distributed and is associated with a chiral material constant (meters) which exists due to the handedness of the material. The effect of this parameter on the propagation of the em wave in an effectively chiral medium is examined.

In this per, we present a modified four flux model in which multiple scauering among particles is included. If the incident radiation is diffuse in nature, the model can be easily converted to a two flux one. On the optical side, the modified flux model can find various applications, for example, tailoring the opacity of paint materials, designing the antireflection coatings, and predicting the color of a ceramic glaze.

The distributions of the field strength as well as of the energy flux in the vicinity of a small particle excited by an electromagnetic radiation are investigated. Analytical expressions of angular distribution of the energy flux are given. Numerical results are presented for the case of a single alumina particle suspended in air.

We have set up a state of the art free space measurement system for characterizing the electromagnetic reflection and transmission properties of planar samples in the 5-100 GHz frequency range for both normal and oblique incidence. The key components of the measurement system consists of two spot-focusing antennas mounted on circular tracks on a horizontal table, mode transitions, coaxial cables and a HP851OB network analyzer. The system is fully automated and has been calibrated to yield reliable and accurate values of free space S-parameters of planar samples. The complex electromagnetic properties (e. g., complex permittivity, complex permeability, etc.) of the sample can be measured as a function of frequency. The experimental results for teflon, a microwave ceramic material and silicon rubber-carbonyl iron composites are presented. Measurements can be done in a non-destructive and non-contact mode, that also permits material characterization under high temperature conditions.

Electromagnetic waves can discriminate between objects of different handedness due to their transverse nature, which implies that the origin of chirality need not necessarily be molecular as in the case of optically active media. Effectively chiral composites may, therefore, be constructed by embedding chiral microstructures in non-chiral host media. Chiral polymer coatings for microwave applications consist of chiral inclusions dispersed in a dielectric matrix material. In our laboratory, chiral polymer coatings are realized by embedding a large number of miniature metal helical springs in a lossy polymeric material or by randomly dispersing microballoons filled with a chiral polymer in a lossy host material. Absorption and shielding are considerably enhanced due to the increased multiple scattering and subsequent absorption in the host material. An attractive application of chiral composites is as a broadband microwave absorber. In this paper, we will investigate the reflectivity reduction characteristics of chiral polymer coatings by changing the dielectric characteristics of the matrix material.

La i xSrxCoO3 (0, 0.3) were prepared by two solution methods using water and hexanoic acid as solvents, respectively. The single phase of LaCoO3 was obtained at 600CC the case of hexanoic acid route, which was about 300'C lower than in the other case with water alone. It was possible to make thin films of the perovskite compounds by controlling the viscosity of the hexanoic acid solutions. These perovskite materials are expected to have applications as oxidizing catalysts in automobiles, as electrodes for zirconia heaters and as cathode materials for C02 lasers.

The possibility of monolithic integration of microwave magnetic and semiconductor electronic components has been investigated by growing spinel ferrite films on GaAs and Si using the spin-spray plating (SSP) technique. Since film deposition by SSP is performed at temperatures as low as 100 C, this process facilitates deposition of ferrite material without any thermal deterioration of the underlying GaAs devices. This was demonstrated by depositing and patterning a Ni-Zn ferrite film on a portion of a GaAs wafer containing several MMIC circuits. X-ray diffraction analysis of SSP-grown ferrite films indicated that the films formed different crystallographic textures at different growth temperatures. To achieve the thicker films required for practical device applications, deposition of a 25-pm-thick Ni-Zn ferrite film was demonstrated by a multiple deposition method with intermediate drying processes. The magnetic properties of these films, measured by ferrpmagnetic resonance (FMR) , compared well to those of commercially available polycrystalline material. The electrical resistivity of the films varied as a function of their chemical composition. The dielectric loss tangent (tan 5) of the as-deposited film was observed to be greater than ten. However, the measured resistivity dependence of dielectric loss tangent showed that the dominant microwave loss mechanism was not due to conduction alone. Post-growth annealing experiments indicated that moisture in the films trapped during the SSP process caused high dielectric losses, and that annealing could reduce the loss tangent value.

Recent research on ferroelectric films via the sol-gel method is discussed, with emphases on preparative problems, electrical and optical properties, and applications in devices. Ferroelectric thin films, including LiNbO3, BaTiO3, KNbO3, Pb(ZrTii)O3, and (SrBai..)Nb2O6, were investigated. The structures of these ferroelectric materials are primary made up of networks of oxygen octahedras. They crystallized at relatively low temperature (< 0.5 Tm ), where Tm is liquidus temperature. Typical applications of ferroelectrics considered here include holographic memory and non-volatile semiconductor memory devices.

A conductive polymer composite of 2.4 mm thickness has been measured at a frequency range of 100 MHz to 18 GHz. This sample was measured for its EMI and EMC characteristics for use in electromagnetic shielding applications. It was shown that this thin sample achieved high transmission loss over a broad frequency range.

The scope of this research effort centers upon investigating the performance of few-mode, elliptical core (e-core) fibers as strain sensors in composite structures. Primary concerns for the development of such sensors depends upon the assured survivability of the fiber coating during composite cure and the efficient transfer of matrix stresses to the fiber. In previous work, high temperature polyimide coatings for embedded optical fiber strain sensors were examined in this regard. The objective of our current research effort is to characterize the performance of an e-core fiber for sensing strain within cured test coupons of commercially available composite prepreg materials. In these investigations, single, uncoated e-core fibers were placed into graphite/epoxy prepreg material. Test coupons were then processed via the standard protocols for cure. Embedded e-core/composite specimens were examined under controlled tensile and bend conditions. Changes in optical power output were correlated to the mechanically-induced strain on the sample. Memory effects upon optical power output related to strain sensing, indicative of possible matrix/optical fiber debonding, were also investigated.

In recent years, the strong demand on high-performance structures has driven the development of "smart" materials and stractures. Piezoelectric smart stri.ictures composed of passive elastic materials and active piezoelectric materials are developed recently and they seem to be very promising in a variety of engineering applications. In this paper, a new piezoelectric thin-shell vibration theory is proposed and the system electrodynamic eqtations of piezoelectric shells are formulated vising Hamilton 's principle and piezoelectricity theory. General electric and mechanical boundary conditions are also derived. The proposed piezoelectric shell theory is very generic, which can be simplified to account for many other commonly occurred geometries, such as spheres, cylinders, plates, cones, etc. Simplification of the generic theory to two plate cases (thin and thick) is demonstrated in a case study.

Active smart" space and machine structures with adaptive dynamic characteristics have long been interested in a variety of high-performance systems, e.g., flexible robots, flexible space structures, "smart" machines, etc. In this paper, an active adaptive structure made of piezoelectric materials is proposed and evaluated. The structural adaptivity is achieved by a voltage feedback (open or closed loops) utilizing the converse piezoelectric effect. A mathematical model is proposed and the electrodynamic equations of motion and the generalized boundary conditions of a generic piezoelectric shell subjected to mechanical and electrical excitations are derived using Hamilton's principle and the linear piezoelectric theory. The dynamic adaptivity of the structure is introduced using a feedback control system. The theory is demonstrated in a case study in which the structural adaptivity (natural frequency) is investigated.

This paper presents an integrated solution that combines an inexpensive optical sensor and a piezoelectric-actuated micro-motion manipulator to enable precision sensing of the end-effector position with respect to the workpiece directly. The materials presented in this paper are built on the author's prior research on sensing and actuator1'2'3. In particular, this paper highlights the sensor and actuator needed for integrated robotic motion control in flexible manufacturing environment. The optical sensor is based on the concept of retroreflective vision sensing to locate workpieces or end-ofarm tooling, which requires no priori knowledges of object reflectance properties. The design of a piezoelectric actuated micro-motion mechanism to enhance the resolution and to provide an effective means of end-point sensing using microbending losses in fiber optics is addressed.

This paper reviews theoretical and test results for the development of piezoelectric actuator based - active vibration control (AVC). The evolution of this new technology begins with an ideal model of the actuator and progresses to a more sophisticated model.

Collocated sensors and actuators offer significant robustness and design benefits in distributed parameter vibration control. It is shown that sensors and actuators are collocated in this sense when they are both physically coincident and their spatial derivative orders are equal. These requirements are expressed more generally as an integral equation that constrains the transducers' "modified" spatial distributions. Distributed parameter collocation is demonstrated by a transducer placement study for a nondimensional cantilever beam. The first configuration uses two disthbuted piezoceramic actuators and two accelerometer sensors. This combination typically leads to input/output frequency response functions having slow nonminimum phase transmission zeros and poor singular value frequency response characteristics, with high sensitivity to placement. The problem is exacerbated when the accelerometers and distributed actuators are "collocated". The second configuration uses two distributed piezoelectric actuators, now combined with two distributed strain gage sensors. When these equivalent-order distributed transducers are collocated the resulting frequency response matrices are strictly minimum phase, and have desirable singular value characteristics determined solely by the actuator placement's coupling into the beam's modal curvatures. These characteristics are maintained for small strain sensor apertures centered over larger actuator apertures, including some misalignment, for low frequencies. A generalization is developed to facilitate the collocation of transducers having dissimilar spatial derivative order.

There is a growing interest in the use of distributed actuators and sensors for the active vibration control of thin plates. Recent efforts in this area have been resthcted to the control of plates with cantilevered boundary conditions. This paper presents an energy based analysis of distributed transducer design issues related to the observation and control of thin plates applicable to more general boundary conditions. The particular class of distributed transducers is limited to those which are separable in space and time, i.e. degenerate distributed transducers. The analysis exploits plate mode symmetry and boundary integral representations of key parameters to choose appropriate spatial weiglitings for distributed sensors and actuators. The technique may be used to simultaneously control multiple plate modes as well as target selected modes. While the results presented here are applicable to a broad class of distributed transducers, for the purposes of illustration models based on the piezoelectric polymer film polyvinylidene fluoride (PVF2) are used.

The composite smart skin approach to airborne structures advances the capability of monito ring and controllingforces acting upon the structure. These capabilities include the ability to characterize and control the external boundary layer condition acting upon the structure, control of internal vibrations as causedfromforces acting upon and within the structure and damage localization along the structure. The inclusion of the smart skins, and hence the localization for control, is within the composite air wings of the airborne structure. With the advent of composites as the fabrication material ofchoice in recent airborne structures, newproblems result in the composite structure from forces offlow znd vibration. Additionally, damage within these composites is dfflcult to realize and can potentially lead to criticalfatigue conditions throughout the structure. The smart skin approach offers the potentialfor early warning and control over such problems.

We report our investigations of multiple-beam optical limiter configurations using GaAs and Si as the nonlinear optical material. Three distinct multiple-beam geometries are discussed. One of these, in which two beams interfere within the semiconductor, takes advantage of transient energy transfer and photorefractive beam coupling to deplete the signal beam. The other two configurations exploit the absorptive and refractive index changes induced in the semiconductor by a strong control beam that arrives at the sample before the signal. For one of these configurations, nonlinear absorption and induced defocusing are used to attenuate the signal in the other, nonlinear absorption and induced deflection are used. We discuss the relative merits of each configuration and compare them to single beam results obtained under identical experimental conditions.

We describe picosecond single- and multiple-beam measurements of the nonlinear absorption and refraction in a variety of semiconductors. Single-beam and pump-probe transmission measurements are used to isolate instantaneous nonlinearities from cumulative processes. These techniques, together with a simple rate equation model, have allowed us to extract information regarding mid-gap levels and to measure both the two-photon absorption coefficients and the free carrier absorption cross sections in these samples. Our model, together with Z-scan and beam deflection measurements of the nonlinear refraction, has provided the change in index due to each photogenerated electron-hole pair.

Two schemes for sub-nanosecond bistable switching using nonlinear waveguiding in coupled semiconductor lasers are described and analyzed. Using longitudinally coupled lasers in an external cavity gives rise to photon lifetime limited switching, but the system is cumbersome and susceptible to low-frequency self-pulsations and noise. Laterally coupled twin stripe lasers offer a monolithically integrated alternative, in which switching times are limited by carrier diffusion.

The large third order susceptibility of Hg1_CdTe makes it a very promising material for many applications, including optical switching. There have been numerous studies' 4) ofthe optical nonlinearities of Hg1_CdTe and it is well known that for values ofx near 0.2 and for 10.6 ,tm radiation, both nonlinear absorption arising from two photon absorption and nonlinear refraction arising from the charge carriers generated by two photon absorption play a role in determining the overall nonlinearity. To optimize the performance of a device that utilizes the nonlinearity of Hg1 _CdTe it is sometimes necessary to separate the relative contributions of these two mechanisms. The recently developed "z-scan" technique provides a convenient way of achieving this5. We present here a study of the nonlinearity of Hg1_Cd7Te using the z-scan method. In the next section, we first describe a theory of z-scan results expected for the external self focusing case. Although there are many theoretical studies67 of the external seLf focusing case, it is hard to find them presented in a general form from which many cases of interest can be easily evaluated. Moreover, the refractive nonlinearity is usually assumed to be of the Kerr-type, which is not in general true. Also, the effects of nonlinear refraction and absorption are usually not considered together. We present our results here in terms of dimensionless parameters, and inclilde the near field and far-field effects. We also take into account the time dependences of the incident laser beam and the nonlinearity of the medium. The results are presented in forms of integrals which can be evaluated for arbitrary nonlinear phase changes. Next, we apply the theory to the case of Hg1 _Cd1Te in which the dominant nonlinear phase change arises from refraction due to generated free carriers and the dominant nonlinear absorption arises from two-photon absorption. The generation of the charge carriers via two-photon absorption and their decay by means of Auger recombination are taken into account. The temporal profile of the laser beam used in the experiment described in section 3 was close to Gaussian-this was taken into account in the theory.

Abstract not available.

We present measurements of nonlinear absorption and refraction in semiconductors used in the realization of optical limiters. We show that nonlinear refraction at 532 nm in ZnSe is caused by a negative third order electronic Kerr effect in addition to the two-photon-absorption (2PA) induced carrier refraction. We have used time-resolved beam distortion, picosecond time-resolved degenerate four-wave mixing and our recently developed Z-scan technique to determine the sign and magnitude of the 2PA coefficient, the bound electronic nonlinearity, n2 and the refractive index change per free carrier.

We have used a physically realistic model to investigate the spatial and temporal behavior of reverse saturable absorption and optical limiting in organometallic cluster compounds. An algorithm was developed to solve numerically the model and is used for the case of a collimated beam to determine various material parameters by fitting theory to experimental optical limiting data. Using these parameters, the algorithm was then extended to the case of converging and/or diverging beams.

Ground and excited state absorption spectra along with optical limiting measurements have been made on a series of systematically altered organometallic cluster compounds. Measurements using 8 ns pulses at 532 nm on methylene chloride solutions of iron-tricobalt organometallic cluster complexes (70% nominal transmission) show limiting throughputs of 350-700 mJ/cm2 without focusing. The optical limiting properties are shown to be minimally dependent on counter-ion substitution indicating little perturbation in the cluster bonding. Optical limiting is shown to be strongly dependent on ligand substitution. Ground state and excited state absorption spectra reveal broad features indicating the materials can be used as limiters over a large spectral range (>lOOnm) . Temporal pulse narrowing of 8 ns pulses to 5 ns at 532 nm was observed, indicating subnanosecond intersystem crossing. The lifetime of the excited state was determined to be 115 ns, much longer than the pulse length, indicating that efficient limiting occurs for longer pulses. Optimization of optical limiting properties is discussed.

Laser-induced grating spectroscopy on the picosecond tinie scale was used to characterize the nonlinear optical properties of CdTe and KNbO which have potential applications for optical limiting. The magnitudes and response times of nonlinear optical signals were measured and the results were used to understand the nature of the fundamental physical effects responsible for the nonlinear responses. Experiments were performed to demonstrate optical limiting through two-beam coupling, polarization rotation, and four-wave mixing.

We present the results of a detailed study of the optical nonlinearities of liquid crystals spanning the picosecond-millisecond time scale. These nonlinearities are utilized in some optical limiting/switching applications with infrared and also visible lasers.

We have characterized the nonlinear optical properties of carbon black particles in liquids and layers deposited on glass. We find that the limiting is dependent on the energy density (fluence) and that the material changes from a linear absorber to a nonlinear scatterer for fluence levels 0.2 J/cm2 and 0.38 J/cm2 for 0.532 jim, 14 ns and 1.064 pm, 20 ns laser pulses respectively. In this paper, we will discuss the possible mechanisms that have been proposed to explain the nonlinear scattering. These mechanisms are plasma formation, micro-bubble formation and change in index of refraction of the liquid surrounding the particles. We will show through a series of experiments that plasma formation is consistent with all of the experimental results while bubble formation may influence the limiting behavior at fluence levels substantially above the limiting threshold. In this model, the microscopic carbon particles are heated by linear absorption to a temperature at which a plasma can be created by the optical field. These microplasmas rapidly expand, thus scattering the incident light and limiting the transmittance.

Thermal defocusing, nonlinear scattering and deflection, and nonlinear quarter-wave stack switches are passive limiters that have the ability to be extremely fast, simple in design, and require little maintenance. In this paper we model the performance of these devices in terms of transmission and/or throughput energy. A simple optical design is considered in which incident radiation from infinity is focused on the device, then recollected and reimaged on a detector plane. Values for the effective nonlinear index of refraction and the nonlinear time response are chosen which limit the incident radiation to a specified optical density. The overall performance of the protection device can then be investigated based on the dynamic range, damage threshold, and linear transmission.

Nonlinear refractive index and two-photon absorption measurements on semiconductors show that the bound electronic nonlinearity can be calculated from two-photon absorption dispersion via a simple Kramers- Kronig analysis. This analysis shows n2 changing from positive to negative as the photon energy approaches the band-gap energy, consistent with observations. Additionally, this simple calculation, which assumes two parabolic bands, gives good agreement with measured values of n2 in wide-gap dielectrics that are 2 to 3 orders of magnitude smaller than in semiconductors.

We investigate a model of a simple, passive optical device intended to limit the transmitted power of a laser beam by utilising self-focusing or self-defocusing. In such a device a broad distinction can be drawn between external self-focusing, which may be accomplished with thin nonlinearly-refracting media, and internal self-focusing, which requires suitably thick media. Analytical requirements for satisfactory limiting behaviour have been obtained for a two-lens device configuration, involving the various parameters for the incoming light, the thin active medium, and the optical components. Series expressions have been derived for both the transmitted intensity and the optical power transmitted by an aperture stop, symmetrically placed at an arbitrary position beyond the imaging lens, where the incident beam is gaussian-shaped. The application of the model to the measurement of nonlinear indices is discussed. A new z-scan technique for measuring n2 has been devised, and is shown to provide a three-fold enhancement in sensitivity compared with existing methods.

An attempt is made to study the heat capacity in 1uantum dots ( QDs) of nonlinear optical materials, taking n-LdGeAs2 as an example which also finds extensive applications in light emitting diodes. have for rnul ate d the he at c apac i ty in the QDs o f the s al d mater Ial by deducing a new dispersion law, within the framework of k.p. formalism Considering all types of anisotropies in the energy para- ieters. It is found, that the heat capacity increases with increa sing carrier density and decreases with increasing film thickness in an oscillatory manna' for both the eases respectively. The well known special eases have been derived from our generalized formula- tions under certain special conditions. The theoretical ex'essions are in agreement with the experimental observations as reported elsewhere.

Data on advances in the technology of a new patented infrared source are presented. Infrared output from 3 to 12 microns is produced by the modulation of the emissivity of silicon. Information on the long term stability and on various applications for the source is provided.

This paper briefly reviews current methods intended to test automatic target recognition systems (ATRS) and the databases needed to support these methods. A new approach to field testing ofATRS is described.1 This approach can also provide means ofgenerating needed realistic, closely documented imagery for ATRS development and testing.

A directional-directional reflectance accessory based on a parabolic mirror has been designed for convenient use with a Fourier Transform Infrared (FTIR) spectrometer. As compared to directional measuring devices based on lasers, the system offers the advantage of measuring continuously over a wide wavelength region. A simple anisotropically reflective sample was utilized to demonstrate the system capabilities. In addition, candidates for diffuse reflectance standards were evaluated.

Polarimetiy and spectropolarimetry are optical measurement techniques which use polarized light to obtain electrooptical material property information. These techniques are being used to make measurements on infrared electrooptical materials. Infrared materials of interest are those which find use in two dimensional modulators, i.e. optical picessing applications and infrared scene projectors. Polarimetry measurements are made at one infrared wavelength at a time using laser sources. Spectropolarimetry measurements are made over an entire infrared spectral region, e.g. 2 to 14 tm. A Fourier transform infrared spectrometer is the source of radiation in this case. The Mueller matrix formulation can be used to describe the polarized light and its interaction with the sample and measurement system optics. A Mueller matrix of the sample can then be obtained from a series of measurements with different input polarization states. The sample Mueller matrix contains information on the polarization properties. Electric fields are imposed on the sample as optical measurements are made. Fundamental constants associated with the sample material can be derived from the measured Mueller matrix elements.

In general, transmissive optics introduce aberrations into transmitted wavefronts whenever temperature gradients exist within or across the optic. The aberrations result from thermally induced optical path length (OPL) changes, and materials that minimize the effect are often labeled as "athermal". Several groups of materials which appear to meet the criteria for "athermal" behavior are glasses pssessing highly negative thermo-optic coefficients (dn/dT). Heavy metal fluoride (HMF), phosphate (PP), fluoro-zirco-aluminate (FZA), and fluorophosphate (FP) glasses exhibit this somewhat unusual property. A program to investigate HMFGs, PPs, FZAs, FPs and other temperature insensitive materials has been underway at the USAF Weapons Laboratory since May of 1988. Of particular interest is the effect of glass composition Ofl the refractive index, index temperature dependence, thermal expansion coefficient, and heat capacity. Analyses have shown that the materials under investigation are highly superior to fused silica from a thermally induced optical distortion standpoint. The WL program has produced a wide variety of glass samples that are now undergoing optical, thermal, and mechanical evaluation. This paper discusses the analyses thus far accomplished.

The infrared absorption in thin film polycrystalline diamond deposited in a microwave plasma is examined using Fourier transform infrared spectroscopy (FF-IR). The incorporation of small amounts of hydrogen during the growth process resuits in absorption in the "C-H stretch" region at 3.5 pm and 3.42 jim as well as absorption in the extrinsic defect related single-phonon region from 7jim to 12 rim. This absorption is precisely in the 8 jim to 12 jtm band where high transmittance is required by long wave infrared optical systems and therefore the amount of hydrogen incorporated during vapor phase growth of diamond could limit this materials usefulness as a bulk optical material. The effects of growth conditions and high temperature annealing on the absorption in these two IR regions are discussed. IR spectra are compared with Raman spectra and hydrogen content measured by nuclear reaction analysis.

Chemically vapor-deposited ZnSe exhibits outstanding properties in the infrared (IR) and has been established as a prime material candidate for IR transmitting applications. The purpose of this paper is to present and evaluate data on both the surface and the bulk absorption of commercially available ZnSe, over the entire wavelength and temperature range of current interest. This investigation is based on spectral emittance measurements that were carried out by Stierwalt at the Naval Ocean Systems Center and on in-house transmission spectroscopy performed in the context of a fur-window development program. Surface effects can be felt at wavelengths as high as 14 um and usually predominate at wavelengths of less than 8 urn, even for fairly thick specimens. Fractional surface absorptions are temperature independent from about 200 to 400 K, which masks the behavior of the bulk absorption, and can be fitted to a Fourier series, for wavelengths of 3.5 to 13.5 urn. Bulk absorption coefficients (nv) are strongly dependent upon temperature as well as wavelength but can be approximated by means of two bivariate polynomial expressions that yield "recommended" values. At wavelengths X 10 urn, v always decreases with increasing temperature; it is shown that a wavelength independent Debye-Waller factor provides a correct description of the temperature dependence, thus pointing to IR-active localized modes. At wavelengths X 14 urn, V always increases with rising temperature and exhibits a temperature-dependence pattern as predicted for 3- and 4-phonon summation processes. Finally, an analysis of the temperature dependence of j at 10.6 urn demonstrates that the intrinsic lattice-vibrational contribution to bulk absorption at the CO2-laser wavelength should be close to 4x1Ocrn, in accord with the results of earlier lasercalorimetry tests performed on exceptionally pure ZnSe.

Cadmium telluride is the primary choice for electro-optic modulator applications in the mid infrared region - particularly at 10.6 micron. In principle, single crystal CdTe in the rest state is only weakly birefringent along the {1 1O} planes. Some internal birefringence does exist, however, due to fabricated-in stress birefringence and birefringence associated with slippage of the crystal along the {1 1 1} planes. When a voltage is applied to a CdTe crystal, the total phase shift introduced by the crystal is a result of the combination of the electro-optic effect and the residual birefringence. This paper will present a method of measuring the phase shift produced by residual birefringence in CdTe modulators at 10.6 micron. The test method is a modification of the crossed polarizer technique. Test results will be presented for CdTe modulators with voltage and without voltage.

The precise (five number) infrared refractive index of AMTIR-I glass and chemical vapor deposited zinc selenide were measured over the wavelength range 3-l2pm. The results were temperature corrected and compared to standard values.

Modifying the emissivity of non-planar surfaces and objects with complex geometries has proven to be a difficult task. Optical interference coatings have been successfully used to change the spectral emissivity of a surface. However, typical deposition processes for these coatings, such as evaporation, are line-of-sight processes that require complex masking and/or rotation systems in order to coat non-planar surfaces. Objects with very complex geometries cannot be coated at all by line-of-sight processes. In addition, evaporative processes often do not provide films with good resistance to thermal cycling to high temperatures. Low Pressure Chemical Vapor Deposition (LPCVD) is a non-line-of-sight process that unifonnly coats all exposed surfaces of objects with complex shapes. DSI has developed an LPCVD process that is capable of the routine manufacture of optical interference coatings. We have used this process to deposit high quality, uniform, conformal coatings for the modification of the emissivity of a variety of materials including ceramics and metals. Coatings of these substrates in very complex, non-planar forms have been demonstrated. The coatings show excellent durability and withstand repeated cycling to high temperatures. In this paper we will briefly describe the coating process, show examples of some of the substrate forms, and describe the spectral and environmental performance of these emittance control coatings.

New method of high speed temporal modulation of infra-red. wave beams, reflected from thin films of semiconductor's plasma with free carriers, is proposed. The physical foundations of such method, based on non-linear properties of free carriers plasma in these films, show the possibilities of elaboration of high-speed tunable modulators and polarizers. The reflection of continuous wave beam from the film with tunable reflection coefficient leads to pulses shaping, the pulse duration being as small as 1 nsec. The electric power, necessary for tuning of such modulator, is as small as (formula in PDF)

The annealing behavior of Hg1CdTe layers, grown by the conventional Organometallic Vapor Phase Epitaxy (OMVPE) , is reported. As grown layers, which are p-type with a concentration around 4 x 10'6/cm3 of mercury vacancies, become light p-type with carrier concentrations around 1-2x 10'5/cm3 after Hg saturated annealings at temperatures in the range of 200-230°C. These conditions, usually sufficient for the complete annealing of bulk Hg1_CdTe, to n-type, are thus inadequate for OMVPE grown epilayers. The as grown layers are converted to n-type with a carrier concentration of approximately 5 x 10'4/cm3 by a higher temperature anneal at 290°C, followed by a low temperature anneal at 220°C. Hall effect measurements were made under variable temperature as well as variable magnetic field conditions. Bulk carrier concentrations and mobilities were evaluated by considering the effect of the surface inversion/accumulation layer on the Hall data. It is proposed that ptype conduction in the partially annealed layers is due to the persistence of vacancies in the Hg1_CdTe layer, which are not completely annihilated during the low temperature anneal. Conversion to n-type is probably due to residual donor impurities in the as grown Hg1_CdTe layer.

HgCdTe epitaxial layers were grown on (111)B CdTe substrates in a commercially purchased and modified vertical MOCVD reactor. DIPTe, DMCd and elemental Hg were used as reactants and growth takes place at 360°C. Run-to-run reproducibility of composition and electrical properties was studied over a hundred growth runs. Hall measurements show that n-type material is consistently obtained with carrier concentrations in the mid 10'4/cm3 and mobilities as high as good bulk material. LWIR photoconductive devices were fabricated with this low carrier concentration material and tested. The responsivity and the lifetime measurements indicated that these devices perform as well as those fabricated with purchased LPE material. Excellent device performance was obtained on 80-element photodiode arrays fabricated with x''0.3 p-type HgCdTe samples by formin9 flf/p junctions by ion implantation. R0A values obtained are ..1x1Ob Q-cm2 at 77K for Xco 5.7 1m and are highly uniform within an 80-element array. We also report on an all MOCVD grown p-on-n double-layer heterojunction (DLHJ) photodiode with Xco 8.1 um.

Mercury cadmium telluride has successfully been grown from tellurium rich solutions. Solution growth offers a number of advantages over other thin film and bulk growth techniques, e.g. purification, thin film and bulk growth, low dislocation density, and inexpensive growth equipment. The principal solution growth techniques that have received the most attention for (Hg,Cd)Te so far have been liquid phase epitaxy(LPE), the traveling heater method(THM) and the solid state recrystallization(SSR) process. These techniques have provided very high quality material for various device structures. The solid state recrystallization process, the traveling heater method and liquid phase epitaxy are reviewed and their similarities described.

The effect of photochemical deposition of Si02 on the currentvoltage characteristics of the InSb pn diodes was studied. By applying different voltages on the gate electrode over the pn junction periphery, various kinds of current-voltage characteristics can be induced, including multiple negative differential resistance in forward bias. This strongly indicates that the major part of the current, especially the reverse leakage current, flows through the surface of the p+n junction. Reverse leakage current as low as 20 A/cm2 at -1.1 V for a p+n diode with n-type doping concentration of 2 x i0 cm3 could be easily achieved by applying a gate voltage of -9 V. It is also found that diodes with similar performance can be fabricated by properly adjusting the photochemical vapor deposition passivation process.

In this paper, an attempt is made for the first time to study the Einstein relstion for the diffusivity-mobility ratio of the elec' ons in mercury cadmium teliuride from the consideration of the fourth order in the effective mass theory and taking into account the interactions of the conduction, heavy-hole, light-hole and split-off bands respectively. The D increases with increasing electron concentration and decreasing film thickness in an osdilla- tory manner. The results are in cjuantitative aeement with the suggested experimental method of determining the Einstein relation in degenerate compounds having arbitrary dispersion laws. The results in accordance with various other models have also been derived for the purpose of comparison. The well-known results for relatively wide gap materials have been obtained as special cases under different limiting conditions of our generalized formalism.

Narrow-band-pass (NBP) interference filters are commonly used in the infrared (IR) spectral region. It may happen that such a filter is to be used in conjunction with an optical system which must pass thermal radiation in the 8 to 12 m wavelength range. Thus the NBP filter must be designed in such a way that it also transmits from 8 to 12 pm. This paper presents two design techniques for achieving the required performance. In one technique two reflective stacks are used, providing blocking on either side of the NBP region. Additional layers are used to provide the transparency over the region 8 to 12 m. The second approach involves using a multiple-cavity Fabry-Perot filter to achieve the NBP performance. The long-wave--pass region can be achieved by varying the refractive index of selected layers within the multilayer coating. Changing these indices has a minimal effect on the performance in the pass band. The above design techniques are applied to the NBP filter with the following specifications: Pass-band center: 4.0 m Pass-band width: m Pass-band transmittance: 80% Pass-band edge slope: ( 0.05 im (5% to 95%) Long-wave region: 8-12 m Long-wave transmission: T 90% One useful design trick that can be employed takes advantage of the fact that the long-wave transmission region covers a range of wavelengths which are approximately twice the wavelength of the NBP region. Thus layers with a halfwave optical thickness of 4 pm can be added without affecting the NBP performance. These layers will have an optical thickness close to a quarterwave over the 8 to 12 pm range and can be used to reduce the reflectance over this region.

Liquid crystals consist of anisotropic organic molecules which are orientationally ordered in the nematic phase. The birefringence of these materials gives a measire of the degree of orientational order. In addition to the linear birefringence, liquid crystals possess large third order nonlinear susceptibilities. Due to the bulk anisotropy of these materials, the nonlinear refractive index 2 depends on the direction of polarization of light with respect to the nematic director. We have used the Z-scan technique' to determine the third-order nonlinear refractive indices n2 and nonlinear absorption coefficients j3 of the pure liquid crystal 5CB (4-cyano-4'--npentylbiphenyl) in both the nematic and the isotropic phases. We have measured the nonlinear refractive indices n211 and n21 for light polarized parallel and perpendicular to the director, using both a CW Ar laser and a nanosecond frequecy-.doubled Nd:YAG laser. The nonlinear index n2 of 5CB in its nematic phase, measured with 7ns Nd:YAG laser pulses, is more than two orders of magnitude larger than that of CS2, and originates in a self-defocusing process. We have also observed strong nonlinear birefringence, the divergence of the nonlinear refractive indices as the nematic-isotropic transition is approached from below, and strong polarization dependent nonlinear absorption.