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We report a single-beam, differential z-scan technique with improved sensitivity for the determination of nonlinear absorption and refraction of materials. A sample is scanned in the direction of beam propagation as usual, but, in addition, its longitudinal position is dithered, producing a detector signal proportional to the spatial derivative of only the nonlinear transmission and therefore giving a background-free signal; the nonlinear transmission for any spatial position of the sample can be recovered by simple integration. For both open and closed aperture scans in GaP, we find an improvement in the signal-to-noise ratio of >5x compared with a balanced z-scan setup, but this can be improved with apparatus optimization. Nonlinear phase distortions OCIS codes: 190.0190, 190.4720.

Spherical retroreflectors have a much greater acceptance angle than conventional retroreflectors such as corner cubes. However, the optical performance of known spherical reflectors is limited by spherical aberration. It is shown that third-order spherical aberration may be corrected by using two or more layers of homogeneous optical media of different refractive indices. The performance of the retroreflector is characterized by the scattering (or radar) cross section, which is calculated by using optical design software. A practical spherical reflector is described that offers a significant increase in optical performance over existing devices. No gradient index components are required, and the device is constructed by using conventional optical materials and fabrication techniques. The experimental results confirm that the device operates correctly at the design wavelength of 690 nm. OCIS codes: 230.1150, 220.3620, 120.4640.

I report on the measurement of threshold energy fluence for optical limiting of nanosecond and microsecond pulses in a high-performance carbon suspension known as Defence Research Establishment Valcartier carbon black suspension (CBS)-100. Thresholds as low as 24-mJ/[cm.sup.2] (nanosecond regime) and 100-mJ/[cm.sup.2] (microsecond regime) have been obtained. The measurement technique, based on an f/20 optical system and a small analysis aperture, has been tested by measurement of reverse saturable absorber materials and other carbon suspensions whose properties can be found in the technical literature. A factor of merit has emerged from these measurements that could be used to order by limiting performance the different types of carbon suspension. In this ordering, CBS-100 appears as the best choice in the set of suspensions tested for short and long pulses. OCIS codes: 160.4330, 230.4320, 160.4670, 190.4400, 140.3360.

On the basis of calculations under the discrete dipole approximation and a proposed extended model of nested ellipsoids for bipolar droplets, the changes in optical properties of a spherical liquid-crystal droplet, caused by a change in director configuration under the influence of an external field, have been considered. OCIS codes: 160.0160, 160.3710, 290.2200.

A novel method used in the production of compositional gradients in homogenous monomer-monomer, polymer-polymer and monomer-polymer mixtures was studied by use of centrifugal fields. It was shown that compositional gradients cannot be produced in monomer-monomer and polymer-polymer mixtures under the experimental conditions investigated. Results showed that these materials and processes are potentially useful for producing optical components such as self-focusing lenses.

A mathematical model is presented to characterize the performance of a lanthanum-modified lead zirconate titanate electro-optical cylindrical structure with an arbitrary number N of lateral electrodes switched with a series of voltages [V.sub.0] and [V.sub.0] + [Delta]V. The method yields a solution that can be written as a sum of numerical and analytical components, and the contribution of numerical components becomes increasingly smaller as the electrode wrapping angle is decreasing below [Pi]/3N. The effects of the electrode wrapping angle and the switching voltages on the induced refractive-index distribution and electrode capacitance are analyzed. It is shown that the design offers a simple and compact structure that performs dynamic light diverging with a focal length that can be controlled by the applied voltage. The possibility of light steering is considered for a two-electrode structure.

We present novel, to our knowledge, methods for the analytical design and recording of planar holographic optical elements in thick materials. The recording of each planar holographic element is done by interference of two aspherical waves that are derived from appropriately designed computer-generated holograms such that the element has the desired grating function for minimizing aberrations and closely fulfills the Bragg condition over its entire area. The design and recording methods are described, along with calculated results of representative elements. OCIS codes: 090.2890, 090.1760, 090.2900.

Tracing of a random profile with a mechanical profiler with a spherical tipped stylus has been investigated by means of computer simulation. It is shown that the fractional measuring errors of rms roughness depend on only the ratio of rms roughness [Sigma] to the stylus tip radius r and the ratio of rms roughness to the 1/e correlation length [[Rho].sub.c]. The ratios [Sigma]/r were in the range of 0.005-0.05 and the ratios [Sigma]/[[Rho].sub.c] were equal to 0.028 and 0.048. Key words: Stylus tip, rough surface, rms roughness, surface profile.

Continuous-wave ultrasonic modulation of scattered laser light was used to image objects buried in tissue-simulating turbid media. The buried object had an absorption coefficient greater than the background turbid medium. The ultrasonic wave that was focused into the turbid media modulated the laser light that passed through the ultrasonic field. The modulated laser light that was collected by a photomultiplier tube reflected the local mechanical and optical properties in the zone of ultrasonic modulation. Objects buried in the middle plane of 5-cm-thick dense turbid media were imaged with millimeter resolution through the scanning and detecting alterations of the ultrasound-modulated optical signal. The optical properties of the dense turbid media included an absorption coefficient of 0.1 [cm.sup.-1] and a reduced scattering coefficient of 10 [cm.sup.-1] and were comparable with those of biological tissues in the visible and near-IR ranges. The dependence of the ultrasound-modulated optical signal on the off-axis distance of the detector from the optic axis and the area of the detector was studied as well. Key words: Ultrasonic modulation, acousto-optics, optical imaging, optical tomography, turbid media.

We describe a novel approach to refractive-index reconstruction in two-dimensional systems with no special symmetry, based on observation of traces of rays that travel through the optical system. The mathematical model of ray-tracing analysis is presented in detail, and both the analytical and numerical solutions are given. Methods of data processing in the presence of experimental errors are developed and applied to model problems. Key words: Refractive-index distribution, ray-tracing, gradient-index lens, nondestructive diagnostics.

Antireflection filters based on multilayer stacks of dielectric and polysilicon films on monocrystalline silicon combined with charge collection in different (poly)Si layers can be used to realize sensors with a programmable spectral response controlled by weighted summing of the photocurrents detected in the polysilicon and the substrate. Thus, employing both interference and selective absorption of light yields increased photoelectric efficiency and improved flexibility of spectral control and enables on-chip integration of the detector(s) with the signal conditioning and processing circuits. The potential of thin-film color sensors has been evaluated for this purpose. However, for practical implementation of such structures the problems associated with the realization of reliable photodetectors in polysilicon must also be considered. Phosphorus passivation of the grain-boundary states has been employed to yield polysilicon photodiodes with improved electrical characteristics and reliable light and color detection. We present the design methods of thin-film color sensors employing silicon-compatible materials only. The measurement results of a fabricated structure fully demonstrate that such sensors can be realized with good spectral selectivity. Key words: Interference filter, thin films, color sensor, polysilicon photodiodes, silicon-compatible materials.

The optical performance of photodetectors in silicon strongly depends on the transmission of incident light into Si and the charge collection efficiency therein. Consequently, improving the transmission efficiency of light into Si by means of an interference antireflectant (AR) filter can lead to improved optoelectric conversion efficiency. However, the design of these filters requires the availability of data on the optical characteristics of the materials used. Furthermore, for the realization of such filters for light detectors realized in silicon, the required compatibility with standard microelectronic processing implies that only Si-compatible materials should be used. The range of such Si-compatible materials available for fabricating photoelectric devices in silicon includes thermally grown Si[O.sub.2], low-pressure chemical-vapor deposited polysilicon, silicon nitride (low stress and stoichiometric), and oxides (low-temperature oxide, phosphosilicate glass, borosilicate glass, borophosphosilicate glass) as well as plasma-enhanced chemical-vapor deposited oxynitrides. We present the refractive index and the extinction coefficient of these materials in the 380-800-nm range. The data presented enhance the accuracy and applicability of simulation and design tools used to design photodetectors in silicon for the visible range. Key words: Interference filter, thin films, silicon-compatible materials, color sensor.

A systematic analysis has been performed that predicts the existence of 36 cases in which 100% modulated, square-wave irradiance distributions can be generated in the Fresnel regime by simple binary-phase gratings. These types of distributions, referred to here as Lohmann images, have been previously predicted by researchers studying phase gratings known as Talbot array illuminators. Twenty of the cases are reported, to the best of my knowledge, for the first time. Sixteen of these new cases result in Lohmann images with twice the spatial frequency of the original grating. Experimental verifications of the theoretical predictions are presented. Key words: Talbot effect, array illuminators, optical interconnects, Fresnel diffraction, binary optics.

Highly polarization-selective diffractive optical elements for use in optical interconnection and routing systems have been fabricated by the wet etching of pairs of calcite substrates and characterized experimentally. We show that when an index-matching polymer is used to fill the gap between the two substrates, substrate alignment problems are eliminated and efficiency is greatly increased. This has resulted in first-order diffraction efficiencies of 40.5% and polarization contrast ratios of 450:1 for several off-axis binary-phase elements, allowing these components to be used for practical applications. Key words: Diffractive optical elements, birefringence, index-matching polymers, optical interconnects.

In general, as diffractive optical elements formed by use of self-repeating patterns possess beneficial characteristics such as scratch resistance, low design effort, ease of fabrication, and natural formation of large panels, an efficient design methodology that was developed with a modified preserving-the-best strategy of genetic algorithms is presented. Both genetic algorithms and simulated annealing are examined by the Markov-chain stochastic process to create the insight needed to use these two heuristic algorithms efficiently. It was found that adding the preserving-the-best strategy to traditional genetic algorithms guarantees the possibility of locating the global optimum. Combining this sufficient and necessary condition for locating a global optimum for genetic algorithms with the built-in chromosome crossover searching mechanism and its neighborhood identification makes this newly developed genetic algorithm an effective method for designing diffractive optical elements. In our study, a prototype was fabricated based on our case study with the modified genetic algorithm. The performance of this prototype was measured and analyzed. Experimental results are shown to agree well with theoretical predictions. Key words: Diffractive optical elements, binary optics, genetic algorithms.

Diffractive optical elements with blazed profiles can, in theory, have 100% relative efficiency. We review several methods for making such elements and compare their advantages and limitations. Our emphasis is on processes to produce elements other than those with approximate, stepped surfaces, such as binary optical elements. For optical methods, we offer an expression relating the maximum numerical aperture of a diffractive lens with a given maximum efficiency to the numerical aperture of the recording system. Key words: Diffractive optics, optical fabrication methods.

Binary optics are an important part of modern optics, but they have some inherent problems because of their binary nature. The optics cannot achieve maximum efficiency unless the rms surface error can be reduced. A technique for smoothing jagged surfaces by use of isotropic etching is presented. We show that etching smoothes the binary nature and improves the optical efficiency. Key words: Binary optic smoothing, isotropic etching, surface modification.

The composition-dependent structural, microstructural, optical, and mechanical properties of Ti[O.sub.2]-Mg[F.sub.2] composite films prepared by reactive electron-beam coevaporation at a substrate temperature of 280 [degrees] C are systematically investigated with an x-ray diffractometer, transmission electron microscope, spectro-photometer and varied angle of incidence spectroscopic ellipsometry, and microhardness tester, respectively. A comparison of the films prepared by reactive ion-assisted coevaporation shows that the films prepared by reactive electron-beam coevaporation have lower refractive indices and hardnesses. However, Ti[O.sub.2]-Mg[F.sub.2] composite films prepared by both techniques exhibit similar softening and hardening phenomena and similar microstructures. Key words: Microstructure, optical properties, hardness, composite films, reactive electron-beam coevaporation, reactive ion-assisted coevaporation.

A new interferometric method for measuring the refractive-index distribution in a plane-parallel section cut from a gradient-index lens blank is described. A standard double-pass interferometric scheme modified to provide a single pass of the beam through the investigated gradient-index sample is used. The two-dimensional variation of the refractive index in dimensions transverse to the sample surface is measured with an accuracy of better than 1 x [10.sup.-4]. Key words: Gradient index, optical testing, interferometry, nondestructive testing, refractometry, optical properties, index of refraction.

A low-cost add-on to commercial Fourier-transform spectrometers that have a continuously scanning Michelson interferometer has been developed for high-resolution, broadband, time-resolved spectroscopy. A number of innovations have been implemented to enable near-IR, visible, and UV photoluminescence studies. These include error correction and normalization of interferogram points to correct for laser intensity variations and missed shots, reduction of mirror-speed variations with recognition and avoidance of the timing mistakes they cause, and simple white-light-interferogram advancement optics that leave high-frequency modulation efficiency for the signal of interest unchanged in dynamically aligned systems. Application to energy-transfer phenomena in solid-state-laser media is described. Key words: Time resolved, Fourier, spectroscopy, laser crystals.

The air gap between an attenuated-total-reflection (ATR) element (prism) and a sample surface reduces the intensity of each recorded spectrum from that sample and distorts the IR-band contours. Recently, the air-gap problem was solved with a moldable ATR element made of IR-transparent chalcogenide glass. When heated to the softening temperature (60-90 [degrees] C) and then cooled to room temperature together with a pressed specimen, such an element provides perfect contact with the surface of a rough sample. Some advantages of this new technique are demonstrated. Key words: Attenuated total reflection, optical material.

The reflectivity and transmission of a multiple-layer substrate are simulated to predict the optimum choice of materials for the fabrication of phase-shifting masks for optical lithography. Two types of materials are described: a transparent shifter layer with a refractive index closely matching that of quartz, and a partially transparent layer (5-15% transmission) inducing a 180 [degrees] phase shift of light compared with air. A possible refractive index n and extinction coefficient k are defined, for both layers of the partially transparent material. The fabrication tolerances are calculated in terms of refractive index, extinction coefficient, and thickness accuracy. One of the major technological challenges for both material types is to control the thickness to [+ or -]2%, which is required to satisfy the phase-shifting mask specifications for deep UV lithography ([+ or -]0.5% transmission control and [+ or -]4 [degrees] phase control). These criteria were calculated by the simulation of the phase and transmission errors, thereby inducing a [+ or -]10% linewidth variation of the resist patterns on the wafers.

The excitation of surface plasmons at a dielectric-metal interface is responsible for dips in the zeroth order diffraction efficiency of a metal grating at certain angles of incidence. The dips appear as dark bands in the returning irradiance pattern in an optical disk system and are seen only when there is a component of incident polarization that lies perpendicular to the tracks. The location of these bands is derived from theoretical considerations and is shown to depend on the track pitch and the materials involved, but not on the groove depth or width. The band locations are confirmed by zeroth order diffraction efficiency measurements as a function of incident angle. A possible negative effect of these bands on an optical disk system is the introduction of additional fluctuations and noise into the focusing and push-pull tracking signals.

We have developed an instrument for directly measuring the emissivity of reflective surfaces at near-millimeter wavelengths. The thermal emission of a test sample is compared with that of a reference surface, allowing the emissivity of the sample to be determined without heating. The emissivity of the reference surface is determined by one's heating the reference surface and measuring the increase in emission. The instrument has an absolute accuracy of [Delta]e = 5 X [10.sup.-4] and can reproducibly measure a difference in emissivity as small as [Delta]e = [10.sup.-4] between fiat reflective samples. We have used the instrument to measure the emissivity of metal films evaporated on glass and carbon fiber-reinforced plastic composite surfaces. We measure an emissivity of(2.15 [+ or -] 0.4) X [10.sup.-3] for gold evaporated on glass and (2.65 [+ or -] 0.5) X [10.sup.-3] for aluminum evaporated on carbon fiber-reinforced plastic composite. Key words: Emissivity, reflectance, millimeter, infrared, mirrors.

A method for fabricating refractive micro-optical elements by structuring poly(methyl methacrylate) layers is presented. With this flexible and simple method a surface growth of several micrometers can be achieved. For smooth surface reliefs a nearly linear response of the phase growth to the UV intensity can be achieved over a range of 8[Pi]. The edge steepness depends on the maximum height and can reach values as high as 2[Pi] above 4 [[micro]meter]. We describe the fabrication process, establish a mathematical model of the surface growth, and also present as experimental results some components fabricated by this method. Key words: Computer-generated holograms, phase-only filters, fan-out elements, optical materials, polymers, microlenses.

Surface plasmons generated at a silver-polyimide interface and the guided modes coupled into planar films cause dips in the reflectivity curve of a transparent dielectric-silver-polyimide-air structure. These minima in the reflectivity curve were used to measure the polyimide thickness as well as the real and imaginary parts of the polymer refractive index (extinction). Precision within 1% of the polymer coat thickness was achieved through the use of this technique over the range 0.5-10 [[micro]meter]. In some cases, this technique is capable of yielding a precision of [approximately] 10% on the imaginary part of the polymer refractive index and provides a useful method for determining the performance of a low-loss polymer waveguide. Techniques in fitting the experimental reflectivity data to obtain the optical constants are also described.

Analytical expressions for the Fourier coefficients are presented that permit the effects of source polarization to be included in the analysis of ellipsometric data for the inference of the optical properties of bulk samples. The developed expressions are general and can be obtained for any ellipsometer system as long as the source-optics characteristics are known. In addition, no constraints are imposed on the angle of incidence of the light beam and on the polarizer/analyzer azimuthal angles. We obtained measurements on an amorphous carbon sample at a temperature of 25 [degrees] C and in the 400-700-nm wavelength range and analyzed the data using the discrete Fourier transform. Comparisons were carried out for the inferred refractive indices with and without the source-polarization effects. We show that for the source optics and sample used in this study the real part of the index increases by 1.5% when the source-optics parameters are included, whereas the imaginary part of the index decreases by as much as 12%. Thus the correction should not be neglected when accurate values for the indices are to be obtained from the complex ellipsometric parameters of the sample surface.

A sphere lens with a spherical gradient index (GRIN) was prepared by the modified suspension polymerization technique. GRIN spheres with quadratic- and linear-index distributions were obtained by two different methods to confirm the effect of the GRIN profile on the focusing property of the sphere lens. It was confirmed in both theory and experiment that the spherical aberration of such GRIN spheres was remarkably decreased compared with that of a homogeneous sphere.

The photorefractive properties of poly(N-vinylcarbazole) doped with a variety of nonlinear optical chromophores and sensitizing agents are surveyed. Steady-state diffraction efficiencies of greater than 10 to the -3 and two-beam coupling gain exceeding the absorption loss are found in six materials combinations. The effect of the structure of the nonlinear optical chromophore on the photorefractive properties is discussed.

To our knowledge only one processing formula for silver-halide sensitized gelatin (SHSG) derived from Agfa-Gevaert holographic plates has been published in the current literature, which is apparently a result of the extremely high degree of hardening of the gelatin emulsion. We propose a modified processing formula for SHSG derived from Agfa-Gevaert plates. The holographic characteristics of the processed SHSG plates were measured and high diffraction efficiency, as high as 80%, and an almost flat spatial-frequency response within the region of interest were achieved. Some of our observations during the experiments are discussed. The behavior of the gelatin emulsion was consistent with the models for processing dichromated gelatin. We observed swelling rather than the shrinkage expected from the removal of the silver-halide grains. This swelling can be controlled by postbaking.

A double-knife-edge method for focusing error detection has been integrated into one molded-glass optical element (MGOE). The first surface of the MGOE consists of two parts, a slant plane and a sphere; the second surface is an asphere. Groove cross noise caused by a geometrical aberration of the MGOE is simulated. When the second surface is at sphere, there is a focus offset of 3 micrometers for a photodetector shift of + or - 10 micrometers, whereas the aspherical surface causes no focus offset. There was less than 0.3-micrometer groove cross noise in the MGOE in the experiment.

A systematic method for the design of antireflection coatings for two widely separated spectral regions has been previously described. This method, based on the buffer layer concept, has been extended to the design of optical coatings with virtually any spectral characteristics in the two regions. To demonstrate the principle, coatings with all possible combinations of the properties of antireflection coatings, neutral filters, reflectors, edge filters and narrow-band filters in the visible and in the infrared spectral regions are presented.

Plasma-assisted chemical etching (PACE) and ion milling (IM), originally developed for microelectronic fabrication, can now be used to shape or figure and smooth or polish optical and other surfaces with the unique advantage of doing so without mechanical contact. Using a recent theory of the temporal evolution of surfaces that is due to arbitrary additive or subtractive microscopic processes, the author critically compares the predicted and observed smoothing of PACE and IM in this paper to provide insight into their smoothing and other behavior. PACE removes >10 cubic mm/min and smooths surfaces of considerable roughness (>10-micrometer rms). It has produced smoothed surfaces to 10 to the third power times slower, is used primarily for making corrections of less than a micrometer, intrinsically generates electronic subsurface damage, and furthermore requires starting with a smooth surface (approximately equal to 1.0 nm) to maintain smoothness. Both PACE and IM remove mechanical subsurface damage. In agreement with observation, it is shown theoretically that the central distinction between PACE and IM stems from substantial differences in their intrinsic smoothing.

The behavior of codeposited thin films of ZnSe/LaF3 and Si/ZnSe has been investigated. Mixed ZnSe/LaF3 films are polycrystalline with intermediate compositions with moderately high compressive stress (15000-2000 kg/cm squared). Mixed Si/ZnSe films are amorphous with intermediate compositions with low compressive stress (< 1000 kg/cm squared). Optical properties of the ZnSe/LaF3 system vary monotically with composition, but those of the Si/ZnSe system do not, which is explained by the possible chemical reaction of the two species.

A polymeric waveguide material with nonlinear optical properties is studied: crosslinked poly(methyl) methacrylate (PMMA) doped with N,N'-dihexyl-amino-nitrostilbene (DHANS). The fabrication and characterization of thin-film waveguides (2-4 [Mu] m) are demonstrated. The anisotropy of the refractive index and the damping of the films have been investigated by m-line spectroscopy and loss measurements. Thin polymeric multilayer structures, including a nonlinear optical core, sandwiched between buffer layers and electrodes have been produced. For these samples, the anisotropy of the refractive index in poled films are measured. Finally, two systems are compared: PMMA/DHANS and a side-chain polymer with the same nonlinear optical group.

We report a simple method for the determination of optical constants in the [lambda] = 10 [Mu] m region. The method is based on the measurement of reflectance over a wide range of angles of incidence by using a [CO.sub.2] laser as the source. Effective values of the refractive index and extinction coefficient at different [CO.sub.2] laser emission wavelengths are determined for alumina, fused silica, and beryllia, materials that are widely used for [CO.sub.2] Waveguide lasers and for [CO.sub.2] laser beam transmission.

Teflon polishing is compared with pitch polishing as a method for achieving supersmooth and flat optical surfaces. Because a Teflon lap wears slowly, it will retain its surface shape to produce extremely flat optical surfaces, [lambda]/100, consistently and reliably for extended periods of time, of the order of days. To compare the two methods, we polished 50-mm-diameter samples of various optical materials, using colloidal suspensions in water on both pitch and Teflon laps under the same polishing conditions. Flatness was maintained to better than [lambda]/10, and roughness less than 10 A rms was measured on all samples by two Talystep surface-profiling instruments, one in the United States and one in Australia, with excellent agreement between measurements made by the two instruments. It was possible to obtain flat and smooth surfaces (

We demonstrate the stretching of 100- fs pulses by a factor of 12,000, using standard-size optical elements. These stretched pulses are then amplified and recompressed to their initial duration. Key words: Femtosecond phenomena, ultrashort pulses., A large stretching factor of femtosecond pulses by a factor of 12,000 is attainable using standard-size optical elements and a correctly designed stretcher. The attainment of 10-GW pulses is already possible for the safe exploitation of the full potential of alexandrite amplifiers, one unit of which is expected to produce 0.5-1-TW pulses.

A direct measurement of the electrogyratory effect in bismuth silicon oxide is performed at wavelengths of 633, 543, and 442 nm. We experimentally measured the electrogyratory effect separately from the electro-optic effect. For externally applied electric fields ranging from 0 to 60 kV/cm, the contribution due to the electrogyratory effect is found to be negligible with respect to the contribution due to the electro-optic effect. Since devices employing bismuth silicon oxide typically require applied electric fields in this range, the electric field dependence of the rotary power is shown not to perturb the desired operation.

Continuous testing at room temperature of large optics made of Zerodur has revealed a delayed elasti effect under low stress levels during both load and recovery after removal. Using a high-performance mechanical profilometer, a delayed strain of the order of 1% is realized over a period of a few week time-dependent phenomenon is elastic and reversible, but must be accounted for in various applicatio optical design. Key words: Delayed elasticity, Zerodur, room temperature., A delayed elastic effect in large optics made of Zerodur under low stress levels was revealed after continuous testing of the materials at room temperature. The effect was observed during both load and recovery after removal. A delayed strain of th order of 1% is realized after some weeks with the use of a high-performance mechanical profilometer. The effect is fully reversible within measurement capability but should be accounted for when measuring to the optical tolerances of a fraction of light wavelengths.

A general formula is presented for the index measurement of isotropic media. The significance of knowing the beam angle inside anisotropic and nonlinear media for measuring the ordinary and extraordinary refractive indices and the nonlinear susceptibility tensor components is described.

We believe that, for the first time, the UV-visible optical reflectivity of nanocrystalline ceria with various particle sizes has been measured, and their optical absorption characteristics have been studied by Kramers-Kronig transformation. The wide absorption band in the 200-480-nm range consisted of two narrow bands. This wide band was designated as the charge transfer of [O.sub.2p]-[Ce.sub.4f] while both narrow bands, which overlapped in this wide band, were due to the well-known 2[F.sub.5/2]-2[F.sub.7/2] spin-orbit splitting of the Ce 4[f.sup.1] state. With a decrease in the particle sizes of the samples, the bandwidth expanded distinctly and a red shift in the wide band was observed. On the other hand, the band gap between the narrow bands showed a remarkable increase. All of these phenomena resulted from the effects of quantum size and the interface of nanostructured materials. Key words: Optical properties, nanocrystalline ceria.

Long-term dc drift of lithium niobate optical intensity modulators is successfully reduced by exclusion of O[H.sup.-]ions from the lithium niobate substrate, In this regard, the titanium-indiffused waveguide is prepared on a commercial OH-free substrate under a dry gas atmosphere. The dc drift measured for these hermetically sealed modulators indicates a possibility for continuous operation over 20 years at 50 [degrees] C.

The cubic nonlinear susceptibility of barium metaborate was employed for the generation of phase-matched third-harmonic generation (THG) of 1.053-[Mu] m pump radiation. The various processes that are responsible for THG in this crystal are discussed and experimental results for types I and II phase matching are presented. THG power of 50 [Mu] W is recorded with an average pump power of 800 mW of 1-kHz repetition rate picosecond pulses.

The surface-plasmon resonance (SPR) technique is used to study the growth rate and the nature of [Ag.sub.2]S films formed on a silver (Ag) film exposed to an atmosphere containing 50% [H.sub.2]S for different times. The thickness of the [Ag.sub.2]S layer formed, estimated from shifts in the experimental SPR curves, showed a saturation tendency after an initial linear increase. Theoretical analysis of the curves when Ag and [Ag.sub.2]S are treated as two uniform layers and Ag-[Ag.sub.2]S as a composite layer showed that radiation damping is mainly responsible for the increase of half-width and dip reflectance, indicating that the [Ag.sub.2]S film formed is rough and discontinuous. [C] 2000 Optical Society of America OCIS codes: 240.5770, 240.6680, 240.0310, 260.3910, 310.6860, 310.6870.

Thermal analysis for a UV light-curable epoxy adhesive material recently commercialized by Daikin for assembly of optical fiber devices with a low optical reflection was performed. This epoxy was used in the assembly of LiNb[O.sub.3] waveguide devices; previous reliability tests measuring mechanical and optical characteristics confirm the stability of this epoxy for the fiber connection. However, due to an intrinsic characteristic of the material, polymerization by a curing process on the device assembly line was incomplete, and additional polymerization was expected to occur after assembly. Here, the duration necessary for complete polymerization of this adhesive material is estimated experimentally to be 1.8 years at 80 [degrees] C. Further, the activation energy for such additional polymerization is derived to be 0.38 eV ([approximately] 0.4 eV, considering measurement errors).

The dc drift of LiNb[O.sub.3] (LN) optical intensity modulators is experimentally investigated from the viewpoint of the repeatability of the phenomenon. The drift has been assumed to be reversible and be independent of the magnitude of the applied dc bias. However, a bias voltage dependency of the dc drift is experimentally manifested here, especially under a high bias voltage. By an iterative dc bias application for the same LN modulator, the drift rate is increased, and a hysterisis appears in the drift/recovery cycles.

A self-compensation method for measuring the birefringence of an optical material is proposed; an accuracy of [Difference] [10.sup.-6] is obtained. Only a thin sample is needed in this method.