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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.

Behavior of the steady-state photorefractive harmonic gratings and the space-charge field spatial distribution are derived without restrictions. This is accomplished by solving the shallow-trap-model material equations.

It is shown that transmittance through a metal film with subwavelength holes exhibits sharp resonances corresponding to the excitation of various surface waves. Results for local electromagnetic fields and the extraordinary optical transmittance (EOT) are discussed, and theoretical results are compared with experimental observations.

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.

Research describing the characterization of the semiorganic non linear optical material sodium p-nitrophenolate dihydrate is presented. In particular the thermal expansion, specific heat and dielectric properties are investigated.

Research describing three electrochromic devices for thermal emittance modulation is presented. Polycrystalline and amorphous tungsten oxide are incorporated in the design of these single and double grid, and polymer-based emissivity modulation devices.

A new study compares the measured and calculated energy transfer rates of the 4S3/2 state of the Er3+ ion on the ErF3 concentration in flurozirconate glasses.

The results are described of an electron paramagnetic resonance investigation into three platinum centres induced in potassium titanyl phosphate by ionizing radiation.

Ab initio methods are used to calculate the electronic excitation energies of 16 azobenzene dyes.

The compound K4Ln2(Co3)3F4 (Ln=Pr, Nd, Sm, Eu, Gd) has an acentric crystal structure.

Spectroscopic studies of Pr3+:Yb3+ codoped lead fluoroindogallate glasses were conducted. The objective was to show that Yb3 -> Pr3+ energy transfer mechanism enhances the infrared emission of PR3+ in lead fluoroindogallate glasses. Results revealed that Yb3+:Pr3+ codoping of lead fluoroindogallate glasses enhances the intensity of the 1.3 micron Pr3+ emission up to 40 times through the Yb3+ -> Pr3+ energy transfer.

A study on Cr4+-doped yttrium aluminum garnet as an absorber medium for Nd lasers was conducted to derive more realistic values of ground state absorption and excited state absorption cross sections to serve as input parameters to the theory. The Z-scan technique was used to gauge both cross sections in several Cr4+-doped yttrium aluminum garnet samples at temperatures ranging from -60 degrees C to 98 degrees C. Results are discussed.

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.

Optical materials for vacuum ultraviolet optics have attracted strong research interest as ArF excimer laser lithography of semiconductors has entered the practical application phase since 1996. A study was conducted to investigate ArF excimer-laser solarization in P-free and doped AlF3-YF3-RF2, R = alkaline earth metal, glasses by optical absorption and electron paramagnetic resonance spectroscopies. Results are discussed.

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.

Research was conducted to examine the refractive indices of the optically nonlinear organic crystal (S)-3-methyl-5-nitro-N-(1-phenylethyl)-2-pyridinamine. The refractive indices were measured from 480 to 660 nm and fitted to four-parameter Sellmeier equations with an accuracy of +/-3 x 1/10 to the 3rd power to +/-5 x 1/10 to the 3rd power. The values of the n(sub x), n(sub y) and n(sub z) refractive indices at 532 nm were found from the Sellmeier equations to be 1.690, 1.901 and 1.725, respectively.

The influence of clustering effects on the susceptibility of composed materials is considered by means of a generalized method of integral equations in the case of a two component medium. For the first time the discrete character of the impurities and of the host medium are both taken into account. We have shown that the clustering of the impurities influences the susceptibility of the composite material in all mixtures except for the case when the host medium is a vacuum. The developed approach may be applied to artificial magnetic materials and to photonic band-gap structures in the long wavelength limit. Index terms - Nonhomogeneous media, dielectric materials, optical materials.

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.

The effects of strain and quantum confinement on the electronic band structures, density-of-states and optical gain spectra for wurtzite GaN-AlxGa1-xN quantum-wells were investigated by progressively increasing the aluminum mole fraction in the barrier material. Results showed an improvement in the TE optical gain and a suppression in the TM optical gain when the aluminum mole fraction increases. Moreover, the modal gain was improved when the well width was reduced.

Researchers calculated the optical absorption spectra of Er3+ in Ga2S3-GeS2-La2S3 glasses using Judd-Ofelt theory and lifetime data. The spontaneous emission probabilities are greater than those of other glass systems. They are five times larger than those of ZrF4-based fluoride glass, due largely to the sulfide glasses' large refractive indices. The sulfide glasses also generally have a high quantum efficiency, due partly to their low phonon energy, but the quantum efficiency of 4S3/2 level is much lower than that of fluoride glass.

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.

Molecular-based magnets have low density and this, with their weak color, mean they have potential in magneto-optical devices. This research is aimed at investigating molecular-based magnets and their optical properties, relating this to their magnetic properties. The temperature range used is 4-300 degrees Kelvin. There is a complementarity and consistency between magnetic and optical techniques for MnIICuII paramagnetic molecules. There is a need for further research on the impact on optical properties of long-range magnetic ordering.

A new class of laser materials based on tetrahedrally coordinated Cr2+ ions as dopants in II-VI crystals are analyzed. Spectroscopic data relevant to the understanding, design and engineering of lasers based on the materials are examined. The materials represent the first widely tunable diode-pumpable mid-infrared lasers functioning at room temperature. The materials are major components for the expected realization of compact, diode-pumped Cr2+ lasers.

Two factors explain the greater increase in molecular hyperpolarizability produced by N-phenyl substitution of 4-nitroaniline, compared with N-methyl substitution. These are the larger perturbation in the energy of the donor orbital by the phenyl substituent and the additional contribution of pi-electron density from the phenyl substituent to the HOMO in one of the amine and phenol/ether derivatives. In contrast, O-phenyl substitution of 4-nitrophenol produces a smaller increase in hyperpolarizability than O-methyl substitution.

Amorphous polymers with strong second-order optical nonlinearities contain molecular chromophore dipoles as guest molecules, as side groups, or as main-chain segments. In order to break the inherent centrosymmetry of the initially isotropic dipole orientation in these materials and to render them nonlinear optically active (as well as piezo- and pyroelectric), preferential dipole alignment by means of electrical poling is necessary. After poling, the nonlinear optical polymer films are molecular dipole electrets so that the full range of techniques for the preparation and investigation of polar electrets may be employed, together with nonlinear optical techniques, originally developed for the investigation of ferroelectric polymers, such as poly(vinylidene fluoride). The field of nonlinear optical polymers developed from very enthusiastic beginnings in the early eighties to the present and more realistic approach, with real applications just about to appear.

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.

The self-assembly of 4( 4- N,N-bis hydroxylethyl amino phenyl azo)pyridine into second-order nonlinear optical mono- and multilayers bearing the (aminophenyl)azo pyridinium chromophore were carried out. The superlattices, according to spectroscopic studies, were found to possess smooth surface morphologies, very high second-order nonlinear optical susceptibility, photochemical stability and thermal robustness.

This paper investigates a method to compensate for thermal distortions which occur during pulsed laser welding of optical packages. A control strategy, based on the use of a fast response piezo-actuator to maintain relative alignment between the fiber and the laser in the critical time period after application of the laser pulse and before cooling of the weld nugget is described.

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.

Lifetimes of metastable levels of chromium in ruby are determined using an unusual technique. The fluorescence from the chromium is measured using an ac technique in which the excitation is modulated and the fluorescence is detected synchronously. The novelty lies in the measurement of the dependence of the signal on the modulation frequency and extracting the lifetime from the frequency dependence. The experiments and data analysis demand a detailed understanding of the methods of lock-in amplification and synchronous detection and hence they can serve as a useful primer on the subject. The observed values for the lifetimes show excellent agreement with previous measurements.