Recent experiments that measure the effects of the photoinduced generation and transport of charge on the refractive index of polymeric films having a second-order nonlinear optical response are reported. Two approaches were taken to observe these effects. In the first approach, the photoconductive and light refraction processes were separated by confining these functions to separate layers in a multilayer structure. In the second approach, photoconduction and refraction functions were combined in the same layer. The modulation of the refractive index was then measured in response to photoconductions.

Bismuth tellurite (Bi2TeO5) is a new photorefractive material that is now available as single crystals of high optical quality. The results of measuring the photorefractive properties of Bi2TeO5 crystals are reported and the properties of this material are compared to those of well known photorefractive crystals. The decay of the photorefractive signal in Bi2TeO5 has multiple components and several different contributions to this signal were identified. One of the components has a lifetime of months and therefore has potential for holographic memory applications. This long-lived photorefractive signal is attributed to ion displacements and it can be produced by both continuous wave and short pulse write beams. Several experimental conditions were investigated to enhance this photorefractive signal.

Obtaining self-pumped phase conjugation in photorefractive crystals without the use of external mirrors usually requires that the crystals exhibit significant beam fanning and have large gain-length products. Large variations in the phase conjugate reflectivity and response time can occur with changes in the incident beam location relative to the corner cube. This paper explores experimentally the dependence of the phase conjugate reflectivity and the response time on the incident beam location in a Ce-doped SBN:60 crystal. Beam erasure at selective sites within the crystal is used to determine the location of the self-organized gratings.

The experimental evidence of slow absorption grating formation in a photorefractive BTO crystal is presented. The absorption grating is recorded together with the usual photorefractive one during the long exposure time in a self-stabilized holographic setup. Due to the different nature of both gratings (the amplitude grating is assumed to be isotropic) the analysis of the polarization state of the diffracted beam allows the authors to prove the existence of an absorption grating. The strong two-wave mixing influence on the hologram readout process is demonstrated.

This paper investigates the effects of thermal light-scattering fluctuations and demonstrates that these are the dominant noise source inherent in photorefractive and electro-optic media. Fundamental noise limits to dynamic range and channel capacity are determined. Two sources of light-scattering fluctuations are examined: (1) thermal fluctuations in the space-charge field, which induce corresponding fluctuations in the dielectric constant through the electro-optic effect, and (2) fluctuations associated with the optical Kerr effect. Calculations are present for BaTiO3 and several other materials and are discussed in light of recent experimental measurements of dynamic range. Our results suggest a very large dynamic range for photorefractive materials (120 - 140 dB) that should prove useful for optical signal processing applications.

Potassium titanyl phosphate (KTP) has been used to frequency double the 1.32 micrometers output of a Q-switched Nd:YAG laser. Up to 40 mW of average power at 659 nm was obtained using a conventional intracavity doubling approach. A second intracavity doubling scheme was also demonstrated in which KTP served simultaneously as the frequency doubling crystal and as the substrate for one of the resonator mirrors. Although the second harmonic power using this technique was limited by heating in the crystal, the approach shows promise.

The cyanine dye (Cy) was embedded in (or absorbed by) a monolayer on air-water interface and its multilayer samples deposited on glass slides were obtained. The studies of their absorption spectra showed that Cy in LB films formed H-aggregates. Multiple phase conjugate waves induced by third- and higher-order nonlinearity of the LB film were observed. High to third-order diffractions with two-beam-interaction and self-phase modulation phenomena with single-beam-interaction in the LB film were also observed. The exceptionally large third-order susceptibility was measured to 5*10^-8 esu for the LB film, which is larger than that deduced from measured third-order byperpolarizability of Cy monomers in bulk solution. The origin of this large third-order susceptibility for the LB film, due to the near-resonant and delocalized exiton enhancement in the aggregates, is duscussed as well.

The development of the techniques to control the light flux parameters directly by the light itself has permitted us to realize the new class of devices designed for completely optical signal processing. These new devices are both one-channel facilities for fiber links (light- control switches, modulators, and optical transistors) and multichannel ones (spatial-time light modulators -- STLM), which are the basic elements for the systems of optical data processing. All of these devices are based on light-control optical elements, in which one light flux or impulse directly controls parameters of another without doing an intermediate conversion into the electric signal and back again. In order to transfer some data from the control light flux to the fundamental one, a certain optical medium is required where the transmission properties depend on the control light. Scientific work on creation of the optical medium has already been carried out for more than 20 years. By now, sensitive media with specific switching energy of E equals 10^-6 + 10^-8 J/cm² and switching rate of (nu) <EQ 10² cycles/s (the structure like MLS-liquid crystal) have been created. The devices for multichannel optical data processing -- that is, STLMs -- are implemented on the base of these sensitive media.

This paper considers the temperature dependence of linear polarized light on a thin crystalline plane parallel cadmium diphosphide plate. The experimental and calculated results show the possibility of controlling the bistable characteristics of interferometer.

In this paper, the three-wave interactions in a nonlinear dissipation medium are researched and three conclusions obtained. (1) The three-wave interactions may give bifurcation and have chaotic solutions. Chaotic criteria are given for less dissipation of pump wave. (2) The stable and analytical asymptotical solution is obtained for more dissipation of pump wave. (3) The stable asymptotical solution and the criteria of Hopff bifurcation are obtained and the Hopff bifurcation may make the transfer of momentum and energy.

The equations describing the ultra-short pulse dynamics are represented including the transverse effects caused by both self-action and modes of the continuous transverse-wave- numbers spectrum.

Dynamic surface gratings created by two-beam interference on the structure supporting guided waves are considered. The bistable and trigger type behavior of the steady state grating, caused only by the electrodynamics peculiarities of the guided waves excitation at a magic angle of the laser beams incidence, are defined.

In this paper, an attempt is made to study the Burstein-Moss shift in quantum wells, quantum wires, quantum dots, magneto quantized, and magneto-size quantized-layers of nonlinear optical materials, by formulating the appropriate electron statistics. It is found, taking CdGeAs₂ as an example, that the Burstein-Moss shift exhibits oscillations in terms of non- ideal Heaviside step functions for quantum wells, wires, and dots with respect to doping and film thickness respectively. The Burstein-Moss shift also exhibits various oscillations for the last two types of quantum confinement of band states with respect to electron statistics and quantizing magnetic field respectively. The variations depend essentially on the energy band structure of the materials and the simplified theoretical formulation is in agreement with experimental results given elsewhere.

In this paper, an attempt is made to investigate the photoemission from superlattices of nonlinear optical materials with graded interface in the presence of a strong magnetic field within the framework of k.p formalism by considering various types of anisotropies of the energy spectrum. We have also compared the same emission from the constituent materials by formulating the respective expressions. It is found by considering CdGeAs₂/Cd₃As₂SL as an example that the magneto photoemission exhibits oscillatory magnetic field dependences, due to the SdH effect and increases with increasing photon energy in a ladder- like manner. The theoretical formulation is in quantitative agreement with experimental observations reported elsewhere. In addition, the well-known expressions for the photo- emission from relatively wide band-gap non-degenerate materials have also been obtained from the present generalized theoretical analysis under certain limiting conditions.

A fully quantum theory for the general case of any higher order optical harmonic generation associated with resonance absorption of pump photons is presented. The treatment utilizes density-matrix formalism based on the Scully-Lamb model, both atomic system and radiation fields being quantized. Detuning, homogeneous and inhomogeneous broadening and relaxation parameters are included. Coherence characteristics and build up of the harmonic fields are discussed for different initial distributions. The Doppler limit restriction has been lifted and the possibility of a relatively efficient conversion of harmonic photons of higher orders is discussed.

Since the large third-order optical nonlinearity of organic metal (alpha) -(BEDT-TTF)₂I₃ was reported by Huggard et al. in 1987, the nonlinear optical properties of organic metals have received great attention. New synthetic routes for metal-dithiolene complexes were developed in the last decade and several of the complexes which have a TTF-analogous structure proved to be good electrical conductors. THG activities of solutions of some of these metal-dithiolene complexes were measured by using a THG Maker fringe method. For example, the (Chi) ⁽³) value of a 0.2 wt% DMF solution of Ni(dmbit)₂TBA at 0.1 mm thickness was measured as 7.2 X 10^-14 esu by using 1,319 nm Nd:YAG laser light. In this measurement the (Chi) ⁽³) value of 2.8 X 10 ^-14 esu for the SiO₂ glass was used as a reference. From this measurement a (Chi) ⁽³) value as large as 3.6 X 10^-11 esu is predicted for the neat compound.

In the future optoelectronic integrated circuits (OEICs) are destined to evolve into sophisticated functional circuitry upon which a multiplicity of applications will be based, such as: optical communications, optical interconnects, optical computing, optical memory, laser printing and scanning, visual displays, pattern recognition, and neural networks. This evolution of OEICs involves the integration of phototransmitters (semiconductor lasers and light-emitting diodes), photoreceivers (photodetectors and phototransistors), spatial-light modulators, transistors (bipolar and field-effect), diodes, resistors and capacitors, and micro- optic components (e.g., micro lenses). We describe our efforts to date and future directions which are concentrated on the integration of vertical-cavity surface-emitting laser diodes (VCSELs) with transistors, photoreceivers, and micro-optic components. VCSELs, which may be patterned in high densities (over a million in a square cm) and emit light perpendicular to the plane of the substrate, have an ideal light-emitting geometry for the above mentioned applications and for integration with micro-optic components. We describe our efforts to develop monolithic surface-emitting laser logic devices, which we refer to as CELLs, consisting of phototransistors, current controlled bipolar transistors, and voltage-controlled field-effect transistors integrated with a VCSEL to form optically and electrically addressable photonic switching devices having high contrast. We also discuss the integration of micro- optics with VCSELs. Finally, we describe combinations of OEIC components and subassemblies and their applications to several of the above mentioned photonic switching applications.

We summarize our ultrafast switching results in GaAs multiple quantum well directional couplers and report on coherent pulse propagation in single strip-loaded GaAs multiple quantum well waveguides. The transmitted pulse shape is measured by sum frequency generation cross-correlation and compared with calculations based on the coupled semiconductor Bloch and Maxwell's equations.

We have investigated vertical transport in two different multiple quantum well (MQW) semiconductor optical switching elements; a self electro-optic device and a waveguide directional coupler, using picosecond resolution pump-probe measurements. Cross-well charge transfer mechanisms in semiconductor MQW structures are basic to the operation of a number of optical switching devices currently being researched for applications in signal routing, optical processing, and computing. The cross-well motion of charge carriers in multiple quantum wells, and specifically how rapidly photogenerated carriers can be ejected from quantum well, sets the fundamental limit on the speed of operation of some devices and can be employed to speed the recovery time of others. A self-consistent, time and spatially resolved model of cross-well transport gives good agreement with experimental results. The use of cross-well carrier sweep-out is shown to give significantly improved recovery times for all- optical waveguide directional coupler switches.

This paper reviews electro-optic effect devices (SEEDs). Included in this are the resistive and photodiode biased devices and a discussion of the symmetric SEED. We describe the performance of symmetric SEEDs and the extension of these devices to Logic SEEDs that can be custom designed to perform complex logic functions such as photonic switching nodes and optical shift registers. Lastly, we review recent progress in the integration of SEEDs and GaAs metal-semiconductor field effect transistors (MESFETs).

We have investigated several nanosecond nonlinear switching mechanisms in carbon microparticle suspensions. These switching mechanisms are based on combinations of effects such as plasma scattering and cavitation-induced total internal reflection (TIR). The contributions from each of these effects is studied. The dominant nonlinear switching mechanism in the majority of these samples is laser induced cavitation which leads to TIR switching. This occurs when the incident laser energy that is absorbed by a carbon particle is sufficient to heat up and vaporize a small volume of the suspending liquid forming a microbubble. TIR switching is observed when these vapor bubbles expand to dimensions that are similar to the transverse dimensions of the incident beam and form a glass-vapor interface at the front substrate surface. Using this mechanism, nonlinear refractive index changes as large as 0.3 have been experimentally obtained on a nanosecond time scale using low power, Q-switched, frequency doubled ((lambda) equals 0.532 micrometers ), Nd:YAG laser pulses.

We present the nonlinear interface optical switch in the context of digital optical computing applications. Implications with regard to materials design and development and switch evaluation are discussed. A specific class of materials synthesized using laser chemistry of organometallics is presented. Embodiments of this type of switch have considerable potential for meeting many of the required design criteria for practical implementation of digital optical computing devices.

We review some earlier work on parallel image subtraction and present new experimental results on shift-invariant parallel subtraction of the Fourier power spectrum of two images. The subtraction is achieved by employing a real-time holographic Mach-Zehnder interferometer with a photorefractive crystal.

No abstract available.

The self-pumped ring phase conjugation using reflection gratings in Kerr media is investigated. The results show that with a ring cavity, self-oscillation occurs at a certain threshold intensity which is lower than that for the conventional stimulated Brillouin scattering process. The effect of cavity detuning on phase conjugation reflectivity and frequency shift is also discussed.

We present numerical simulations of transverse stimulated Brillouin scattering (SBS) in large aperture optical elements and investigate its suppression due to finite laser bandwidth. A specific model for the laser bandwidth, namely, a sinusoidal phase modulation of the electric field, is considered. Our calculations indicate that bandwidths larger than the SBS linewidth lead to significant reduction in the SBS gain. We also investigate the dependence of the SBS gain on the modulation frequency and find that for a fixed overall bandwidth, a modulation frequency of the order of the SBS linewidth leads to an optimal reduction of the SBS gain.

We have designed and are testing a `fail safe' system on Nova to suppress stimulated Brillouin scattering (SBS) in large optics at the output of the laser. The system increases the laser bandwidth to prevent SBS and prevents pulses with insufficient bandwidth from being injected into the amplifier chain. It is thus fail safe. The system design and experimental measurements are presented.

The fluid equations governing medium response to stimulated Brillouin scattering (SBS) are solved in the quasi steady-state approximation to obtain the gain of the scattered signal as a function of changes in the large-scale velocity and temperature of the medium. These equations are coupled with the field amplitude equations in one dimension to obtain the scattered signal intensity at each time step in the incident pulse. After calculating the incident and scattered pulse intensities at each z step for a given time step, the change in the large-scale fluid variables for the next time step is determined by finite difference. During the early history of the pulse, the frequency shift between the incident and scattered waves is such that the scattered wave has maximal gain. As the pulse evolves, second order terms in the fluid equations cause large-scale motion of the medium as well as the oscillatory motion associated with the acoustical wave. This large-scale motion causes a Doppler shift in the resonance condition of the medium such that the scattered signal no longer has maximal gain. Second order terms in the fluid equations also result in large-scale heating of the medium which affects the resonance condition by increasing the acoustic velocity, thereby causing further reduction in scattered signal gain. A few calculations were run using parameters corresponding to an experiment performed by Dolgopolov et al. involving a single pulsed iodine laser (wavelength 1.315 microns) incident upon a 70 atmosphere nitrogen cell. Although the gain near the front of the interaction region was greatly reduced during typical pulse times (5 - 10 microsecond(s) ec), there was no substantial impact on the final scattered wave intensity since the reduction in gain did not occur until after this signal had grown to high intensities. This gain reduction merely had the effect of shortening the effective interaction region by a few gain lengths, and could not explain the drastic reduction in scattered wave intensity observed at incident pulse intensities exceeding 1000 MW/cm² in the Dolgopolov experiment. Contrary to our initial hypothesis, it appears that nonlinear terms in the fluid equations governing medium response to SBS have little effect on scattered signal intensity or phase conjugation fidelity in the case of single pulse experiments. However, the predicted large-scale fluid motion and heating can propagate as an acoustical pulse long after the decay of the incident laser pulse, which may affect the scattered signal fluence of future pulses in a pulse train. A three-dimensional large-scale fluid model would be required, however, to properly analyze this effect.

Seeded, transient, stimulated Brillouin scattering (SBS) is studied using a new non-iterative, numerical algorithm to solve this two-point boundary value problem. The coupled pump, Stokes and phonon equations are solved numerically, including the effects of pump depletion and a finite phonon lifetime. The non-iterative approach leads to efficient computation (< 30 sec of cpu time, VAX 8000 series computer for 500 by 5000 points in space and time respectively). The numerical study predicts transient oscillations in the pump and the Stokes intensities. The frequency of these oscillations depends on the phonon lifetime and the depleted, exponential SBS gain. This work is the first known prediction of these oscillations.

A two-cell stimulated Brillouin scattering (SBS) pulse compressor design is presented that can be scaled to large laser pulse energies and a numerical model has been developed which accurately predicts the performance of this pulse compressor system over a wide range of operating parameters. The compression of a 2.5 J input pulse from a width of 15.8 ns to 1.7 ns is demonstrated with 80% energy efficiency.

The shot-to-shot phase fidelity of an SBS phase conjugator operated many times above threshold has been found to be very sensitive to the slope of the leading edge of the input pulse. For a pulse with a rising edge that is short relative to the acoustic lifetime of the SBS medium, strong random fluctuations in the fidelity of the wavefront reversal are observed. However, by tailoring the leading edge of the pulse relative to the acoustic response time of the medium, good phase reproduction can be achieved. No increase in shot-to-shot fidelity fluctuation was observed using a carbon tetrachloride SBS cell at input energies up to 100X threshold, resulting in reflectivities of 90%. Conclusions are made about the source of the observed random fluctuations which are supported both by experimental measurements and numerical modeling.

We have experimentally determined the spectrally noncritical phasematching behavior of Type I frequency doubling in KDP and its dependence on deuteration level in partially deuterated KDP. The first order wavelength sensitivity parameter (alpha) (Delta) k/(alpha) (lambda) for Type I doubling of 1.053 micrometers light vanishes for a KD^*P crystal with a deuteration level between 10 and 14%. Very high bandwidth frequency doubling of Nd:glass lasers is possible with such a crystal.

We review the noise characteristics and the low-light-level imaging capabilities of a stimulated Raman amplifier and show how these properties can be combined with time-gating capabilities to image through dense scattering materials. Using 30 psec time-gating pulses, images were obtained of a resolution bar chart viewed through either a suspension of 0.364 micrometers polystyrene spheres where the forward attenuation due to scattering was e²⁸, or though a non-dairy creamer solution where the attenuation was up to e³³. At the highest scattering attenuation levels these images could not be detected by any conventional imaging method.

When a principal atomic transition (dipole allowed from the ground state) is driven by odd- multi-photon excitation or by stimulated hyper-Raman scattering, a nonlinear multi-wave mixing field is generated at the transition frequency. A number of dramatic effects on such odd-photon mediated processes can ensue as a result of the internally generated wave-mixing fields. Excellent agreement between theory and experimental studies in Xe and in metal vapors is illustrated for a number of predicted effects including: suppression and strong shifting of resonance lines and hyper-Raman emissions under single and multi-laser excitation. We illustrate the dependence of the interference-related effects on pressure, oscillator strength, wavelength combination and relative propagation directions of pump laser beams. Contrary to most other nonlinear effects, we show that none of the features (in the semi-classical regime) depends on the intensity of the driving laser field.

Theoretical and experimental studies of the structure of the thermal lens generated in a liquid by a Gaussian electromagnetic field are performed. It is shown that the light induced thermal lens can be considered a focal source of light plus a ring of light sources located on different planes.

Effects of stimulated Raman scattering on the distributed erbium-doped fiber amplifier are studied numerically. The pump wavelength is 1.48 micrometers and the signal wavelength lies between 1.52 micrometers and 1.57 micrometers . The competition between the gain from stimulated Raman scattering and the gain from the pumped erbium ions is shown. It is found that the signal gain is enhanced by SRS except for the signal near 1.53 micrometers .

In this paper, we discuss recent results on the propagation of dark spatial solitons (DSS). Dark spatial solitons are particular solutions of the nonlinear Schroedinger (NLS) equation modeling propagation of light beams in optical Kerr media. Experimental results are presented for three systems, including sodium vapor, various thermally nonlinear liquids, and the bulk semiconductor system ZnSe. The results of these investigations indicate that experimental dark spatial solitons obey the conservation laws of the NLS equation, possess collision properties characteristic of the theoretical DSS solutions, and are stable to external perturbations induced by the experiment. In addition, through an interferometric technique, we investigate the phase profile of the dark spatial solitons and show that it is in good agreement with the NLS solution. In addition to the fundamental DSS, we have performed experiments where nonfundamental DSS are excited in pairs by making use of an even initial field profile as originally discussed by Zakharov and Shabat. The transverse velocities of the solitons excited in the is manner are measured and found to be in good agreement with those predicted theoretically.

It is now well known that a novel class of solid-state integrated devices in radar, electronic warfare, and communication systems can be constructed using linear or nonlinear magnetostatic guided waves or surface waves as their basis. Such waves can propagate in magnetic thin films in the microwave bands. The liquid phase epitaxy (LPE) technology now exists for the preparation of high quality thin films in the microwave bands as well as high quality thin films of yttrium-iron-garnet (YIG). This fact permits the construction of devices in integrable compact form with very low loss. In this review, important theoretical foundations based on the perturbative wave-mixing method for nonlinear magnetic interactions are laid. The second-order magnetic effects may result in the resonant forced second-order nonlinearities. The third-order self-action effects may lead to longitudinal modulation instability and possible soliton formation. The third-order wave-mixing effects can be used to generate phase conjugated wave for signal processing and communication applications. The potential of these nonlinear magnetic effects for new nonlinear microwave devices is very briefly discussed.

All-optical phase modulation in single crystal waveguides of a polydiacetylene has been investigated by two different interferometric methods: Mach-Zehnder and Sagnac. Large phase changes (> (pi) ) have been observed in a short waveguide (2 mm) for a relatively low optical intensity (-10 MW/cm²), at the wavelength of 1.06 micrometers . These phase changes are due to the off-resonant nonlinearity having an ultrafast (< ps) response time. The results are important in terms of all-optical device applications of these materials. The resonant nonlinearities of these materials were previously studied in detail. The present research is focussed on the off-resonant nonlinearity the origin of which has not been understood as yet.

In order to design new organic NLO materials with both higher nonlinear optical susceptibilities, and reasonable optical loss characteristics, it is necessary to understand how different organic structural elements affect the nonlinearity of materials at the molecular level. Only recently, synthetic research groups have begun to devote the time and effort necessary to produce very pure model compounds of systematically varied structures for carefully controlled NLO measurements. In this presentation experimental results and the structural- NLO property trends developed from them are reviewed for the systematic investigations appearing in the literature with emphasis placed on studies conducted by our research group. With these results in mind, some new ways of looking at such organic molecular structures are presented with the intent of stimulating creative thought for novel NLO molecular design.

Several approaches have been suggested during the past few years for increasing third order nonlinearity in organic compounds. In general, these have focused on manipulation of the effective conjugation length of the pi-electron framework to maximize orbital overlap. It has only recently become apparent that substituent effects, which affect the overall electron density distribution, may be an extremely effective way of enhancing nonlinearity. In this study we review known substituent effects on nonlinearity, and suggest how donor-donor, acceptor- acceptor, and donor-acceptor interaction can be utilized in the design of molecules and polymers with enhanced nonlinearity.

Polyimides possess interesting nonlinear optical properties. The overall goal of our effort is to develop the requisite synthesis and processing techniques to produce polyimides with high (Chi) ⁽³) and low absorptive losses. The target value for many applications is (Chi) ⁽³)/(alpha) equals 10^-7 esu-cm. The synthesis and characterization of both the linear and nonlinear optical properties of these materials and the requirements for their utilization in optical bistability is reported.

Synthesis and characterization of covalently bound self-assembled 5,10,15,20-Tetra(4- pyridyl)-21H,23H-porphine (TPyP) monolayer superlattices on various oxide surfaces such as fused silica, glass or silicon are described. The monomolecular thin film structures are characterized by UV-visible ((lambda) _max equals 447 nm) and FTIR-ATR spectroscopy. In addition, x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) studies are used to confirm the formation of a self-assembled monolayer on the fused- silica surface. Attractive features in these complexes are their second-order nonlinear optical properties, which are enhanced by the completely delocalized (pi) -electrons. Second harmonic generation measurements have been used to determine the uniformity of the film, the relative and absolute magnitudes of nonzero elements of the nonlinear susceptibility, (Chi) ⁽²), and the average molecular orientation of the chromophores.

Multifunctional properties of nonlinear optical chromophores are discussed both in terms of a given chromophore exhibiting more than one type or mechanism of optical nonlinearity and in terms of a chromophore exhibiting useful auxiliary properties. For materials exhibiting more than one type of mechanism of optical nonlinearity, the concept of pulse-controlled optical nonlinearity is introduced and discussed. An analogy is drawn to multidimensional nuclear magnetic resonance studies which are useful in systematically elucidating excited state dynamics. Practically, pulsed control of optical nonlinearity provides a means of enhancing and modulating nonlinear optical phenomena. The photochemical reactivity of nonlinear optical chromophores is discussed in terms of fabricating ordered lattices appropriate for the development of integrated circuits and the realization of specific effects such as quasi-phase matching in second harmonic generation.

Time-resolved degenerate four-wave mixing studies were conducted on solutions of transition metal complexes using 35 ps and 1.2 ps lasers at 1064 nm and 597 nm, respectively. The structure of these complexes consists of a transition metal linked to two ligands of o- aminobenzenethiol or benzenedithiol in a square-planar configuration. This study explores the relationship between molecular structure and optical properties in these simple metal complexes. Structural alteration by metal or ligand substitution shows a pronounced effect on both the linear and nonlinear optical properties of these metal complexes. Several nonlinear optical mechanisms are discussed.

In an effort to better understand the relationship between molecular weight and third-order nonlinear optical activity for condensation polymers, a series of oligomeric thiophene containing benzobisthiazoles were synthesized via a trimethylsilylpolyphosphate catalysed condensation of a bis-o-aminothiophenol monomer and a didecyloxythiophene dicarboxylic acid. The physical and chemical characterization of these oligomers, including molecular weight determinations, are summarized. The enhancement of the bulk susceptibility and second molecular hyperpolarizability are demonstrated to increase with increasing oligomer length. Based on the data from femtosecond degenerate four-wave mixing experiments the second hyperpolarizability of the oligomers is enhanced by two-photon resonance.

A self-injection locking system was disclosed in United States Patent #4,982,406 dated Jan. 1, 1991. The device internally narrows a prepulse of a laser cavity before it is replicated as the laser output. This system contains two quarter wave plates, an air spaced etalon, and a polarizing beam splitter. The air spaced etalon separates the off-center frequency signals from the center frequency signals. This is done by inducing a phase shift. Following this, the polarizing beam splitter impedes the off-center frequency signals by a power loss of about ten percent. The center frequency signals are unaffected. In operation, this can cause the off- center frequency signals to fail to reach the threshold at which stimulated emission takes place. The result is that the laser replicates only the center frequency signals as the laser output.

It was established that backward-scattered wave reflectivity from a signal wave intensity in neodimium-doped and undoped KGd(WO₄)₂-KGW crystals has different dependencies. The interference of electronic and Raman two-photon resonances in neodimium doped KGW crystals are described.

Self-focusing of ruby laser beams is observed in solution for a series of bioengineered polymers. The values obtained for third order nonlinear optical susceptibility (Chi) ⁽³) are compared with observed values by degenerate four wave mixing. It is demonstrated that self- focusing is a sensitive technique for measuring (Chi) ⁽³).