Optical phase conjugators exhibiting extremely high gains and low thresholds have been developed over the last decade by researchers using Brillouin-enhanced four wave mixing (BEFWM). This phenomenon, based upon the interaction between light and acoustic waves in a nonlinear medium, is still not fully characterized theoretically or experimentally. In particular, the frequency relationships among the four interacting light waves plays a crucial role. In this paper, experiments investigating the spectral nature of BEFWM using two tunable single mode YAG lasers are described.

The Brillouin-enhanced four-wave mixing (BEFWM) technique for phase conjugation in high-power laser systems is presented. The technique represents a form of nearly degenerate four-wave mixing in which the four beams are coupled acoustically through Brillouin nonlinearity. Emphasis is placed on the case of the Brillouin geometry where the second pump beam is downshifted by the acoustic frequency from the first pump. A 1D steady-state model has been developed which takes into account the limitation of the reflectivity of the BEFWM process due to the presence of a small component of the second pump beam with the same polarization as the first pump beam. In addition, 3D wave optics code have been developed for calculating the conjugation fidelity under less than ideal conditions such as misalignment of the pump beams, the two pump beams not being perfect conjugates of each other, etc.

A theoretical/experimental study of beam coupling by stimulated Brillouin scattering (SBS) is reported. The theoretical work examines the build-up, transient through steady-state, of two SBS beams excited by partially overlapped pump-beams and is directed toward understanding how two output SBS beams are coupled together. Experimental work reports measurements of the mutual coherence of the two Stokes beams as a function of the relative intensity, overlap and polarizations of the pump beams. The experimental work verifies the key theoretical result that four-wave mixing is responsible for beam coupling and for the establishment of the mutual coherence of the two Stokes beams.

Photorefractive two-wave mixing was examined in the context of optical image amplification for diffusion-driven crystals at three wavelengths. Gain, beam fanning, and energy distribution at the image plane were studied in poled doped samples of KNbO₃, BaTiO₃, and SBN. Response were characterized at 514.5 nm, 632 nm, and 823 nm. To study the response at 823 nm, a mode-stabilized laser diode was used. To achieve stable optical image amplification in a continuous wave regime, low light levels were required for BaTiO₃ at 514.5 nm. KNbO₃ was a viable coupler at 514.5 nm at milliwatt power levels. Data indicates that SBN is a suitable coupler in the green only at extremely low power levels (microwatts). All three crystals exhibited gains in the near-infrared

This paper reports an experimental study of coherent coupling of lasers using a BaTiO₃ photorefractive ring oscillator with a multiplexing holographic grating plate for fan-in/fan-out purposes. Phase locking between or among lasers was observed. However, the slow response speed (with about 10 milliwatts optical power at 632.8 nm) of the photorefractive process and the high sensitivity of the BaTiO₃ ring oscillator resulted in transverse mode instability and oscillation power fluctuation, which limits the phase locking phenomenon in this system on a temporary basis only.

The imaging properties of optical arrays are analyzed in this paper based on unparaxial ray theory. A high-order imaging theory is also discussed. The theory includes not only paraxial theory, but can be shown in regular matrices from which we consider a surface optical array that can achieve phase conjugation. Experiments presented in this paper prove the theoretical analyses.

Photoemission from quantum wells, inversion layers, quantum well wires, and quantum dots of nonlinear optical materials has been studied using n-CdGeAs₂ as an example. Photoemission was formulated by deducing the dispersion law within the framework of the k-p formalism taking into account all types of anisotropies of the energy band parameters. Photoemission is found to increase with incident photon energy in a ladderlike manner and to exhibit an oscillatory dependence on changing film thickness, surface fields at both high and weak electric field limits, and the carrier density. It is concluded that the numerical values of the photoemission are the greatest in quantum dots and the smallest in bulk specimens.

The third order optical nonlinearity of quantum confined CuCl-doped borosilicate glass caused by saturation of the excitonic absorption is reported. Induced index changes were estimated using the Kramers-Kronig analysis of the bleaching data. The nonlinear refractive index is reported as a function of particle radius and is found to increase with increasing radius over the range 22 A to 34 A.

Optical nonlinearities in quantum confined CdSe microcrystallites are investigated by degenerate four-wave mixing at various wavelengths in the vicinity of the absorption edge. The experimental results show a resonantly enhanced degenerate four-wave mixing signal for the smallest microcrystallite sample, indicating electron-hole quantization.

The first demonstration of mid-infrared generation in KNbO₃ by frequency downconversion from a 1.064-micron laser is reported. A 35 percent photon conversion efficiency is achieved for generation of light at 3.4 microns. The phase-matching curve and temperature sensitivity for the process is presented, and the temperature acceptance is measured to be greater than 6.7 cm-°C.

A ps automatic tuning parametric Nd:YAG laser based on a single pair of MgO.LiNbO₃ crystals is described. Energy and power efficiencies obtained are 5.4 and 8.6 percent, respectively. In a wide wavelength range, a single pulse of less than 30 ps is observed with bandwidths of approximately 1 nm and a peak power over 1 MW.

By mixing the fourth harmonic and stimulated Raman scattering of Nd:YAG mode-locked laser (1.06 micrometers ), the shortest ultraviolet coherent light in LBO crystal has been generated.

The unique features of photorefractive compound semiconductors are presented. The advantages of this class of nonlinear optical materials for optical processing are illustrated with examples using GaAs and InP. The difference between GaAs and InP in the laser power density requirement is discussed.

The noise characteristics and the low-light-level imaging capabilities of a stimulated Raman amplifier have been investigated. Stokes beams carrying spatial structure have been amplified using a collimated pump with a Fresnel number of 17. Both direct imaging of the Stokes signal and Fourier transform imaging of the Stokes signal through the Raman amplifier were used. Evidence of interference between the quantum noise field and the seed-Stokes field is present at the lowest seeding levels.

This paper presents an examination of power dissipation in a nonlinear optical medium during the coherent transfer of energy from a pump to a signal beam, and quantitatively relates this dissipation (through the fluctuation-dissipation theorem) to the spectrum of thermal fluctuations that give rise to light-scattering noise. Calculations are presented for two-wave mixing in an artificial Kerr media using a powerful stochastic model for computer simulation of amplitude, phase, and intensity fluctuations due to light-scattering noise.

Coherent Stokes pulses are generated under amplification of the spontaneous Stokes noise radiation appearing in intense laser pulses Raman scattering. Radiation intensity selflimitation under the selffocusing in Raman media is corresponded to ejection of excess power to divergent coherent Stokes components.

A method for the self-action analysis of wide-spectral extremely short light pulses (ESLP) in fibers is presented. The method takes into account the dispersion of linear and cubic nonlinear susceptibilities in the transparency range of the media. The density matrix formalism was used to obtain material equations describing the ESLP self-action in fused silica. Light pulses with a duration about several light-wave oscillations are shown to be compressed in the nonlinear medium.

This paper investigates the quantum oscillations of the Raman gain in non-parabolic semiconductors under strong magnetic quantization, taking A₃^II B₂^V compounds as examples of nonlinear optical materials. The magneto-dispersion law was formulated in the said material within the framework of k. p formalism taking all types of anisotropies of the energy spectrum. The expression for the Raman gain for the said compound was derived, taking Cd₃P₂ as an example by including spin and broadening effects. It is found that the Raman gain increases with increasing electron concentration and oscillates with magnetic fields. The numerical values of the gain are greatest for the proposed dispersion relation of A₃^II B₂^V type of nonlinear optical materials as compared to wide gap model and the theoretical analysis is in agreement with the experimental observations as reported elsewhere. In addition, the corresponding results for three-band Kane model, two-band Kane model, and parabolic energy bands also have been formulated.

A newly developed expansion technique is used on the density operator in quantum optics. It is shown how an expectation value of order n can be written in terms of the (n-2) order. From this, a simple formulation of high order nonlinear susceptibilities is presented and some examples are given.

Polarization-resolved coherent beam combination via nondegenerate two-wave mixing have been observed in water-glycerol suspensions of shaped polytetrafluoroethylene microparticles. Experiments detect coherent energy transfer arising from two different types of moving index gratings: translational and orientational. Additionally, the dependence of the two-wave mixing gain coefficient on the frequency-difference of the beams, pump intensity, and microparticle volume fraction was measured and found to be in accord with theory. Finally, beam combination was also achieved using degenerate laser beams and moving the suspension relative to the laser interference pattern.

Second order nonlinear optical (NLO) polymers containing NLO moieties with large optical nonlinearities and a cross-linkable unit have been synthesized using difunctionalized disperse red dye. The enhanced second order NLO coefficients, X exp (2) of 250 pm/v for the first polymer and 500 pm/v for the second, were obtained at 532 nm using the corona poling method. The introduction of flexible chains into the polymer backbone is found to cause a decrease in glass transition temperature and, hence, a decrease in the stability of the second-order NLO effects.

Nonlinear optics (NLO) is increasingly important for a variety of military and commercial needs ranging from new types of laser weapons to fiber optic communications networks, to optical computing applications. Rapid advances in optical phase conjugation, optical switching, and logic have demonstrated the enormous potential for practical applications with concurrent fast-paced materials development. The research has established that polyimides potentially have the excellent intrinsic properties and tailorability to meet the requirements of a wide range of nonlinear optical devices. The research described in this manuscript is a multidisciplinary effort to target key applications and material and processing requirements for these polymers. It discusses the synthesis, characterization, and processing of the nonlinear optical properties of polyimides which have been tailored for nonlinear optical activity.

A nonlinear interferometer with phase conjugate mirrors was constructed to measure relative magnitude and phase of third order susceptibilities. This SWR-interferometer measured the third order susceptibilities of solutions of diphenylpolyenes (n = 1-4) in dichloroethane at 532 nm. The second hyperpolarizabilities derived from these susceptibilities are compared with the values obtained from electric field induced second harmonic generation at 1064 nm. The temporal behavior of the phase conjugated signals in the SWR-interferometer is analyzed for parallel and perpendicular polarization of the probe vs. pump laser pulses (5 nsec, 5 mJ). The role of this temporal behavior on the operation of the interferometer is assessed.

This paper studies the effect of a parallel magnetic field on the gate capacitance of MOS field- effect devices of tetragonal type of non-linear optical materials, taking n-Cd₃As₂ as an example. The expressions of the gate capacitances were derived for the present system for both the weak and the strong electric field-limits respectively. It was found, on the basis of newly derived generalized two-dimensional electron energy spectra by incorporating anisotropic crystal potential to the Hamiltonian together with the anisotropies of the effective electron mass and the spin-orbit splitting of the valence band within the domain of k. p theory, for both the limits, that the gate capacitances increases with increasing surface electric fields in an oscillatory manner. The gate capacitances also exhibit monotonous variations with increasing magnetic fields with different numerical values for both weak and strong field limits respectively. The theoretical results are in agreement with the experimental observation as reported elsewhere. In addition, the corresponding results of the gate capacitances in the absence of parallel magnetic field on the basis of our proposed dispersion law, three-band Kane model and two-band Kane model of MOS field-effect devices of nonlinear optical materials have been obtained.

A series of theoretical and experimental studies shows that the 10.6-micron laser frequency stabilization system of double photoelectric circuits with NH2D Stark Cell has good characteristics. In this system, the frequency stability is measured with heterodyne technique, and computer realtime data processing by means of the Allan Variance calculation. The measurement results of long-term and short-term frequency stability are introduced for different sampling time.

In this paper we consider the experimental results of investigations of the nonlinear optical system with a purely optical two-dimensional feedback circuit. The possibility of effective compensation in the system of static and dynamic phase distortions, which were theoretically analyzed, have been observed experimentally. New type of optical novelty filter based on adaptive suppression of phase images is elaborated.