A new family of selective four-wave mixing methods, based on the establishment of vibrational nonlinear polarizations with multiple resonances, is proposed. This family includes double-infrared resonances, vibrationally enhanced Raman resonance, and vibrationally enhanced two-photon resonance. These methods are related to traditional Raman and infrared spectroscopy, but the methods are shown to have the capabilities for component and conformer selectivity, line-narrowing of inhomogeneously broadened vibrational transitions, and mode selection. The theoretical foundations for the methods are developed and directed to possible applications.

Pb,La)(Zr,Ti)O 3 (PLZT) is one of the best candidates in terms of high-speed, low-voltage, and low-power consumption optical switching due to its efficient voltage-induced index change. We have established a solid-phase epitaxy to grow low-loss PLZT thin film waveguides. PLZT waveguides with PLZT buffer layers are grown on Nb-doped semiconductive SrTiO 3 substrates for the effective overlap integral of the optical field and the electric field. Efficient switching of light coupled in the waveguides is achieved by applying voltage between the top electrodes and the substrates to induce the excellent electro-optic properties of PLZT waveguides including low-voltage and polarization independent index change. 1xN optical switching devices and subsystems are demonstrated using the PLZT waveguide switch elements showing low-voltage drive and less than 10 ns response characteristics.

We describe a new nonlinear, nonparametric process that provides a direct measure of vibrational enhancement in four wave mixing. This process has 14 coherent pathways that create the final coherence. In the limit of no pure dephasing and a single vibrational resonance, the 14 pathways combine into a single process that is vibrationally enhanced. The frequency and concentration dependence expected for this process matches that observed in experiments with the methyl- and methylene C–H stretch vibrations in hexane samples. The third-order nonlinear susceptibility for the C–H vibrations was measured by the interferometric method of Levenson and Bloembergen. The vibrational nonlinearity was observed as a difference between the nonresonant electronic contributions and the contribution that depended on resonance with the vibrational absorption transition. The measurements show that the vibrational enhancement is 50 times larger than the nonresonant electronic contribution and it shows that spectroscopic methods based on resonant nuclear nonlinear polarizations are observable above the electronic nonlinear polarization background.

In order to determine the feasibility for a new family of nonlinear four-wave-mixing methods based on resonantly enhanced nuclear polarizations, the enhancement of a singly vibrationally resonant, nondegenerate, nonparametric process is measured using an interferometric method. The measurement shows that the resonant nuclear x ͑3͒ polarization is much larger than the nonresonant electronic x ͑3͒ polarization for typical infrared transitions and new spectroscopic methods based on vibrational coherences are feasible. [S0031-9007(97)

Vibrationally enhanced infrared and vibrationally enhanced Raman four-wave mixing spectroscopy are experimentally explored with the use of several model systems. Studies involving a mixture of chlorobenzene, dichlorobenzene, and deuterobenzene were performed to see whether a simultaneous resonance of a combination band could enhance the Raman ring breathing mode. The results show strong interference effects that may be responsible for a suppression of the Raman resonances. Studies were also carried out in systems of chloroform/deuterobenzene and hexane/deuterobenzene. The latter samples showed intensity increases and line-shape changes that are consistent with vibrational enhancement. The discovery of these enhancements form the basis for developing infrared four-wave mixing as a method for extracting new information about molecular vibrations.

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Waveguide linear-dichroism measurements were used in determining the molecular orientation of N-(sulfopropyl)-4-(p-dioctylaminostyryl) pyridinium in Langmuir-Blodgett monolayers upon 150-microm-thick glass (Ti:Zn) substrates in real time. Acquisition of complete spatial-decay curves in t - 1 s with P(laser) = 100 microW was made possible by combining propagation in integrated-optical structures with direct imaging of monolayer or glass fluorescence onto the active area of a charge-coupled device camera. Multichannel detection permitted measurement of optical waveguide loss coefficients and ultimately of molecular orientations in approximately 10(-3) of the amount of time required by previous methodology. The effects of sample preparation and materials processing on the accuracy and precision of dichroic ratios are discussed. Observed dichroic ratios for a hemicyanine dye revealed no measurable change in the orientation of the electronic transition-dipole moment when Langmuir-Blodgett films were deposited at different surface pressures. These results are in good agreement with the results from singly resonant second-harmonic generation experiments.