摘要：

This thesis concerns two topics: the photorefractive ring phase conjugator and the third-order nonlinearities of organic and polymeric materials. For the first topic, I describe the behavior of a ring-type phase conjugator when the time-reversal symmetry in its ring is broken. The nonlinear medium in our phase conjugator was a photorefractive single-domain BaTiO_3 crystal. We found that when a sufficiently large nonreciprocal phase difference, caused by the Faraday effect, was imposed on the ring conjugator, both the frequency and the spatial mode of its output were changed. We observed for the first time in a ring phase conjugator the appearance of higher -order Gaussian modes, and we made a model to explain this effect. For the second topic, we studied the third-order nonlinearities of a group of ladder polymers as well as phthalocyanine dyes. Using picosecond lasers we performed time-resolved degenerate four wave mixing experiments in ladder polymers, polymeric disubstituted ethylaminovinyl -polyquinoxaline (pDEAVPQL) and polymeric disubstituted piperidinovinyl-polyquinoxaline (pDPVPQL). We find that the third-order nonlinear susceptibility tensor components c_{1111} are of the order of 10^{-11} esu. We have made what we believe to be the first observation of the two-photon absorption of phthalocyanine molecules. The wavelength dependence of the two-photon absorption coefficient is consistent with previous theoretical prediction of the existence of two-photon accessible levels in the visible region. This discovery establishes that two-photon absorption is the underlying mechanism of the large, infrared, third -order optical nonlinearity in phthalocyanine dyes. Using a modified Twyman-Green interferometer, we measured both the real and imaginary parts of c_{1111 } of Cr-phthalocyanine dye in the visible and infrared regions. (Copies available exclusively from Micrographics Department, Doheny Library, USC, Los Angeles, CA 90089 -0182.).

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