Multiple novel effects of high intensity light propagation in highly nonlinear media were investigated in this Dissertation. The first deals with the nonlinear properties of one-dimensional organic polymers, specifically polydiacetylenes. The second deals with the properties of multi-quadratic-soliton generation when the input is several times the single soliton threshold.; Polydiacetylenes are organic polymers with a large nonlinear response due to strong electron delocalization along the direction of polymerization. The Kerr nonlinearity, and the two, three and four photon absorption coefficients of the polydiacetylene PTS (polymer poly (bis para-toluene sulfonate) of 2,4-hexadyine-1,6 diol) were measured over the range from 800 nm to 2200 nm. It was identified theoretically that an initially puzzling thickness dependence of the nonlinear absorption was due to the complex beam evolution in polydiacetylenes for which a strong interplay between Kerr self-focusing and higher order multiphoton absorption occurs. The data for higher order nonlinear absorption revealed for the first time a rare phenomenon in nonlinear optics, namely three photon enhanced four photon absorption. In addition, a comparison of the dispersion in the two photon absorption coefficient in dilute 3BCMU (polymer poly [4,6-dodecadiyn-1,10-diol-bis(n-butoxycarbonylmethylurethane)]) strands with that of single crystal PTS showed that single molecule theories should be useful for predicting polydiacetylene nonlinearities in the solid state.; The second half of the work examined spatial quadratic soliton excitation with a fundamental beam at intensities multiple times the single soliton threshold. The spatial anisotropy in the diffraction was found to be responsible for multiple soliton generation in quadratic crystals. Multiple soliton excitation was characterized numerically and experimentally and the properties of anisotropic solitons were investigated. An all-optical switching scheme was proposed via computer simulations and was tested experimentally.
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