Theory and applications of molecular and collective nonlinear optical behavior of nematic liquid crystals.

摘要

Two different types of nonlinear effects in nematic liquid crystals have been studied. The first refers to molecular absorption processes in liquid crystals and other similar organic liquids that make them useful for picosecond-nanosecond optical limiting applications. A detailed theoretical study of nonlinear molecular photonic processes accompanying the propagation of short intense laser pulses through a thin organic liquid cell and an organic liquid cored fiber array is presented. A model is proposed to account for the measurements of a recently developed organic liquid, and a comparison with pure two-photon and excited state absorption mechanisms is performed.;The second nonlinear effect is the stimulated orientational scattering (SOS) effect of nematic liquid crystals, arising from the interaction of a laser beam with an elastic medium represented in the collective behavior of the liquid crystal molecules. We have demonstrated efficient all-optical polarization conversion of cw 1.55 mum laser in nematic liquid crystal films. This SOS effect is mediated by two-beam coupling between the incident polarized laser and its orthogonally polarized noise component scattered by the director axis fluctuations. We report a quantitative theory that accounts for severe pump depletion and high-efficiency polarization conversion and demonstrate good agreement with experimental observation. The existence of complex, time-dependent dynamics of the director motion is also revealed and studied.