Temporal Dependences of Optical Nonlinearities of Nematic Liquid Crystals and the Unusual Polarization Dependence of Self Diffraction in 4-4′-Bis(Heptyloxy) Azoxybenzene

We present a quantitative analysis of the temporal dependences of optical nonlinearities of nematic liquid crystals induced by laser of pulse duration from nanosecond to milliseconds (or longer). The nonlinear mechanisms we have considered include thermal, density and reorientational effects. This analysis provides a useful guideline for using such nonlinear optical responses in practical devices. We also report the preliminary observation of an unusual polarization dependence in a particular nematic liquid crystal.