Transient multiwave mixing and diffraction with nonsinusoidal intensity-dependent index grating in a nonlinear medium

We study the effects of an intensity dependence in the nonlinear index change coefficient on transient and steady-state optical wave mixing and self-diffractions, using the temperature-dependent thermal index change of a nematic liquid crystal as a model material. We show that the nonsinusoidal index grating created by a sinusoidal optical intensity grating has significant influence on the phases and amplitudes of the multiwave mixing processes. Experimental results on the intensity distribution of the multiorder diffractions in a nematic liquid-crystal film near the phase transition temperature are also presented to illustrate the basic effects.