Thermal grating-mediated wave mixing and beam amplification in nematic liquid crystal thin films

A model is presented of thermal grating-mediated wave mixing and amplification. The model includes a strong pump beam, a weak probe beam, and a first-order diffracted beam. The coupled Maxwell's wave equations and the thermal diffusion equation are solved using a self-consistent formalism. The influence of various input beam parameters (the pump to probe beam intensity ratio, beam intensities, crossing angle, wavelength) and sample parameters (the thermal nonlinear coefficient, thermal conductivity, sample thickness) on the wave mixing effects is considered. Some recently observed infrared beam amplification effects have been qualitatively described by the theory of the optimum configuration for signal (probe) beam amplification with nematic liquid crystals. The results are important for optical phase conjugation and self-oscillation processes involving infrared lasers, and demonstrate the particular usefulness of liquid crystals for these applications.