Stimulated orientational and thermal scatterings and self-starting optical phase conjugation with nematic liquid crystals

A quantitative theory and experimental results on self-starting optical phase conjugation, using stimulated orientational and thermal scattering in nematic liquid crystal films, are presented. The coupled wave-material equations for the laser-induced refractive index changes, grating formation, and coherent wave mixing effects are developed. Analytical solutions are obtained for the case of negligible pump depletion, and numerical solutions for various input and generated signals, taking losses into account, are obtained. Experimentally, we demonstrate the feasibility of realizing these stimulated scattering and phase conjugation processes in thin (200 μm) nematic liquid crystal with a milliwatt-power cw laser. Theoretical estimates for various gain constants and threshold intensities, and their dependence on various physical parameters, are found to be in good agreement with experimental observations.