Photorefractive effect has a variety of applications, such as high-density optical data storage, optical image processing, phase conjugated mirrors, dynamic holography and optical computing.
It is important to understand two-beam coupling or asymmetric energy exchange behavior to differentiate photorefractive effect from other local effects. Numerical calculaton of wave mixing theory was performed to understand two-wave mixing phenomena in depth using Runge-Kutta method. The behavior of two-wave mixing was examined as functions of incident beam power ratio, gain coefficient, absorption coefficient, and travel distance in codirectional and contra directional cases.
The transport and trapping of photocharges in photorefractive liquid crystals sandwiched with photoconductive polymer layers was investigated systematically. The transport process of the photocharges is explained in terms of current paths that are formed along the bright sites of the interference pattern. It was shown that charge trapping occurs predominantly in the photoconductive poly(N-vinylcarbazole) layers, not in the insulating poly(vinyl alcohol) layers, contrary to a previous report. Energy transfer and gain coefficient up to $310cm^{-1}$ were obtained in the liquid crystal systems.
Energy exchange between two writing beams in two-wave mixing experiments was observed in polymer systems containing hemicyanine dye. It was found that photobleaching of hemicyanine dyes contributed to forming refractive index gratings in the polymer samples. It was observed that interference pattern on the polymers containing hemicyanine dye and photopolymers slowly shifted with respect to the refractive index grating and long term oscillation of energy exchange took place. The short term competing oscillations of energy transfer in the photopolymers may be attributed to collective pressure-driven mass transport.
