Thermodiffusive photorefractive phenomena in liquid crystals

We present a mechanism of photorefractivity that does not require photoconductivity for its existence. This mechanism works in light absorbing liquids that contain ions. The light-induced separation of charges takes place due to thermal diffusion. The effect is proportional to the power of absorbed light and can become stronger than conventional diffusive photorefractivity in liquid crystals. The thermodiffusive space charge field may acquire a component along the propagation direction of the light. It is shown that superimposition of thermal and photorefractive modulations of material parameters leads to the possibility of generation of orientational gratings that are spatially resonant with the wave's interference pattern. The results obtained may have large practical importance extending the class of photorefractive materials and offering possibilities of control of photorefractive optical phenomena. [S1063-651X(98)10710-9].