Spatial periodicity of photorefractive orientational gratings in dye-doped polymer-liquid crystal composite

Permanent photorefractive orientational gratings induced in dye-doped polymer dispersed liquid crystal show unusually the same refractive index spatial periodicity of the interference light pattern. The quadratic response of the material to the local electric field predicts a grating wave vector twice of the intensity pattern one. In this paper we propose an explanation of this periodicity and experimental results that support our idea.