Liquid Crystal Photonics : Formation of Photoinduced Diffraction Grating of Liquid-Crystalline Polysiloxane

Abstract

Formation of photoinduced diffraction grating within a thin film of a liquid-crystalline polysiloxane with azobenzene in the side chain was investigated. This polymer exhibited a smtectic C phase between 81 and 87℃, and a nematic phase between 87 and 109℃. Moreover, this polymer formed two kinds of solid state at room temperature: an amorphous state and a crystalline state. The crystalline-state sample was prepared by annealing after heating to the mesophase temperature, and the amorphous-state sample was obtained without heat treatment. The alignment of the mesogenic chromophores in the amorphous state is random, while the they form an interdigitated alignment in the crystalline state. The diffraction light was observed in both states by irradiation of two coherent beams. The diffraction efficiency in the crystalline state was smaller than that in the amorphous state. The diffraction efficiency and the rate of formation of the diffraction grating depend on the alignment of the mesogenic chromophores.