Orientational photorefractivity and optical response of layer-structured nematic liquid crystal cells doped with fullerene

Abstract

The optical responses and orientational photorefractivities of nematic liquid crystal cells doped with fullerene were investigated with layered structure. The spatial modulation of the refractive index due to charge redistribution would be applied in high-density optical data storage, optical image processing, as was the orientational photorefractivities of nematic liquid crystals for conjugated mirror, and real-time holography. The photorefractive effect in nematic liquid crystals attracts much interest because of their extremely large change of refractive index that can be induced in them by laser or applied voltage. The mechanism of generating photorefractive effect using liquid crystals is slightly more complicated, different from that of other photorefractive materials, and is attributed to the refractive index change due to the reorientation of directors of liquid crystals from an internal space-charge field. The method to distinguish the photorefractive effect from other types of gratings which may occur in photorefractive materials is two-beam coupling measurement which shows asymmetric energy exchange. In nematic liquid crystals, the Raman-Nath diffraction regime must be satisfied to obtain high photorefractive efficiency. Diffraction efficiency can be obtained by measuring the first-order Raman-Nath diffracted beam. In order to prepare a hybrid-structured photorefractive cell, the photo-alignment study has been performed ahead. With the result, we could prepare highly transmitted hybrid-structured photorefractive cell and obtain reasonably high photorefractive effects. We could find that the reorientation of liquid crystals onto photoconduction layer would govern the whole photorefractivity in layer-structured liquid crystal system. When nematic liquid crystals are injected at a nematic phase, the better cell texture can be obtained due to flow-induced orientation effect. Sample with this method showed much higher photorefractive effects than that inj...