Orientational photorefractive properties in polymer-dispersed liquid crystals with different polymer matrixes

ABSTRACT We report orientational photorefractive effects observed in photoconductive liquid crystals (LCs) contained withthree kinds of polymer, i.e., poly(methyl methacrylate) (PMMA), poly(vinyl alcohol) (PVA) and a side-chain liquidcrystalline polymer (SLCP1). The morphology of the photorefractive composites depended on the kind of polymer strongly.In both PMMA and PVA cases, LC and polymer were phase-separated and the composites showed memory effects. InSLCP1 case, the phase-separation in the composite dose not occur and the high resolution could be achieved. In this case,the photorefractive Bragg gratIngs were generated and a high two-beam coupling gain coefficient (75 cm') with a lowapplied field of 4 V/pm was observed.Keywords: polymer dispersed liquid crystal, photorefractive effect, hologram, photoconductive effect,nonlInear optics, two-wave mixing, degenerate four wave mixing. 1. INTRODUCTION Photorefractive materials have attracted a lot of attention both from the point of view of fundamental science andpractical applications such as a real-time hologram, a high-density hologram record medium, and a medium of the phaseconjugation gh2 Since the photorefractive studies were extended into organic materials in 1990,