Observation of high gain in a liquid-crystal panel with photoconducting polymeric layers

A novel, to our knowledge, Liquid-crystal panel suitable for real-time holographic purposes has been prepared. A nematic Liquid-crystal layer sandwiched between photoconducting polymeric layers, when exposed to a sinusoidal light-intensity pattern, shows efficient formation of refractive-index gratings. The unique feature of the presented panel is its ability to switch energy from beam to beam in a manner similar to the charge-diffusion-controlled photorefractive effect. In a two-wave-mixing experiment multiple orders of diffraction are present, and a very high two-beam coupling-gain ratio (2.5) and a net exponential gain coefficient of Gamma = 931 cm(-1) have been measured. This gain was achieved in samples biased by a de external electric field and tilted with respect to the beam-incidence bisector at 45 degrees. The time constants for grating formation and erasure in the studied system are functions of the applied voltage and can be made as short as a few milliseconds under favorable conditions. The mechanism of beam coupling is linked with an electric-field-driven reorientation of the nematic director as a result of a spatially modulated space-charge field created by light in a photoconducting poly(3-octyl)thiophene polymeric layer. (C) 1998 Optical Society of America.