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 laye r sandwiched between photoconducting polymeric layers, when exposed to a sinusoidal light-intensity pattern, shows efficient formation of re fractive-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 ve ry 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 ac hieved in samples biased by a de external electric field and tilted wi th respect to the beam-incidence bisector at 45 degrees. The time cons tants for grating formation and erasure in the studied system are func tions of the applied voltage and can be made as short as a few millise conds under favorable conditions. The mechanism of beam coupling is li nked with an electric-field-driven reorientation of the nematic direct or 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.