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 Γ = 931 cm-1 have been measured. This gain was achieved in samples biased by a dc external electric field and tilted with respect to the beam-incidence bisector at 45°. 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.
© 1998 Optical Society of America
(050.0050) Diffraction and gratings : Diffraction and gratings
(160.3710) Materials : Liquid crystals
(160.5320) Materials : Photorefractive materials
(190.7070) Nonlinear optics : Two-wave mixing
(230.3720) Optical devices : Liquid-crystal devices
Stanislaw Bartkiewicz, Andrzej Miniewicz, Franņois Kajzar, and Malgorzata Zagórska, "Observation of High Gain in a Liquid-Crystal Panel with Photoconducting Polymeric Layers," Appl. Opt. 37, 6871-6877 (1998)