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 ? = 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 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.
Functionalized azo-carbazole compounds, when exposed to two interfering polarized coherent laser beams, show efficient mixed amplitude and phase recording ability, frequently accompanied with surface relief grating formation. The aim of the present work is to study the dynamics of grating recording in azo-carbazole compounds using 30 ps train of pulses (532 nm, 1.2 mJ). The build-up of diffraction gratings arising, due to repeated pulses, were probed by a He-Ne laser operating at 632.8 nm by measuring power of a first order of diffraction. The grating period amounted to Λ = 0.76 µm.
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