Photorefractive liquid crystals

A review of the field of photorefractive liquid crystals is presented. The first reports of photorefractive liquid crystals occurred in 1994, and the performance of these materials has dramatically improved since that time. L iquid crystalline materials have proven to be highly versatile, showing pho torefractive character under a wide range of conditions. For example, new c omposites based on high-molar-mass liquid crystals are now capable of formi ng volume (Bragg) gratings with high photorefractive gain coefficients of > 600 cm(-1). Formation times for photorefractive Bragg gratings of 15 ms wi th applied fields of only 0.1 V/mum have been reported. Low-molar-mass liqu id crystals continue to be developed and show their largest photorefractive character in the thin (Raman-Nath) grating regime. Composites of nonmesoge nic polymers and liquid crystals are also discussed. The experiments and th eoretical work that have been used to characterize these materials are revi ewed.