Dynamics and uniformity of reorientation in liquid crystal cells with PVK alignment layers

We present experimental results on dynamics of Freedericksz transition in liquid crystal cells with alignment layers made of poly(N-vinyl carbazole). DC electric field causes the build-up of, unusually strong, surface charge layers on a liquid crystal-polymer interface that screen liquid crystals from the external field. The process of surface charge build-up and discharge in illuminated areas takes place due to low dark conductivity and high photoconductivity of poly(N-vinyl carbazole), rather than due to its photorefractive nature. If the illuminating beam has a Gaussian profile, reorientation starts from a very small volume, with a clear disclination line in the reorientation spot

Dye-doped Photorefractive Liquid Crystals for Dynamic and Storage Holographic Grating Formation and Spatial Light Modulation

The basic mechanisms of photo-induced space charge field formation, director axis re-orientation, and refractive index changes in fullerene C60- and dye-doped nematic liquid crystals films are presented. In particular, in aligned methyl-red-doped nematic liquid crystal film, we observe a nonlinear index change coefficient as high as 10 cm2/W, associated with purely optically induced liquid crystal director axis re-orientation. Experimental observations of dynamic and high-resolution storage holographic grating formation, two beam coupling with gain of nearly 3000 cm-1, optical limiting action at nanowatt cw laser power, and incoherent-coherent image conversion at μW/cm2 light intensity level are discussed