We investigate the highly sensitive surface-induced photorefractive gratings, observed in undoped nematic planar cells for low dc voltage (few volts) and laser intensity (few milliwatts per square centimeter). Forced-light-scattering and two-beam coupling measurements on E7 nematic samples, aligned with rubbed polyvinyl alcohol layers, verify the orientational effect of a space-charge field and the crucial role of the polymer–liquid-crystal interface in the photoinduced processes, through a wavelength-dependent photoelectric activation. The experimental behavior supports the surface-induced photorefractive effect model, according to which light with the proper wavelength locally reduces the interfacial charge density, thus producing a space-charge electric field in the cell.
© 2004 Optical Society of America
(050.1950) Diffraction and gratings : Diffraction gratings
(190.5330) Nonlinear optics : Photorefractive optics
(190.7070) Nonlinear optics : Two-wave mixing
(230.3720) Optical devices : Liquid-crystal devices
(240.6670) Optics at surfaces : Surface photochemistry
Pasquale Pagliusi and Gabriella Cipparrone, "Dynamic grating features for the surface-induced photorefractive effect in undoped nematics," J. Opt. Soc. Am. B 21, 996-1004 (2004)