Hidden surface photorefractive gratings in a nematic-liquid crystal cell in the absence of a deposited alignment layer

摘要

We have carried out studies of photoinduced diffraction in a homeotropically aligned liquid-crystal cell on indium tin oxide with no alignment layer deposited between the electrodes and the liquid crystal. We have observed diffractive components from both persistent bidden gratings and transient gratings formed in the presence of a de electric field and two coherent pump beams. Our experiments suggest that these persistent hidden gratings are due to a light-induced modulation of the surface charge of adsorbed species that is hidden by diffusion of bulk charge to screen the surface charge in the absence of an applied field. The applied field removes the screening charge, revealing the hidden surface-bound charge modulation. This persistent hidden grating can be manipulated by the application of light and/or a dc electric field. Dynamics and other properties are studied and described. (c) 2006 Optical Society of America.