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

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 hidden gratings and transient gratings formed in the presence of a dc electric field and two coherent pump beams. Our experiments suggest that these persistent hidden gratings are...