Photo-aligned and photo-conductive polymer layers for photorefractive liquid crystal cells of high transmittance

The optical performance of photorefractive cells of liquid crystals strongly depends on the alignment of liquid crystals stabilized by surface states. Two photo-aligned polymer layers with relatively weak anchoring energy were investigated by FT-IR and UV/VIS spectroscopies. The cells without alignment layers showed significant scatterings due to random switching under an applied field. The cells with photo-alignment layers showed the high transmittance because of the high orientation order, but a little decrease in gain coefficient and diffraction efficiency because of the decrease in trap sites. Therefore, it is concluded that the reorientation of liquid crystals onto photo-conduction layer would govern the photorefractivity in two-beam coupling experiments. (C) 2002 Elsevier Science B.V. All rights reserved.