Electro-Optical properties of photoaligned Liquid Crystal cells prepared with obliquely irradiated Chalcogenide glasses

Abstract We report the effect of oblique irradiation of thin As2S3 chalcogenide glass films on the photoalignment of Nematic liquid crystals and their electro optical properties. After depositing 60 nm As2S3 films on ITO coated substrates, the substrates were irradiated with polarized blue light (436 nm) at angles 0°, 5°, 20° and 48° of the light propagation direction with respect to the substrate plane. Then, the substrates were assembled and filled with the liquid crystal. The device LC-20° exhibits good extinction, and lower threshold voltage when compared to all other devices. The contrast ratio of LC-20° almost double that of the LC-5° and LC-48° devices. The response time increases with the angle, so for LC-20° slightly longer than for LC-5° but shorter than that of LC-48°. It is evident from the observations that the obliquely irradiated cells show good photoalignment and enhanced electro optical properties, although no pretilt is generated due to the oblique irradiation. Therefore, contrary to the photoalignment using photosensitive polymers, chalcogenide glasses have the advantage of providing photoalignment with little sensitivity to the irradiation angle. This fact led us to propose a model for the photoinduced alignment on chalcogenide glasses based on directional structural changes, not related to oriented dipoles generation as in the case of photoalignment with polymers.