Liquid crystal orientation by holographic phase gratings recorded on photosensitive Langmuir-Blodgett films

Abstract

Holographic gratings were recorded on photosensitive Langmuir-Blodgett films characterized by UV spectroscopy, birefringence measurements and atomic force microscopy. Different polarizations of Ar laser writing beams create particular patterns of chromophore orientation in the diffraction spots. The gratings were shown to orient a nematic liquid crystal with the director parallel to the axes of the chromophores predetermined by film irradiation. In the case of the sp grating (recorded with laser beams polarized perpendicular to each other), two equivalent easy directions for the liquid crystal orientations at 90degree with respect to each other were observed; that is a quasi-bistable anchoring interface had been prepared. Measurements of the pretilt angles theta1s and anchoring energy Ws of 5CB on different holographic gratings show that this orientation technique is very promising for display technology.