Molecular Crystals and Liquid Crystals

Photoinduced Surface Alignment: The Role of Liquid-Crystalline Order

Abstract:

The optical control of surface alignment was investigated, using azo-dye doped polyimide films as photosensitive material. The kinetics of the realignment of the easy axis was measured in isotropic, nematic and smectic A phases. It is demonstrated that the light-induced realignment of the dye molecules at the polymer-liquid crystal interface is strongly influenced by the presence of the liquid-crystalline order. A simple model is presented, which accounts qualitatively for the experimental observations.

LC Alignment Controlled by Photoordering and Photorefraction in a Command Substrate

Molecular Crystals and Liquid Crystals

Absorptive Dynamic Diffraction Gratings in a Dye-Doped Nematic Liquid Crystal

Abstract:

Dynamic diffraction grating formation by crossed pump beams with wavelength 514 nm in a mixture of 5CB and azodye R4 was investigated by a probe beam with wavelength 633 nm. The dependence of the diffraction efficiency on the pump and probe polarization is consistent with the dye bleaching and corresponding buildup of the cis species as the main mechanism for the optical grating formation. Diffraction at 633 nm is absorptive and is caused by the periodic distribution of the cis species which absorbs in the red. This observations are in quantitative agreement with simutaneous measurements of absorption at 514 nm and at 633 nm. A rate equation model of the grating formation is presented.

LC Alignment Controlled by Photoordering and Photorefraction in a Command Substrate