Sheremet N. Light-induce anchoring of nematic liquid crystals with chalcogenide glass surface

Basic properties of light-induced anchoring of a liquid crystal (LC) with a chalcogenide glass surface were studied. It has been demonstrated that the increase of the dose leads to change orientation of LC direcror on chalcogenide glass surface. This is a result of two different mechanisms of light-induced anchoring of LC with the chalcogenide surface. The first mechanism is related to the light-induced anisotropy of the chalcogenide surface and leads to orientation of the LC parallel to the polarization of the incident light. The second mechanism is associated with a polarization sensitive desorption of LC molecules from the chalcogenide glass surface and producing an easy orientation axis is perpendicular to the polarization of the light. The desorption of LC molecules occurs as a result the transfer of energy from the dichroic units of chalcogenide film after the light absorption to the adsorbed layer of LC molecules on the chalcogenide surface. The competition between these mechanisms leads to the observed change of the direction of the easy axis with the exposure. The photoalignment effect of LC on chalcogenide glass surface is used for recording of the polarization gratings in cell. Application of ac-electric field allows control the diffraction efficiency of the hologram due to a phase grating that is formed in addition to the polarization grating and this allows increasing the grating efficiency. The patterns appeared upon irradiation of the tested surface through the LC layer with laser gauss beam. It was shown that the effect is due to a spatial modulation of the polarization state of light in the plane of the chalcogenide film. The oscillating changes of the light polarisation produce the light-induced easy orientation axis with the oscillating changes of the anchoring energy. It causes the spatial modulation of the director on the chalcogenide surface and the formation of the concentric ring twist structures in the cell.