Red light induced holographic storage in an azobenzene polymethacrylate at room temperature

Holographic diffraction gratings have been induced at room temperature (RT) using red light (633 nm), in a liquid crystalline side chain cyano-azobenzene polymethacrylate polymer. Stable gratings have been obtained under simultaneous irradiation with the interference pattern created with two coherent linearly polarized red light beams and UV (around 350 nm) unpolarized light. The main contributions to the diffraction efficiency can come from the photoinduced orientation of the azo units and perhaps from changes in the light transmitted through the regions of the film that have been illuminated with both red and UV light and those only illuminated with the UV light. Higher efficiency is achieved if the red light polarization is perpendicular to the grating vector than if it is parallel to that vector. Stable gratings have also been induced with either sequential or simultaneous irradiation with blue (488 nm) linearly polarized light and the red interference pattern. The contributions to the efficiency can have the same origin as under UV and red light illumination. The highest efficiency is achieved under simultaneous illumination with both blue and red light polarizations perpendicular to the grating vector.