Complex structures of surface relief induced by holographic recording in azo-dye-doped elastomer thin films

We report observations of unusual and complex structures recorded on the surface of azo-dye-doped elastomer thin films after irradiation with different interference light patterns. Periodic structures with a variety of topography are inscribed through holographic recording by both intensity light patterns and polarization patterns. Diffraction efficiency of the recorded gratings has been measured. Atomic force microscope measurements confirm the presence of complex structures. For some pattern configurations modulated profiles in two directions (both parallel and perpendicular to the grating wavevector) are observed. The depth and periodicity of the structures are investigated. Analyses of film surfaces after irradiation with a single uniform polarized light beam make evidence of photoinduced micrometer-sized structures depending on the film thickness. Only for linearly polarized light are ordered structures produced; stripes oriented perpendicular to the polarization direction are observed. This last observation suggests that the formation of complex structures by holographic recording can be attributed to the combination of a spontaneous patterning, ensuing from light-induced surface instability, and the large material displacement usually observed on surface relief grating formation in polymer-dye systems, with both intensity and polarization light patterns.