Polarized laser induced holographic surface relief gratings on polymer films

Large-amplitude holographic surface relief gratings on azobenzene-containing polymer films were optically induced without any subsequent processing steps. The surface relief structures were observed upon exposure to an interference pattern of polarized Ar+ laser beams. The surface relief structures were investigated using atomic force microscopy. A very regularly spaced surface grating with a surface modulation depth of over 1000 Angstrom was obtained. The gratings were stable at ambient conditions, and the samples were reusable after erasing the gratings by heating the film above the glass transition temperature. The orientation of the azobenzene groups was induced first and followed by the surface deformation process. The polarization of the writing beam had a significant effect on the surface modulation process. The relation between the surface change and optically induced orientation of the azobenzene groups is discussed. Thermal effects were also investigated by studying the dependence of the writing intensity and grating spacing on the grating formation process.