Photoinduced orientation of azo dye in various polymer matrices

Photoinduced dichroism in various polymers containing the same azo dye has been studied. "Angular hole burning" and molecular reorientation have been identified by analysis of dichroism dynamics at various probe wavelengths. The glass-transition temperature T_g is of major relevance for the reorientation of optically active molecules. For low T_g (below ambient temperature) thermal diffusion impedes anisotropy buildup. For higher T_g the angular distribution induced by the polarized pump beam is frozen. We propose a simple model based on diffusion rates in trans and cis molecules.