Relaxation kinetics of photoinduced surface relief grating on azopolymer films

The relaxation kinetics of the photoinduced surface relief grating (SRG) formed on an azopolymer film after stopping laser beam writing has been systematically investigated. In addition to a photoinduced increase of the diffraction efficiency in the SRG, an anomalous further enhancement of the efficiency was observed even without light irradiation, after the recording light beam was switched off. This anomalous relaxation process consists of two components with short and long relaxation times, and strongly depends on the temperature and polarization of the probe beam used for the diffraction measurement. At lower temperatures the anomalous growth is more effective and the fast component is dominant. From the results of the polarization dependence of the diffraction efficiency and optical absorption, it has been manifested that the fast component of the relaxation originates from the cis-trans thermal isomerization of azobenzene in the side chain. The origin of the slow decay is also discussed in terms of the order parameter change of the azomolecules caused by the reorientational relaxation. (C) 2002 American Institute of Physics.