A detailed study of the relaxation self-enhancement (RSE) of the holographic gratings in amorphous films is presented. The changes of the diffraction efficiency have been measured as functions of the aging time and the recording light intensity. The role of the internal mechanical stress of the films in the self-enhancement phenomenon has been discussed. It is shown that the RSE has a vectorial character owing to the uniaxial periodically distributed stress relaxation. A model based on the photoinduced stress relaxation and viscous flow of amorphous film is proposed to explain the experiments qualitatively. It is further shown that the stress-induced optical anisotropy of the films is responsible for the RSE.
© 1997 Optical Society of America