NONLINEAR EXPOSURE DEPENDENCE OF THE HOLOGRAPHIC RECORDING AND RELAXATIONAL STRUCTURAL-CHANGES IN AMORPHOUS AS2S3 FILMS

The exposure dependence of holographic recording has been experimental ly studied in nonannealed amorphous As2S3 films for small exposures le ss than or equal to 1 J/cm(2). The square root of the diffraction effi ciency is found to depend nonlinearly on exposure. This nonlinearity i ncreases when the film thickness is increased and the holographic grat ing period is decreased. No exposure threshold has been found down to exposures of 0.025-0.17 J/cm(2), depending on period. Different reason s for the observed nonlinearity are discussed. Nonlinearity is explain ed in terms of a phenomenological model based on the simultaneous acti on of the photostructural and relaxational structural changes, and thi s model has previously been used to explain the existence of relaxatio nal self-enhancement and the intensify threshold for holographic recor ding in amporphous As2S3 films. The model itself is developed further. (C) 1996 American Institute of Physics.