Optical dephasing in doped polymers and the soft potential model: analysis of photon echo in doped PMMA

The approach for description of the optical dephasing in doped amorphous solids in the framework of the soft-potential model (SPM) was developed. A procedure for calculation of the homogeneous line width at low temperatures within this model was suggested. The temperature dependencies of the optical dephasing for two amorphous systems, polymethimetacrylate doped with tetra-tert-butylterrylene and zinc-tetraphenylporphine were calculated. Calculations were performed using the parameters known from the literature. The results were compared with the photon echo data for these systems, measured in the broad temperature range. It was found that the SPM describes the temperature behavior of the homogenous line width qualitatively correctly. At temperatures below 2 K, where the main contribution to optical dephasing is associated with tunneling two-level systems, the predicted line width values agree well with the experimental data. At higher temperatures, some difference between the prediction and experimental data was observed and attributed to the effect of impurity on the formation of quasilocal oscillations of the matrix.