Model description of the dephasing of optical impurities in glasses

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Abstract
A microscopic model is used to calculate the optical line shape of impurities in amorphous hosts. The dynamics of the glass are described by an ensemble of two-level systems which interact with the phonons of the matrix and which are coupled to the impurity. Within linear-response theory, a line-shape expression is derived. Equations of motion for the pertinent correlation functions are obtained through Mori’s formalism and solved approximately for the full many-body problem. Discussing the line-shape expression, we justify an averaging procedure for the description of the linewidth. Numerical linewidth calculations are presented, and several ways to explain the temperature dependence of experimentally observed linewidths within the model are discussed.