Spectral line shapes of impurity centers in solids at low temperatures

The paper briefly overviews a master equation theory for the case of a single pseudolocal vibration interacting with an electronic molecular transition, a phonon bath, and laser irradiation. The theory is valid for a broad range of laser powers. At low laser powers it was compared to sudden-jump model. Qualitatively, both theories predict that in addition to the conventional Lorentzian, the line consists of a dispersive component in the core region and a side band. Quantitatively, the sudden jump model is applicable only if the vibration–phonon coupling is independent of the electronic wave functions. An interesting property of the complex line was found at strong excitation. In this case the line first behaves in a fashion intermediate to the saturation behavior of homogeneously and inhomogeneously broadened spectra. But as the laser intensity is growing, the interaction with optical field “suppress” the dephasing caused by the interaction with the matrix and the line becomes a Lorentzian.