Non-Lorentzian spectral diffusion line shapes in glasses: Analysis based on the two-level-system model

摘要

The dynamics of tunneling two-level systems (TLSs) or other slowly relaxing objects in glasses cause a diffusional boradening of the line shapes of chromophore impurity molecuels. The standard tunneling TLS model for glasses predits that the diffusional broadening is Lorentzian. Recently non-Lorentzian absorption line profiles of chromophores were discovered in a series of glasses by means of optical hole burning spectroscoy. This paper attempts to analze possible reasons for the mon-Lorentzian line shapes. The standard model is modified to account for the dispersion of the chromophore-TLS coupling strengths, for TLS concentration inhomogeneities, and for chromophore-TLS interactions other than dipolar. It is foudn that in general the above modifications lead to line shapes, which are more peaked at the center and show more pronounced wings than a Lorentzian of the same width, in agreement with the experimental observations.