Nonimpact theory of resonance Raman line shapes in strong radiation fields

Abstract

We develop an expansion for the resonance Raman line shape of a three-level system $|a〉$, $|b〉$, and $|c〉$ in an arbitrary strong radiation field, being perturbed by dephasing collisions with foreign gas particles. The microscopic information relevant to the line broadening is expresssed in terms of a hierarchy of $n$-time correlation functions of the transition dipole operator ($n=2,4,6,\dots$). To lowest order ($n=2\mathrm{}$) the spectrum is expressed in terms of the three ordinary line-shape functions corresponding to the $\mathrm{ab}$, $\mathrm{bc}$, and $\mathrm{ac}$ transitions. The present theory is not restricted to the impact limit and, depending on the collision time scale, may yield very different results from the well-known impact spectra. Explicit calculations of the predicted spectra are presented for a model system.