Nonimpact theory of resonance Raman line shapes in strong radiation fields

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,). To lowest order (n=2) the spectrum is expressed in terms of the three ordinary line-shape functions corresponding to the ab, bc, and 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.