The formal structure of the time dependence of the state of an atom in a perturber bath in an intense classical monochromatic radiation field is studied. The authors allow the cross sections of binary collisions to be affected by the radiation field. The result is used to derive an expression for the collision-broadened saturated fluorescence excitation spectrum and absorption rate in terms of a collisional relaxation operator. This operator can be related to the rate of collisionally aided radiative excitation.
The authors derive an expression for the spectrum of fluorescence by a two-state atom in a perturber gas irradiated by nearly resonant monochromatic light of arbitrary intensity. The result is fully expressed in terms of the absorption profile that would be measured in a conventional low-intensity absorption experiment and of the rate of radiative and collisional transitions. The present result generalises previous work and the authors demonstrate that expressions obtained before in special cases are recovered by taking the appropriate limits.