Application of a diagram technique to the problem of resonance fluorescence from strongly driven two level atoms

Abstract

A Green's function formulation, valid for thermal as well as nonthermal equilibrium, is developed for the resonance fluorescence from strongly driven two level atoms. Translational motion and the Doppler broadening are also taken into account (collisions are considered in a second paper). The Feynman diagram technique is used to calculate the contribution of the physically important processes. The formulation is not based on the Markovian approximation or the quantum regression theorem. It takes full account of the dynamic Stark splitting and the saturation, and leads to a generalization of the "dressed atom" approach. Our "generalized dressed atom" (GDA) approach is valid for arbitrary values of the detuning and the pump field strength. The lowest order diagrams in the GDA picture give results equivalent to the existing theories. Some higher order diagrams are also considered. Although the resulting corrections are small, the physical processes involved are of some interest. These corrections include nonMarkovian effects.