Master equation theory applied to the redistribution of polarized radiation, in the weak radiation field limit. I. Zero magnetic field case

International audienceThis paper is devoted to describe the atom-radiation interaction in the formalism of non-relativistic quantum electrodynamics by means of a perturbative development extended to orders higher than 2. Atom and radiation are treated quantum mechanically, through the density matrix approach. Collision effects are also introduced, in the impact approximation. Polarization is taken into account. The following hypotheses are considered: (a) weak radiation field (stimulated emission is neglected with respect to spontaneous emission); (b) two-level atom; (c) unpolarized lower level; (d) atomic reference frame; (e) zero magnetic field. The perturbation series development has been summed. The result of the paper is twofold: (a) the profiles in the form of delta -functions obtained in ordinary theories extended up to order 2 in the series development are now replaced by realistic profiles: line-broadening is derived from the present formalism; (b) a new term (Rayleigh scattering term) appears at order 4 in the emissivity. This term is responsible for frequency coherence in scattering processes