Resonance Fluorescence under Finite Bandwidth Excitation

Abstract

With the development of increasingly precise experimental methods for studying the phenomenon of resonance fluorescence from atoms, as in atomic beam experiments, the need arises for a more realistic description of the excitation field in the theory. We have generalized our earlier quantum field treatment of the problem of resonance fluorescence from a two-level atom, [1, 2] to take account of the finite bandwidth of the exciting laser field. In the analysis we take the state of this field to be a statistical mixture of coherent states, in which the phase performs a random walk in time, and we ultimately average over the ensemble of phases. [3] We investigate the properties of the fluorescent light, and find some new features, that are absent under monochromatic excitation, and appear not to have been encountered in previous treatments of the problem. [4, 5] In particular, we show that the spectral density should become asymmetric under offresonance, non-monochromatic excitation.