Relevance of beam statistical properties on light scattering

Abstract

This paper investigates the effects of the intensity and of statistical fluctuations in the mean energy and linewidth of the incident radiation upon the character of the light scattered by a many-level molecular system. This study involves the development of a completely quantum mechanical description of the time and frequency resolved light scattering with both excitation and detection treated in a symmetrical fashion. Incident radiation fluctuation and coherence properties are incorporated by the introduction of appropriate quantum mechanical states and statistical distributions. The theory is applied to the case of weak light sources and single photon absorption and emission processes. We consider two models of the exciting light, one with some coherence and the other totally incoherent, to elucidate the effects of photon quantum statistics and coherence. It is shown how the light scattering intensity for the partially coherent case is modified in an essential nonlinear fashion from what would be predicted by scaling a single photon incident light theory by the average number of photons incident on the molecule.