On the quantum theory of resonance scattering of atoms by light

B. A. Veklenko

The scattering of resonant radiation on an excited atom is considered. It is shown that the scattering cross section calculated with the help of quantum theory of radiation is five times larger than the one calculated using semi-classical theory. The quantum theory predicts, in general, the change in internal quantum statistical properties of light due to the scattering processes on excited atoms.

A. P. Kazantsev, Gregory I. Surdutovich, Valery P. Yakovlev +1 more

N. G. van Kampen

A. A. Villaeys, Karl F. Freed

The authors present a weak light field, scattering theoretical description of the intensity autocorrelation function for the scattered light from a many-atom (molecule) system. The theory considers both resonant and near-resonant scattering for atoms with many sublevels in both the ground and electronically excited states, and it incorporates the effects of the finite coherence time of the incident radiation. The theory is derived using incident two-photon wave packets with spatial dispersion among the target atoms. Purely anti-bunching contributions arise from single-atom-two-photon scattering and from successive two-atom-two-photon scattering events. However, there are interleaved two-atom-two-photon scattering processes which provide purely bunching contributions since both atoms may be scattering at the same time. Path length differences in the successive two-atom scatterings can also induce some bunching character to the correlation function. The dependence of the risetime and decay of the intensity correlation function upon the atomic excited state lifetimes and the coherence time of the incident light emphasises the correlation between photons which have been coherently and/or incoherently scattered.

C. Y. She, Jonathan S. Friedman

In Chapter 3, we move to a semiclassical treatment (quantum theory) of light absorption and scattering, specifically from atoms. We start with a description of how lidar measures Doppler shift, and the fundamental difference between the measurement when the laser is in resonance with an atomic transition (resonant) and when it is not (nonresonant). We follow with a treatment of quantum polarizability and the resulting absorption cross section, leading to the differential resonance scattering cross section and its contrast with the classical result. After quantum polarizability, we demonstrate the radiation pattern of coherently excited atoms. This takes us to an interpretation of the Hanle Effect. Following these descriptions of the phenomena that impact resonance lidar, we extend our understanding by closing the chapter with an overview of the rudimentary physics of sodium laser guide stars.