Radiation-induced modification of the atomic momentum distribution in a traveling-wave resonant light field

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Abstract
A quantum-mechanical transport equation of the Boltzmann type is proposed for the momentum-distribution function of atoms in the field of a quasiresonant traveling light wave. The physical meaning of the solution is discussed in terms of the linear momentum transferred from the photons to the atoms through a succesion of photon-scattering processes, the number of which follows a Poisson law. A connection is established with the random-flight problem. The analytical expression of the radiation-modified atomic-momentum-distribution function is derived explicitly. The first and second moments of the distribution correspond to a drift (associated with an average force) and a smearing out (associated with an anisotropic diffusion tensor), respectively. The latter effect is shown to arise from the dispersion in both the number and the direction of the scattered photons.