Redistribution of the atom velocities induced by light

The redistribution of the velocities of atoms in a low pressure gas induced by light is considered within the framework of the weak collision model. A consistent deduction of an equation of the Fokker-Planck type for atoms in a resonant light field is presented. It is shown that the diffusion coefficients for atoms in momentum space are, in the case of a travelling wave, restricted by the rate of spontaneous decay, whereas for a standing wave they increase proportionally to the light intensity. The minimum cooling temperature of the atoms achievable by the light action is found. It is demonstrated that in principle the formation of narrow dips in the momentum distribution should be possible, their width, as measured in frequency units, being of the order of the homogeneous width