Self-cooling in a system of driven two-level atoms

We investigate the evolution of a system of two-level atoms interacting with two counterpropagating radiation fields including the effects of atomic centre-of-mass motion. The analysis involves the numerical solution of a set of generalised Maxwell-Bloch equations. It is shown that, under different conditions, lasing in a system of non-inverted two-level atoms may be obtained due to the formation of either a population difference grating or a density grating. Furthermore a novel self-cooling effect within the driven atomic system is demonstrated and a possible experiment for the observation of this effect is described. This self-cooling is an example of phenomena in which both population difference grating effects and atomic centre-of-mass motion play a role