EFFECT OF SCATTERED RADIATION ON SUB-DOPPLER COOLING

In this paper we discuss the effect of scattered radiation generated b y a gas of cold atoms on the temperature of the gas. We show that by t reating the reradiated held of the atoms as a fluctuating background h eld we can derive a master equation for a single atom where the effect of the surrounding medium is included in an effective relaxation oper ator. This relaxation operator is of second order in the interaction w ith the medium and in the binary-collision approximation can be writte n as the sum of two-body interactions with a correlation time equal to the natural lifetime of the atomic transition. The effect of the medi um on the two most important sub-Doppler cooling mechanisms, Sisyphus and motion-induced orientation cooling, is investigated analytically i n a one-dimensional model. In this we restrict ourselves to the limit of low saturation, weak background held and take the rate-equation lim it for the collision operator. We find that both mechanisms are very s ensitive to such a background field and that the temperature increases approximately as the number of atoms to the one-third power.