LASER COOLING BY SIGMA-SIGMA- CIRCULARLY-POLARIZED BEAMS OF UNEQUAL INTENSITIES()

The force on a multilevel atom in a ID Magneto-optical molasses with i mbalanced laser intensities is theoretically investigated. We employ a full quantum treatment to obtain the stationary momentum distribution of the atoms, for arbitrary parameters. The force exerted by the coun terpropagating laser beams balances for a non-zero locking velocity. T he dependence of this velocity on the intensity imbalance is found to be reduced by polarization gradient cooling. For certain values of the imbalance there are two stable velocites. and a splitting of the velo city distribution occurs. A small imbalance. or a magnetic field along the laser beams, can cause the sub-Doppler cooling to be lost. Howeve r, by the correct choice of parameters these effects can be made to ca ncel, and the sub-Doppler cooling is regained.