DIPOLE FORCE LASER COOLING IN MULTILEVEL ATOMS

We have observed sub-Doppler cooling using an intense, blue-detuned st anding wave and a traveling wave in a multilevel atomic system. We mod el the system as a three-level atom and calculate the exact velocity-d ependent force using a matrix continued fraction method. Like the dipo le force in a two-level atom, the three-level force does not saturate with the intensity of the driving fields, but for a given intensity, t he force in the three-level system can be considerably larger. The mec hanism providing the force in the three-level system can be understood using a dressed-state model. We demonstrate the effect by cooling Li- 7 atoms in one dimension.