Atom Cooling By Partially Spatially Coherent Lasers

Atom cooling and trapping by partially spatially coherent lasers is investigated both experimentally and theoretically. The degree of spatial coherence of the laser beams is controlled by the electro-optic crystal. The characteristics of the trapped atomic cloud are studied. The experimental results indicate that the atom number and atomic Gaussian density distribution stay unchanged due to the fact that the average photon scattering rate is independent of the spatial coherence of the laser beams. However, the measured temperature of the atomic cloud increases as the degree of spatial coherence of the laser beams decreases. The reason is that the scattering force of the partially spatially coherent lasers acting on the atoms fluctuates temporally and spatially, which broadens the velocity distribution of the atoms.