2-DIMENSIONAL SUBRECOIL LASER COOLING

We report the first observation of subrecoil laser cooling in two dime nsions by velocity selective coherent population trapping. We have com pressed the momentum distribution of a cloud of trapped metastable hel ium atoms along two orthogonal axes to deltap = HBARk/4, where HBARk i s the photon momentum. The corresponding temperature, 16 times below t he single-photon recoil temperature, is 250 nK. Atoms are pumped into a nonabsorbing state exhibiting four well-resolved momentum peaks with subrecoil widths. The momentum space density in the peaks is signific antly greater than that in the uncooled distribution.