Laser collimation of an atomic gallium beam

We have laser collimated a gallium atomic beam in one dimension using the linear-perpendicular-linear polarization gradient technique. Operating on the cycling 4p ²P_3∕2(F=3)→4d ²D_5∕2(F=4) transition at 294.45 nm, the full angular divergence of the atomic beam was reduced to 0.3 mrad, corresponding to a transverse velocity of ±11 cm∕s, about one-half the Doppler cooling limit. The dependence of the cooling efficiency on the laser detuning and power was investigated. Optical pumping of the atoms out of the 4p ²P_3∕2(F=3) state by the cooling laser was observed. Repumping schemes were investigated and found to successfully repopulate the cooled F=3 hyperfine state.