Velocity-specific atomic-state selection in an atomic beam by continuous-wave optical pumping

We present experimental results demonstrating strong velocity-distribution modification in a specific atomic state using optical pumping between hyperfine split levels. These results show that the velocity of a specific state can be defined within 6%, corresponding to a local temperature of 1 K. The velocity-specific-state selection is accomplished by using a nearly effusive atomic beam of sodium and a single frequency-stabilized dye laser.