LASER OSCILLATION WITHOUT POPULATION-INVERSION IN A SODIUM ATOMIC-BEAM

Continuous wave (cw) amplification and laser oscillation without popul ation inversion have been observed for the first time in a Lambda sche me within the sodium D-1 line. This is also the first demonstration in which the lasing medium was an atomic beam; this is an approach which , in addition to elucidating the physics, lays a foundation for extens ions into the ultraviolet. Calculations using realistic atomic structu re were critical to the choice of experimental approach. Observations agree with full density-matrix calculations and clearly show there was no population inversion.