Anomalous behaviour in the saturation of the sodium D lines under high power laser illumination

Abstract

The authors have confirmed earlier observations that fluorescence from dense sodium vapour under high power illumination does not saturate with increasing laser intensity. Direct observations of level population using a variant of the interferometric hook technique with a time resolution of ten nanoseconds have been performed, showing that the level populations of the pumped transition were in the ratio of their statistical weights. The apparent contradiction between this result and that of the laser-induced fluorescence observations is considered.