Fluorescence of sodium vapour excited by 330 nm laser pulses

We report results of investigation on the fluorescence induced in sodium va pour by pulses of laser light tuned near the 3S --> 4P transition (330 nm). The fluorescence was observed in perpendicular and parallel directions in respect to the laser beam. A depletion of fluorescence intensity correspond ing to the 5D --> 3P transition (498 nm) was observed along the laser beam. We explain this effect as a result of reabsorption that is caused by inten se population of the 3P level due to cascade stimulated processes. The most intense depletion occurs about 20 ns after the laser pulse and it correspo nds to the moment of maximal population of the 3P level.