The process of energy transfer between excited sodium atoms

Two experiments were carried out to test a process proposed by Allegrini et al. as a viable explanation of the fluorescence from high lying levels which is observed when sodium vapor is illuminated by resonance radiation. In the first experiment a cell with sodium vapor was illuminated by a cw dye laser tuned to the 3S → 3P transition, and the linewidth and lineshape of the fluorescence from the 3D → 3P transition were measured. In the second experiment the cell was illuminated by two pulsed lasers, one tuned to the 3S → 3P resonance and the second well off resonance with this transition. The photoionization current was measured, as was the fluorescence intensity from the 6S → 3P and 5D → 3P transitions. We conclude that the Allegrini process does not significantly contribute to the populations in the 5D, 6S and 3D states.