Laser-induced flourescence studies of elementary processes in a helium plasma following He 3 ³P-2 ³S and 3 ¹P-2 ¹S excitation

We report experiments in which laser-induced fluorescence detection is incorporated into a flowing afterglow helium plasma to study the kinetics and dynamics of excited helium atoms. Following excitation of helium in the 3 ³P-2 ³S band at 388.9 nm, dispered fluorescence spectra show major features at 388.9, 706.5 and 587.6 nm corresponding to emission from the 3 ³P, 3 ³S and 3 ³D states as observed in previous studies. In addition to these major features, we also observe weaker, molecular emissions in the 430-500 and 7100-725 nm regions which we assign to fluorescence from He₂ states. Similar experiments in which the 3 ¹P-2 ¹S band at 501.6 nm is excited afford strong atomic fluorescence from the 3 ¹P and 3 ¹D states at 501.6 and 667.8 nm, respectively. A weak emission features can also be assigned to 3 ¹S-2 ¹P emission at 728.1 nm. Weak molecular emissions are again observed but in this case in the 440-470 and 535-600 nm regions.