Laser fluorescence experiments with a pulsed dye laser in an argon plasma

We have carried out laser-induced fluorescence experiments in the argon plasma of a hollow cathode arc (HCA) using a pulsed-dye laser. The pumping line was the 611.5 nm transition between the metastable 3d'2G and the 4p'2F level in the argon-ion system (' refers to the 1D core of the two times ionized argon atom). From the measured fluorescence signal of the 4p'2F upper level, we are able to determine the deexcitation coefficient [(2.5±1.0) 10-14 m3 sec-1] and the density of the 3d'2G metastable level (1.5×1015-1.25×1016 m-3). The 3d'2G metastable doublet is a serious candidate for excitation of the 4p upper laser levels and may partly be responsible for the 4s-4p inversion which causes the argon-ion laser oscillation.