Influence of the He-3 isotope on the output parameters of the He-Kr hollowcathode laser

The influence of the He-3 isotope as a buffer gas on the operating characte ristics of the He-Kr hollow cathode laser is studied. A comparison of the l aser output power and gain on the KrII 469.4 nm and KrII 431.8 nm lines in He-3-Kr and He-4-Kr gas mixtures is made and an increase of 33% is observed in the case of the He-3-Kr gas mixture. A simple qualitative analysis of t he plasma kinetics shows that the observed increase of the laser output par ameters is due to the increased rate constant for the excitation transfer r eaction and the increased density of the He(2 S-3(1)) metastable atoms and Kr ground state ions. The main reasons for this are the higher mean relativ e velocity of the colliding particles and the higher rate of electron cooli ng in He-3-Kr plasma. Peak output powers of 10 W and 1.5 W and small signal gains over the losses of 85% m(-1) and 64% m(-1) are measured for the blue and violet lines, res pectively, from a 21 cm active length at 17.5 kPa He-3 pressure, 17 Pa Kr p ressure and 96 A peak current. These values are significantly higher compar ed to earlier investigations. The operating discharge conditions are enlarg ed considerably; up to 21 kPa He pressure and 100 A peak current. The laser design chosen contributes to the achievement of this goal.