Influence of the³He isotope on the output parameters of the He-Kr hollow cathode laser

Abstract

The influence of the 3He isotope as a buffer gas on the operating characteristics of the He-Kr hollow cathode laser is studied. A comparison of the laser output power and gain on the KrII 469.4 nm and KrII 431.8 nm lines in 3He-Kr and 4He-Kr gas mixtures is made and an increase of 33% is observed in the case of the 3He-Kr gas mixture. A simple qualitative analysis of the plasma kinetics shows that the observed increase of the laser output parameters is due to the increased rate constant for the excitation transfer reaction and the increased density of the He(2 3S1) metastable atoms and Kr ground state ions. The main reasons for this are the higher mean relative velocity of the colliding particles and the higher rate of electron cooling in 3He-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, respectively, from a 21 cm active length at 17.5 kPa 3He pressure, 17 Pa Kr pressure and 96 A peak current. These values are significantly higher compared to earlier investigations. The operating discharge conditions are enlarged considerably; up to 21 kPa He pressure and 100 A peak current. The laser design chosen contributes to the achievement of this goal.

Enhanced IR hollow cathode laser in a3He–Ne gas mixture

“…The observed results for the behaviour of the peak output power and the peak small signal gain on the NeI 1.1523 µm line by increasing the discharge current in 3 He-Ne and 4 He-Ne gas mixtures, at optimal helium and neon pressures, are shown in figures 2 and 3, respectively. It can be seen that the output power is about four times higher and the gain is about three times higher in the 3 He-Ne gas mixture.…”

“…A comparison of the laser output power and small signal gain for the three IR lines when 4 He and 3 He are used as buffer gases is carried out. The dependence of the output power on the discharge current in the 3 He-Ne gas mixture has similar behaviour to the 4 He-Ne gas mixture, but the values measured for the output power and the small signal gain are considerably higher, by several times. The threshold currents for lasing are almost the same in both gas mixtures.…”

“…On the basis of the non-stationary kinetic model of the He-Ne-Ar-H 2 laser published in [10], a kinetic model for plasma-chemical and radiative processes in the negative glow of 3 He-Ne and 4 He-Ne hollow cathode lasers is developed. The NeI 1.1523 µm line (2s 2 -2p 4 transition) is considered.…”

“…If the natural isotope 4 He is substituted by the lighter isotope 3 He, the following changes in the particle kinetics will take place:…”

“…In the 3 He-Cu hollow cathode laser the output power on the CuII 780.8 nm line is increased by about 30% [3]. In our previous investigation on He-Kr hollow cathode lasers [4] it was demonstrated that the output power and the gain on the KrII 469.4 nm and KrII 431.8 nm lines increases by about 33% when the natural isotope 4 He is replaced by the lighter isotope 3 He.…”