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Enhanced IR hollow cathode laser in a 3He–Ne gas mixture

An experimental and theoretical study on 3He–Ne and 4He–Ne helical hollow cathode lasers is presented. Enhanced laser operation on the near IR NeI lines is observed when the natural isotope 4He is substituted by the lighter isotope 3He. A four-fold increase in the laser output power and a three-fold increase in the laser gain for the strongest NeI 1.1523 µm line is measured in the 3He–Ne gas mixture compared to the 4He–Ne gas mixture. On the basis of the theoretical analysis done by means of a non-stationary kinetic model for the negative glow plasma of 3He–Ne and 4He–Ne hollow cathode lasers, a study on the changes in the particle kinetics is carried out and an explanation of the experimental results is proposed. In the 3He–Ne mixture the electron temperature is lower than in the 4He–Ne mixture, while the gas temperature is higher. As a result the helium triplet metastable density and the rate constant for excitation transfer to neon atoms are higher in the 3He–Ne mixture. The lower laser level de-excitation due to intra-multiplet mixing of 2p1–10levels by 3He atoms is more efficient.