Kinetic model of the active medium of a He — Ar laser pumped by a hard ioniser

Plasma jet devices that use a helium gas flow mixed with a small percentage of argon have been shown to operate with a larger discharge current and enhanced production of the Ar(1s5) metastable state, particularly in the discharge afterglow. In this experiment, time-resolved quantitative measurements of He(23S1) and Ar(1s5) metastable species were combined with current and spectrally resolved emission measurements to elucidate the role of Penning ionization in a helium plasma jet with a variable argon admixture. The plasma jet was enclosed in a glass chamber through which a flowing nitrogen background was maintained at 600 Torr. At 3%–5% Ar admixture, we observed a ∼50% increase in the peak circuit current and streamer velocity relative to a pure helium plasma jet for the same applied voltage. The streamer initiation delay also decreased by ∼20%. Penning ionization of ground-state argon was found to be the dominant quenching pathway for He(23S1) up to 2% Ar and was directly correlated with a sharp increase in both the circuit current and afterglow production of Ar(1s5) for Ar admixtures up to 1%, but not necessarily with the streamer velocity, which increased more gradually with Ar concentration. Ar(1s5) was produced in the afterglow through recombination of Ar+ and dissociative recombination of Ar2+ as the local mean electron energy decreased in the plasma channel behind the streamer head. The discharge current and argon metastable enhancement are contingent on the rapid production of He(23S1) near the streamer head, >5×1012 cm−3 in 30 ns under the conditions of this experiment.

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Argon metastable production in argon-helium microplasmas

Hoskinson

Gregório

Hopwood

et al. 2016

Journal of Applied Physics

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Microwave resonator-driven microplasmas are a promising technology for generating the high density of rare-gas metastable states required for optically pumped rare gas laser systems. We measure the density of argon 1s5 states (Paschen notation) in argon-helium plasmas between 100 Torr and atmospheric pressure using diode laser absorption. The metastable state density is observed to rise with helium mole fraction at lower pressures but to instead fall slightly when tested near atmospheric pressure. A 0-D model of the discharge suggests that these distinct behaviors result from the discharge being diffusion-controlled at lower pressures, but with losses occurring primarily through dissociative recombination at high pressures. In all cases, the argon metastable density falls sharply when the neutral argon gas fraction is reduced below approximately 2%.

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Kinetic model of the active medium of a He — Ar laser pumped by a hard ioniser

Cited by 5 publications

References 37 publications

Lasing Mechanisms and Kinetic Models of NPLs

Lasing Mechanisms and Kinetic Models of NPLs

Role of Penning ionization in the enhancement of streamer channel conductivity and Ar(1s5) production in a He-Ar plasma jet

Argon metastable production in argon-helium microplasmas

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