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6 July 2016 Laser excitation dynamics of argon metastables generated in atmospheric pressure flows by microwave frequency microplasma arrays
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The optically pumped rare-gas metastable laser is a chemically inert analogue to diode-pumped alkali (DPAL) and alkaliexciplex (XPAL) laser systems. Scaling of these devices requires efficient generation of electronically excited metastable atoms at number densities in excess of 1012 cm-3 in a continuous-wave electric discharge in flowing gas mixtures with helium diluent. This paper describes continuing investigations of the use of linear microwave micro-discharge arrays to generate metastable argon atoms, Ar (4s, 1s5) (Paschen notation), in flowing mixtures of Ar and He at atmospheric and reduced pressures, in optical pump-and-probe experiments for laser development. We describe initial experimental investigations of several key aspects of concepts for scaling to higher output powers. This includes initial data on the dependence of argon metastable production and optically pumped gain on micro-discharge gap size, pressure, and discharge power. We have observed clearly measureable gain at pressures down to 85 Torr. We have also developed an overlapping dual-array micro-discharge-flow configuration, to conduct detailed measurements of Ar(1s5) production and loss. Spatially resolved measurements of Ar(1s5) distributions in discharge-flow provide preliminary indications of 20-50 μs collisional lifetimes of argon metastable atoms after they exit the active microplasma. This information is relevant to modeling the recycling of Ar(1s5) in the optically pumped laser, and to the scaling architecture of the optically pumped system. The dual-discharge investigations demonstrate the potential for volume scaling of the active gain medium in a simple multi-discharge, flow-through configuration.
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W. T. Rawlins, K. L. Galbally-Kinney, S. J. Davis, A. R. Hoskinson, and J. A. Hopwood "Laser excitation dynamics of argon metastables generated in atmospheric pressure flows by microwave frequency microplasma arrays", Proc. SPIE 9729, High Energy/Average Power Lasers and Intense Beam Applications IX, 97290B (6 July 2016);

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