3 March 2014 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 alkali-exciplex (XPAL) laser systems. Scaling of these devices requires efficient generation of electronically excited metastable atoms in a continuous-wave electric discharge in flowing gas mixtures at atmospheric pressure. This paper describes initial investigations of the use of linear microwave micro-discharge arrays to generate metastable rare-gas atoms at atmospheric pressure in optical pump-and-probe experiments for laser development. Power requirements to ignite and sustain the plasma at 1 atm are low, <30 W. We report on the laser excitation dynamics of argon metastables, Ar (4s, 1s5) (Paschen notation), generated in flowing mixtures of Ar and He at 1 atm. Tunable diode laser absorption measurements indicate Ar(1s5) concentrations near 3 × 1012 cm-3 at 1 atm. The metastables are optically pumped by absorption of a focused beam from a continuous-wave Ti:S laser, and spectrally selected fluorescence is observed with an InGaAs camera and an InGaAs array spectrometer. We observe the optical excitation of the 1s5→2p9 transition at 811.5 nm and the corresponding laser-induced fluorescence on the 2p10→1s5 transition at 912.3 nm; the 2p10 state is efficiently populated by collisional energy transfer from 2p9. Using tunable diode laser absorption/gain spectroscopy, we observe small-signal gains of ~1 cm-1 over a 1.9 cm path. We also observe stable, continuous-wave laser oscillation at 912.3 nm, with preliminary optical efficiency ~55%. These results are consistent with efficient collisional coupling within the Ar(4s) manifold.
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W. T. Rawlins, W. T. Rawlins, K. L. Galbally-Kinney, K. L. Galbally-Kinney, S. J. Davis, S. J. Davis, A. R. Hoskinson, A. R. Hoskinson, J. A. Hopwood, J. A. Hopwood, "Laser excitation dynamics of argon metastables generated in atmospheric pressure flows by microwave frequency microplasma arrays", Proc. SPIE 8962, High Energy/Average Power Lasers and Intense Beam Applications VII, 896203 (3 March 2014); doi: 10.1117/12.2040083; https://doi.org/10.1117/12.2040083


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