Kinetics of Metastable Argon Optical Excitation and Gain in Ar/He Microplasmas

Abstract

The optically pumped rare-gas metastable laser is capable of high-intensity lasing on a broad range of near-infrared transitions for excited-state rare gas atoms (Ar*, Kr*, Ne*, Xe*) diluted in flowing He. The lasing action is generated by photoexcitation of the metastable atom to an upper state, followed by collisional energy transfer with He to a neighboring state and lasing back to the metastable state. The metastables are generated in a high-efficiency electric discharge at pressures of ∼0.4 to 1 atm. The diode-pumped rare-gas laser (DPRGL) is a chemically inert analogue to diode-pumped alkali laser (DPAL) systems, with similar optical and power scaling characteristics for high-energy laser applications. We used a continuous-wave linear microplasma array in Ar/He mixtures to produce Ar(1s5) (Paschen notation) metastables at number densities exceeding 1013 cm–3. The gain medium was optically pumped by both a narrow-line 1 W titanium-sapphire laser and a 30 W diode laser. Tunable diode laser absorption and gain spectroscopy determined Ar(1s5) number densities and small-signal gains up to ∼2.5 cm–1. Continuous-wave lasing was observed using the diode pump laser. The results were analyzed with a steady-state kinetics model relating the gain and the Ar(1s5) number density.

Demonstration of a diode-pumped dual-wavelength metastable krypton laser

“…Wang et al [8,9] recently proposed a new scheme for extracting lasing in a plasma jet, potentially overcoming the power-scaling obstacles in previously used confined discharges. Until now, most research on DPRGLs has been carried out using Ar* as the gain medium [15][16][17][18] and a little on the Xe* laser [5,19,20] . The only research for the Kr* laser is on concept verification and kinetics investigation [1,21] , and no study using high-power diode pumping has been reported.…”