Five-level argon–helium discharge model for characterization of a diode-pumped rare-gas laser

A five-level discharge kinetics model is developed to characterize the scaling potential of the diode-pumped rare-gas laser. The predicted excited state populations are examined as functions of the gas pressure, gas temperature, electron density, and electron temperature. The density of the metastable Ar(1s5) level is a sensitive function of electron temperature, increasing from 1012 cm−3 at 1 eV to 5×1013 cm−3 at 1.2 eV, for a total pressure of 400 Torr and a gas temperature of 440 K. This is in contrast to the distribution among excited states, which are most sensitive to the electron density and result from the interplay of the electron-impact and neutral-impact spin-orbit mixing rates. The model is benchmarked using absorption, emission, and gain data from recent laser demonstrations. A metastable number-density/path-length product of 1×1014 cm−2 is required for optimal lasing performance at a strong pump intensity of 20 kW/cm2. This system requires an aperture of 6.9 cm2 in order to sustain 100 kW performance in the total volume of 69 cm3. The primary difficulty in the development of such a discharge system is due to the combined requirements of a large-volume, homogeneous, atmospheric pressure discharge with sufficient electron temperature to sustain significant production of the metastable 1s5 state.