EXCITATION MECHANISMS AND GAIN MODELING OF THE HIGH-PRESSURE ATOMIC AR LASER IN HE/AR MIXTURES

The high-pressure (greater-than-or-equal-to 0.5 atm) atomic Ar laser (3d --> 4p) oscillates on four infrared transitions (1.27-2.4 mum). Quasicontinuous oscillation on the 1.79 mum transition has been obtained using electron beam and fission-fragment excitation over a wide range of power deposition and gas pressure. In this regard, a computer model has been developed to investigate excitation mechanisms of the Ar laser. Results from the model suggest that the upper laser level of the 1.79 mum transition [Ar(3d[1/2]1)] is dominantly populated by dissociative recombination of HeAr+. In contrast, the dissociative recombination of Ar2+ is believed to predominantly produce Ar(4s) states. Electroionization from Ar metastables at moderate to high pump rates is likely to be responsible for the high efficiency of the Ar laser. Gain and laser oscillation are discussed and compared to experiments for He/Ar ps mixtures using various Ar mole fractions and total pressures. These results show that the optimum Ar mole fractions in He/Ar mixtures are approximately 0.1%-5 % for quasicontinuous pumping.