A TIME-DEPENDENT 2 ELECTRON GROUP MODEL FOR A DISCHARGE EXCITED HE-SR RECOMBINATION LASER

A time-dependent two electron group model 2EGM, based on a bi-Maxwellian electron energy distribution function (EEDF), has been developed to simulate the discharge kinetics in a high-current, high-repetition frequency, pulsed He-Sr recombination laser. A comparison is made between the results predicted by 2EGM and 1EGM (Maxwellian) simulations and experimental data corresponding to typical operating conditions of the laser. Results from the 2EGM indicate that during the current pulse, the high-energy tail region of the EEDF is severely depleted due to both inelastic collisions between electrons and ground state helium atoms and incomplete thermalization via Coulomb collisions. This leads to a highly non-Maxwellian EEDF, a feature which cannot be accommodated in the 1EGM simulation. In addition, the He*(2(3)S), Sr, and Sr+ population densities predicted by the 2EGM are shown to be in close agreement with the experimental data, whereas the 1EGM predicts a partitioning of energy between helium and strontium states which is inconsistent with the observed population densities.