Production of radical species by electron beam deposition in an ArF* lasing medium

Abstract

The electron-beam-pumped ArF laser is a laser technology capable of providing very high lasing energies at the shortest wavelength (λ = 193 nm) among the rare gas halide lasers and therefore has the potential to be a superior driver for inertial fusion. The electron kinetics are rigorously treated by numerically solving the steady-state, spatially averaged electron Boltzmann equation in Ar-F2 gas. The e-beam energy deposition and collisional reaction rates with electrons are calculated from the electron energy distribution function for a wide range of e-beam deposition powers (Pbeam = 10 kW/cm3–3 MW/cm3) and fluorine concentrations (xF2 = 0.01 – 10%). The rates are reduced to a set of coefficients that are fitted with analytical formulas as a function of two universal parameters: Pbeam/p and xF2, where p is the gas pressure. It is found that in the regime of high e-beam power deposition, the fluorine molecules are rapidly destroyed through dissociative attachment and neutral dissociation. The loss of F2 over the duration of the beam is proportional to the e-beam energy deposition per unit volume, εbeam, and follows ΔnF2(cm−3)≅4×1017εbeam(J/cm3), in agreement with experimental data. The fluorine molecule conversion to other fluorine species, including atomic fluorine, is shown to have a very small effect on the index of refraction even at percent level concentrations.