Electron energy deposition in an electron-beam pumped KrF amplifier: Impact of beam power and energy

The electron deposition in an Ar-Kr-F-2 mixture, based on a solution of the electron Boltzmann equation, is presented. The model is relevant to an electron-beam generated KrF* laser amplifier at atmospheric pressure. Sets of cross sections for Ar, Kr, and F-2 have been compiled. Calculations have been performed to determine the electron energy distribution function, energy per electron-ion pair and the ionization and excitation rates. It is found that the inclusion of inner shell ionization and the subsequent Auger emission are essential for matching known results on both the energy per electron-ion pair W-ei and the stopping power in pure Ar or Kr target gases. For the chosen Ar-Kr-F-2 mixture, W-ei is calculated to be 24.6 eV. The excitation-to-ionization ratio is calculated to be 0.38 for Ar and 0.54 for Kr at low input power density P-beam (1 kW/cm(3)). Both ratios increase with P-beam, particularly for Kr which attains 0.8 at 1 MW/cm(3). The dependency on P-beam and the excitation efficiency for Kr is significantly higher than previously assumed in KrF* kinetic models. Results are also compared with the continuous slowing down approximation to demonstrate that this approach is limited to the regime of low power deposition. (C) 2002 American Institute of Physics.