Heavy-ion versus electron-beam excitation of an excimer laser

A model is described for the heavy-ion pumping of an XeF(B) laser by uranium fission fragments (FF).The model is a self-consistent accounting of the generation and transport of the FF’s through the fission foils, slowing of the fragments in the gas, evolution of the secondary-electron-source function and distribution, and the XeF laser plasma kinetics. By simulating the same quantities for an e-beam-pumped plasma, direct comparisons can be made for laser performance. We found that the secondary-electron source generated by the e-beam is more energetic than that for direct ionization by FF’s due to a more favorable mass ratio for momentum transfer collisions with orbital electrons. This difference in the electron-source functions significantly affects W values and excitation fractions. The impact on laser performance, though, is not large due to the high efficiency of channeling deposited energy to the upper laser level in XeF lasers. For conditions typical of FF excitation (power deposition 1–3 kW cm−3, pulse length ≊200 μs), e-beam excitation results in 10%–15% higher gain than heavy-ion excitation.