Xenon excited-state densities in electron-beam pumped XeCl and XeF

Understanding of the neutral channel formation kinetics in excimer laser gas mixtures has been limited by the lack of data on the pertinent excited-state populations in these mixtures. Presented are time-dependent measurements of the lower level xenon excited-state densities in electron-beam (e-beam) pumped XeCl and XeF laser mixtures (neon diluent). Measurements are obtained using hook interferometry under nonlasing conditions at an average excitation rate of ≊250 kW/cm³ and e-beam pulse lengths of 0.4 and 1 μs. The population differences, ΔN*, between four different electronic transitions [three in the Xe*(6s)-Xe**(6p) manifold, and one in the Xe**(6s')-Xe***(6p') manifold] are examined as a function of halogen concentration. For both XeCl and XeF at high initial halogen concentrations (>4 Torr), the ΔN* densities of the Xe*(6s) and Xe**(6s') transitions are relatively constant during the 0.4-μs e-beam pulse [for ΔN*(6s-6p): ≊4×10¹⁴ cm^-3 for XeCl, and ≊1.5×10¹⁴ cm^-3 for XeF]. At lower initial halogen concentrations, the ΔN* densities of 6s-6p and 6s'-6p' start at the beginning of the pulse at approximately the same densities as the richer halogen mixtures, but at a certain point during the pulse, the ΔN* densities abruptly increase. This increase can be >10 times for very lean halogen mixtures (1-2 Torr), and occurs at earlier times as the initial halogen concentration is reduced. From other measurements, this increase appears related to the depletion of the halogen. The observed lifetime of the Xe*(6s) densities is ≊2 μs for the low initital halogen concentration mixtures. Additional density data for halogen-free Ne/Xe and Ar/Xe mixtures are also presented.