Investigations of a discharge-excited short-pulse xenon monochloride laser

Abstract

<p>Experimental and theoretical investigations have been carried out for a compact, UV-preionized, discharge-excited, short-pulse XeCl laser. A comprehensive description of the molecular states and the potential-energy curves for XeCl is provided. The possible radiative transitions are determined according to the selection rules for electric-dipole transitions. An electron-jump model, based on the pseudo-crossings of the potential-energy curves of the ionic states and Rydberg states, is developed to calculate the formation rate-coefficient of the exciplex XeCl*. The results from this model are in good agreement with the results of earlier models discussed in the literature. Furthermore, this model suggests two additional important channels for the formation of XeCl*. As well, the model can be used to evaluate the rate-coefficients for each individual dissociative channel for XeCl*. The compact laser system has an active discharge volume of ≈1 cm³, providing ≈1 mJ output energy in a pulse duration of ≈1 ns. This corresponds to a peak output power of ≈1 MW. Until very recently, this was the shortest duration pulse produced directly in a discharge-excited excimer laser. The typical operation of the laser employed a 0.8%Xe/0.3%HCl/He gas mixture at a total gas pressure in the range from 350 kPa to 450 kPa, and a capacitor charging voltage of 15 kV. Discharge voltage waveforms were measured by using a fast-response Pockels cell. The time resolution for these measurements was better than 1 ns. Discharge current waveforms were measured using a fast-response Rogowski coil. These waveform data were used to evaluate parameters such as inductance and resistance in the excitation circuit, and for comparison with the results from the model. The model, which is self-consistent and concise, combines the models for both the kinetic processes and for the excitation circuit. In the kinetic model for the discharge, only 40 kinetic processes involving 13 chemical species, plus photons and electrons, are required. These 40 processes, chosen from a much larger number of possible processes, are the only ones with sufficiently large rate-coefficients to influence a short-duration discharge. For the model, use is made of the Boltzmann equation for a spatially-homogeneous medium to solve the electron energy distribution. The validity of the model is demonstrated by the good agreement between the calculated and measured waveform data for discharge voltage, current and resistance, and for laser output in terms of waveform, peak power, total energy, and delay time to the onset of laser emission. This model is very useful for the analysis of the kinetics for short-pulse XeCl lasers, and for optimizing the performance of these lasers.</p>