Performance comparison of pulsed discharge and E-beam controlled CO2 lasers

Abstract

A pulsed CO2 laser model for axial pulse and TEA lasers is developed based on combining electric excitation with vibrational energy level kinetics and a laser cavity intensity model. The model is applied to electron-beam-controlled lasers by adding an electron-beam plasma generation component. Calculated results show the electron-beam laser has a maximum output energy efficiency approaching 20% if the input energy is sufficient to rapidly heat the gas to the self-terminating temperature, about 600 °K. Efficiencies higher than 20% have been achieved with pulsed discharge lasers but with a consequent penalty in output energy, because the state-of-the-art limits the amount of electrical energy input to less than that necessary to reach the self-terminating temperature in axial pulsed or TEA lasers. Results of kinetics studies suggested several approximations that permit analysis of laser performance for the self-terminating temperature condition. These approximations lead to a set of transcendental but closed form coupled expressions which yield solutions in good agreement with those obtained by exact kinetics treatment. Contour plots for a 1 mA/cm2 electron-beam laser, obtained from the closed form treatment, make it possible to determine the maximum laser energy output and efficiency for any given gas mixture. The upper bound on laser energy output was found to be 100 J/liter atmosphere.