Negative ion effects in TEA CO2 lasers

Abstract

Using sealed and flowing-gas TEA CO2 lasers the authors have determined that long-life arc-free operation can be obtained in sealed CO2-N2-He-O2-CO-H2-H2O mixtures provided the O2 concentration is less than 1/2-2%, depending on the particular laser, and the H2O concentration less than 1-3%. With a computer model of 63 neutral and negative ion processes the authors have calculated that the negative ion population is significantly increased with these amounts of added O2 and H2O and that CO4- and H- respectively become large compared with CO3- (the dominant ion in systems with little O2 or H2O). The beneficial effect of CO in suppressing negative ion formation is explained and the ratio of negative ions to electrons Nn/Ne is determined to be between 0.05 and 1.0 for a wide range of gas mixtures used in trigger-wire and UV pre-ionized TEA lasers.