Predicted electron transport coefficients and operating characteristics of CO2–N2–He laser mixtures

Abstract

Calculations have been made of transport coefficients of electrons in gas mixtures for ratios CO2:N2:He of 1:1:8, 1:2:3, 1:7:30, and 1:0.25:3. New cross sections for CO2 derived from swarm experiments are used together with previously published cross sections for N2 and He. Curves are presented of the predicted electron drift velocity, transverse and longitudinal diffusion coefficients, and ionization and attachment coefficients for E/N values ranging from 10−18 to 1 × 10−15 V cm2; E is the electric field strength and N the gas number density. Examples are given of derived distribution functions and comparisons are made with a Maxwellian distribution function. The percentage of the input electrical power which excites vibrational processes coupled to the 001 upper laser level of CO2 is given as a function of E/N. The maximum efficiency from these calculations increases for increasing ratios of N2:CO2, because the proportion of energy used to excite the bending and stretching modes of CO2 is then reduced. By assuming a recombination coefficient of 10−7 cm3 sec−1, the operating E/N for self-sustained glow discharges is predicted as a function of current density for various laser mixtures by equating the ionization rate to the attachment and recombination rate.

A TEA-CO2 laser oscillation by an inductive energy storage pulsed-power generator using a wire-fuse opening switch

“…Lowke and colleagues obtained electrical energy distribution functions for each E/N for a CO 2 /N 2 /He gas mixture [10]. Their method has been applied to a TE-CO 2 laser at greater than atmospheric pressures [11].…”

DC-excited cw CO₂ metal waveguide laser

“…But as shown in fig. 2-4, Lowke et al [38] found that the (001) cross section of Boness and Schulz [12] is about a factor of 3 too large to give consistent transport coefficients ( i.e. electron drift velocity, ionization and attachment coefficients).…”

“…and N 2 • Thus, electron energies sufficient to excite the upper laser level occurs at lower E/N [38].…”

“…7 e V. The beneficial role that He plays in a C0 2 laser discharge is to cool the gas by aiding in the depopulation of the lower laser level. He also plays a very important role in maintaining the energy distribution of electrons in the proper range [9,38]. …”

An analysis of transverse evolution of electron swarms in gases using moment equations and a propagator method

“…Values of D T in real gases were calculated using Boltzmann equation analyses, Monte Carlo simulations, and other numerical methods by Lowke et al (1973) for a CO 2 /N 2 /He mixture, Pitchford and Phelps (1982) and Phelps and Pitchford (1985) for N 2 , Makabe and Shimoyama (1986) and Koura (1987) for Ar or an Ar-like gas, Yachi et al (1991) and Date et al (1993) for CH 4 , etc. D T was also calculated for Ba + ions in Ar by Viehland (1994).…”