Pumping system with high specific energy characteristics, designed for an industrial CO₂laser

Abstract

A stationary cold recombining helium plasma is generated in an arc-heated magnetically trapped expanding plasma jet that was developed in the authors' laboratory. The plasma can be generated very stably and spectroscopic analysis is accomplished with sufficient accuracy. Population densities of the He I levels whose principal quantum numbers are 3-6 and 7 9.8 3D, 9 3D levels are observed spectroscopically. When the plasma comes downstream, the electron temperature and density become low and population inversion is obtained between some level pairs, such as 4'S-3'P and 43P-33D. The degree of inversion is insufficient to be used for lasing. The electron temperature as found by Eoltzmann plots of the higher states drops to about 0.2 eV in the downstream expansion. The electmns are cooled by contact with cold residual gas. The magneticconfinement of the plasma jet is adequate to cause large population inversions without decreasing the electron density. The experimental results are explained in terms of a calculation based on a collisional radiative model including an optical thickness. The mechanisms of formation of DoDulation inversions are discussed in terms of atomic processes.