Population Densities of He Excited States in a Positive Column Discharge Used for the He-Cd+ Laser

The population densities of He excited states in a positive column discharge used for the He-Cd⁺ laser were measured as functions of Cd atom density, initial He pressure, and discharge current with the modified absorption method. They were also calculated with the aid of the electron energy distribution function obtained from the Boltzmann equation. It has been shown that the variations of the population densities of the He(I) 2³S and 2¹S states with the discharge current can be interpreted theoretically only when a new electronic collision process, He(2³S or 2¹S)+e→He(2³P or 2¹P)+e, is taken into account.