Effect of Helium on Population Inversion in the Helium-Neon Laser

Measurements are given of the ratio of the excitation due to helium to the excitation due to electrons for the 3s and the 2s levels (Paschen notation) of neon. The ratio was obtained from spectral intensity measurements on dc discharges in pure neon and in helium-neon mixtures with the electron temperature the same in the two cases. The excitation ratios for the Ne 3s levels at a discharge current density of 130 mA cm−2 in a 5:1 He–Ne mixture are 3s2−72, 3s3−4, 3s4−7, and 3s5−7; and for the Ne 2s levels in a 10:1 He–Ne mixture, 2s2−11, 2s3−20, 2s4−5, and 2s5−10.