Population inversion in hollow cathode, pulsed and positive column discharges

Firstly, a survey is given of excitation processes occurring in gas discharges, together with an analysis of selective excitation processes in gaseous optical masers. Hollow cathode discharges have been investigated as excitation media for gas lasers. Evidence is given for the establishment of a relationship between the 632.8nm helium-neon laser discharge and transition weak to strong discharges. An optimum electron temperature for oscillation on the 632.8nm line is indicated. In a pulsed helium-iodine discharge, oscillation is reported on four new laser transitions, one an intercombination transition. Simultaneous oscillation for the first time is reported on hyperfine components of the ionised iodine lines. Hyperfine intervals of the 6p and 6s levels have been established, giving agreement between calculated and observed hyperfine components of lines. These levels are shown to be strongly perturbed. An anomalous behaviour is reported on hyperfine oscillations on the658.5nm line, which can be attributed to non-equilibrium in the populationof hyperfine sublevels of the 6s level,due to pressure/current changes. Results support the proposal that charge transfer is the selective excitation mechanism in the helium-iodine laser.