Model of optogalvanic effects in the neon positive column

An experimental and theoretical investigation of the 594.5-nm optogalvanic effect in the Ne positive column is described. The effect is a decrease in discharge conductance due to laser-induced depletion of metastable atoms. Absolute measurements of the effect per unit of absorbed laser power are reported for a wide range of discharge conditions. Postive-column discharges with radius-pressure products of 0.1-1.0 cm Torr and with sustaining direct currents of 1-16 mA are studied. The effect is modeled in this regime by applying perturbation theory to key rate equations that describe the discharge. The model predictions are in agreement with the experimental measurements. Absolute densities of atoms excited to the $2p^{5}3s$ levels are also reported. The regime studied covers the transition from a discharge sustained primarily by single-step electron-impact ionization to a discharge sustained primarily by two-step ionization via the $2p^{5}3s$ metastable levels. The global power balance of the discharge is dominated by wall losses of atoms excited to the $2p^{5}3s$ levels at all pressures and currents studied.