Inverted population observation using pulsed optogalvanic effect

We report on the use of pulsed optogalvanic effect in the detection of inverted population. An early positive part of the optogalvanic signal is shown to be characteristic of a population inversion and is measured using a high temporal resolution from the start of the laser pulse. Such inversion is obtained on a few of the neon 3p → 3s transitions in a standard DC hollow-cathode discharge tube with neon buffer gas. We observed inverted optogalvanic signal with exciting laser wavelengths at 659.9 nm, 585.2 nm and others. In fact, transient laser transitions on some of these wavelengths, in fast neon discharges have been reported. The optogalvanic effects, corresponding to neon levels 1s₅ and 1s₂, and their dependent signals have opposite features and signs and are essentially mirror images of each other. The necessity of using pulsed optogalvanic mode and detection in the case of inverted population is discussed.