Measurement and calculation of the gain and of the vibrational temperatures in a CO2 gasdynamic laser

Measurements of the intensity of spontaneous infrared radiation emitted by the active medium of a CO₂ gasdynamic laser in the form of bands at 4.3 and 2.7 μ were used to determine the vibrational temperatures of the asymmetric and combination modes of CO₂, and to calculate the gain for the 00⁰1 → 10⁰0 laser transition. Measurements were also made of the gain using a probe laser beam. Mixtures of the compositions CO₂:N₂:He = 1:4:5 and CO₂:N₂ = 1.9 were investigated for various parameters of the gas in front of the nozzle. A good agreement was obtained between the results of measurements of the gain by two independent methods, which demonstrated that the "spontaneous" method for the diagnostics of CO₂ gasdynamic lasers was reliable. Measurements of the vibrational temperatures of gaseous carbon dioxide revealed a more rapid relaxation of the asymmetric CO₂ mode than the relaxation predicted theoretically.