Time evolution of the population inversion between (A ³ Sigma _u⁺, v") and (B ³ Pi _g, v') states in the positive column of a nitrogen pulsed discharge

Time transients of population difference between A ³ Sigma _u⁺ (v"=0) and B ³ Pi _g (v'=2) states were measured in a positive column of moderate-current nitrogen pulsed discharge. The population difference was evaluated from integrated high-resolution laser absorption/gain profiles. Optical gain, due to the population inversion, was present during the first 3-6 mu s of the discharge pulse. The population difference was 0.3*10¹² at the peak current of 1 A. Experiments were done at 0.5 Torr pressure and current densities in the range from 0.6-16 A cm^-2. The simple kinetic model, which includes collisions with electrons and molecular nitrogen, and takes into account vibrational excitation of N₂(X), reproduces surprisingly accurately the measured time transients of population difference.