Time-resolved analysis of a transversely excited nitrogen laser

Abstract

Time-resolved measurements have been made of stimulated and spontaneous emission, voltage and current in a transversely excited nitrogen laser giving 50 kW peak power at 337 nm. The excitation rates to the laser levels were calculated from literature data using the results of electrical measurements, a check being obtained from measurements of spontaneous emission. The Druyvesteyn electron energy distribution gives better agreement with measurements than the Maxwellian. Laser pulses were calculated by solving numerically the space-dependent rate equations for population and photon number densities. Recent literature data on the transition probabilities and the pressure-dependence of the lifetime of the upper laser level were introduced into the calculations. The formation of a thin discharge channel was found to be essential for the high gain achieved. The onset of stimulated emission as observed on oscilloscope pictures was found to have a delay of the order of 1 ns in relation to the onset of current and spontaneous emission. This delay was confirmed by the calculations and explained as the time required to build up the population inversion and radiation density.