Excitation mechanisms of the N2+laser

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Abstract
A rate equation model capable of describing the reaction kinetics of the N2+ laser has been developed in order to investigate the possibility of long pulse or CW operation in this system. The difference in temporal behaviour of laser pulses on the 3914 AA transition compared to those of the 4278 and 4709 AA transitions (previously reported using short pulse excitation) can be interpreted as being due to the effects of a collisional process responsible for transferring population from the nu =1,2 into the nu =0 vibrational levels of the N2+ electronic ground state. It is suggested that this collisional process be identified with the symmetric charge transfer reaction of nitrogen on nitrogen. The model further suggests that even with longer excitation pulses the laser pulse duration will be limited by second-kind collisions of excited molecular nitrogen ions with plasma electrons. A discharge-excited nitrogen ion laser, in which the excitation pulse can be varied up to a maximum of 75 ns, has been constructed in order to test the predictions of the rate equation model. The experimental results support the conclusion that the laser pulse length at all wavelengths of the nitrogen ion system is limited by fundamental molecular kinetic processes.