Vibrational-Rotational Laser Action in Carbon Monoxide

In this paper we give details of the laser action on rotational transitions of 10-9, 9-8, 8-7, 7-6, and 6-5 vibrational bands belonging to the ground electronic state ($X{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}$) of CO. Laser action is produced in a low-pressure CO pulsed discharge. A comparison between the measured laser wavelengths (accuracy of ±0.5 Å at 5.0-5.4 μ) and wavelengths calculated from available molecular constants of CO shows that a small correction in the vibrational constants may be necessary. A generalized treatment of optical gain on vibrational-rotational transitions is given and it is seen that it is advantageous to operate these lasers at as low a temperature as possible for production of maximum gain. An attempt is made to analyze the excitation mechanisms responsible for these laser transitions. It is seen that the excitation processes, under pulsed operation, have to be complicated and time-dependent in order to be able to duplicate theoretically the time dependence observed for the laser power output. It is shown that under the conditions of very selective excitation of a particular vibrational level, it should be possible to obtain cw laser oscillation on some $P$-branch vibrational-rotational transitions.