4B4 - Rate determining processes for the production of radiation in high power molecular lasers

The excitation mechanisms and relaxation processes will be described for a closed molecular gas laser of 240 cm length and 2.3 cm diameter filled with 1 torr carbon dioxide, 2.5 torr nitrogen, and 7.2 torr helium; the influence of adding 0.2 torr water vapor is discussed. When all the four components are present, an output of 103 watts is reached with an efficiency of 12.5 percent. It will be argued that in the absence of water vapor the deactivation of the lower laser level is rate determining for the radiation production. However, the addition of water vapor (0.2 torr) contributes greatly to depopulating the lower laser level by thermal relaxation, and it makes the output increase by more than a factor of two. In the latter case the vibrational excitation of the nitrogen molecules by electron impact is rate determining. We have observed that small amounts of impurities with partial pressures, sometimes less than 10^-2torr, may cause a considerable decrease of radiation output. This "poisoning" effect, caused by very small impurity concentrations, can be avoided by using a discharge tube made from fused silica (quartz).