Investigation of cathodes for use in gas lasers

The problems facing the developer of laser cathodes are complex. Unlike vacuum emission, not only must the intrinsic properties of the cathode be considered but gas-surface reactions, sputtering, and the role played by cathode-plasma reactions must all be taken into consideration. The most difficult problem for dc gas lasers is that of obtaining adequately reliable cathodes. In general, when chemically nonreactive gases such as He, Ne, Xe, Ar, etc., are used we have found that some form of structure which constraints BaSrO as the emitter will more than adequately supply the current required. Thermionic hollow cathode structures which will be described have been found particularly advantageous, giving up to 100 amperes, even under adverse conditions. When reactive gases such as O2, CO2or H2O are used a thermionic cathode containing BaZrO3has been found to be a good emitter with long life. This cathode is unique in that it emits better in an oxidizing atmosphere than it does in a nonreactive ambient.