Phenomenological approach to the design of highly tunable pressure-broadened gas lasers

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Abstract
Recently published measurements of the gain in continuous‐wave CO2 waveguide lasers have indicated that the small‐signal gain decreases exponentially with pressure in the range beyond about 70 Torr. In the present paper, the observed dependence of the gain on pressure has been incorporated into the general theory of homogeneously broadened gas lasers to form a phenomenological model of the waveguide laser. The model is then used to generate a series of curves intended to aid in the selection of gas mixture, operating pressure, discharge length, and mirror reflectivities when tunability is the primary design goal. The operating parameters are chosen on the basis of the desired laser characteristics (bandwidth and output power) and a small number of molecular parameters. Although the discussion emphasizes CO2 waveguide systems, the design curves are applicable to all homogeneously broadened gas lasers. It is found that, although there exists a critical pressure beyond which the laser should not be operated for reasons of efficiency, the tunability can be increased indefinitely by incorporating a longer discharge and an appropriate tunable internal etalon.

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