Gain saturation and diffusion in CO2lasers

The effect of rotational-vibrational relaxation and molecular diffusion on the saturation parameter of the CO2laser is investigated experimentally. A summary is presented of how the theory of a two-level system can be extended to a multilevel laser system like the CO2laser. Published experimental results for the rate of relaxation of the upper levels are such as to suggest that diffusion effects can play an important role in laser beams with radii of less than a few millimeters. For experimental verification of the diffusion hypothesis, the gain of a sealed CO2amplifier is measured as a function of input power for four different beam radii. The equivalent saturation parameter derived from these measurements decreases monotonically from 97 to 25 W/cm²as the average input beam radius increases from 0.9 to 2.5 mm in the 9-mm-radius discharge tube of the amplifier.