Influence of diffusion on the saturation of gain in gaseous active media

An analysis is made of the effect of the diffusion of excited particles in an active medium on the characteristics of the saturation of the gain and output power in the case of gas lasers. It is shown that the diffusion increases the effective zone of the interaction between the active medium and the radiation field. To a high accuracy, the influence of the diffusion on gain saturation can be allowed for by introducing an effective saturation parameter which is governed by the characteristics of the medium and by the geometry of the system. In a more detailed consideration an allowance has to be made for the distortion of the saturation characteristics, which is strongest in the case when the diffusion length is comparable with the transverse size of a light beam. The values of the saturation parameter calculated from the relationships derived in the present paper are in agreement with the published experimental results.