Theoretical calculation on the output power density of optically pumped far-infrared laser was usually based on three-level system model for simplicity. Considering on the far-infrared self-absorption effect of the operating gas medium, the ready-made calculation should be renewed. The calculating method of self-absorption was proposed.
"Self-absorption revision for the theory of OPFIRL", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15764K (1 October 1991); doi: 10.1117/12.2297877; https://doi.org/10.1117/12.2297877