It may be possible to construct a new class of FIR gas lasers based on IR optical pumping of perturbation-allowed FIR transitions. They would be restricted to neither the low pressures required for OPFIR laser operation nor to the dearth of molecules with the chemical robustness required for discharge- pumped perturbation lasers. Salient features, including potential increases in laser efficiency, are presented and several candidate systems are discussed.
David D. Skatrud,
"Optically pumped FIR perturbation laser", Proc. SPIE 1514, 15th International Conference on Infrared and Millimeter Waves, 15144Z (1 December 1990); doi: 10.1117/12.2301589; https://doi.org/10.1117/12.2301589