Using a continuous tunable CO2-laser system for optical pumping a far-infrared laser we investi- gated the four ammonia gas isotopes 14NH3, 151TH3, 14ND3and 15ND3. We found laser emissionvia stimulated Raman scattering at about 300 molecular transitions in the region from 15 cm-1to more than 200 cm-1, about 250 of them observed for the first time. Thereby photon conversioncoefficients of up to 12 % and tuning intervals exceeding 3 cm-1 have been accieved.
"OPFIRL investigation of ammonia", Proc. SPIE 2104, 18th International Conference on Infrared and Millimeter Waves, 21041W (30 August 1993); doi: 10.1117/12.2298500; https://doi.org/10.1117/12.2298500