LABORATORY OBSERVATION OF MASER ACTION IN NH3 THROUGH COLLISIONAL COOLING

We report the observation of maser emission from the J=4, K=3 inversion transition of ammonia, 14NH3, at temperatures from 10 to 27 K. The necessary population inversion is apparently created by selective collisional energy transfer as the ammonia is cooled in collisions with cold helium atoms in a cryogenic cell. Several other inversion transitions were also observed; however, only the (4,3) line was seen in emission. When the experiment was repeated using hydrogen molecules in place of helium, maser emission was not observed for any transition. © 1995 The American Physical Society.