Laser-pumped molecular lasers - Part II: Submillimeter laser experiments

We report the first experimental determination of the gain spectrum of a laser-pumped submillimeter laser amplifier. Single-mode pump and submillimeter oscillators were used to determine the gain as a function of submillimeter laser frequency, pump intensity, relative polarization, and molecular gas pressure. The 385 μm transition in D
2
O and the 496 μm transition in CH
3
F, both pumped by a CO
2
laser, were investigated. The use of single-mode lasers allows a direct comparison with theory. Good agreement is obtained with our recent theory which takes into account two photon contributions to the gain as well as space orientation (
M
-level) molecular degeneracy.