Triple resonance on the CH3OH laser: Asymmetry splittings and new lines

In the optically pumped far-infrared (FIR) laser an oscillating field can be applied directly on the laser medium. A resonance between a tunable RF field and any transition connected to one of the levels of the laser cycle will be detected as a change in the output power. Fig. 1 shows the three possible cases. Transition 1 decreases the output power, which is on the contrary, increased by transitions 2 and 3, even if the signal is smaller in these latter cases. Such an experiment is more conveniently referred to as a triple resonance (TR) experiment because of the simultaneous presence of three coherent radiation fields. The feasibility of TR was demonstrated in HCOOH (1) and CH3OH (2,3) FIR lasers.