Intracavity Triple Resonance Spectroscopy in CH₃OH FIR Lasers

Abstract

A very interesting aspect of FIR laser spectroscopy is its contribution to the physical insight of the laser active molecules themselves. In fact, a molecule can display several FIR laser emissions only if its spectrum is dense and extended enough so as to have high coincidence probabilities with the available pump lines (usually CO₂). This usually means serious difficulties in the spectrum assignments, since experimental and computational inaccuracies lead to very frequent ambiguous cases. On the other hand, new line assignments are a continuous challenge to further improvements in the molecular model. The use of optical pumping for the excitation of the FIR lasers allows the direct application of external CW and oscillating fields to the active medium, thus making, for instance, Stark effect and triple resonance (IR-FIR-RF) experiments possible. The study of the stark behavior of a FIR laser emission can give valuable hints for the J and K- quantum numbers involved in the laser cycle [1]. Triple resonance experiments have proved to be very important for the study of the A symmetry states of CH₂OH (2,3], the richest laser — active molecule known up to now.