Precise Pump and Emission Wavelengths for New CH OH Laser Lines

Abstract

The importance of methyl alcohol in submillimeter (SMM) laser research is well know. It was one of the first molecules to be used for SMM generation via optical pumping with a CW CO 2 laser [1], and has been one of the most fertile up to now, generating radiation in the wavelength ∼ 40μm to ∼ 1200μm [2]. Some of the basic reasons for its success are the excellent overlap between the C-O strech mode and the CO 2 laser spectrum. The complexity of the torsional-rotational spectrum, the liberal selection rules caused by the asymmetry of the molecule and the large dipole moments associated with as well the internal as the overall rotation. Therefore, good spectroscopic data for CH 3 OH, particularly on the rotational structure of excited vibrational states, is essential for better understanding the laser emission. Inversely, assignments of the SMM laser emission can serve as a basis for modeling this molecule. Work in this direction has been published lately [3-5], but the experimental basis has still to be expanded to gain a clear understanding of the vibrationally excited CH 3 OH molecule. For this purpose, the CO 2 -TEA laser seems a suitable pumping source: the possibility of off-resonance pumping and its broad linewidth which increases the chances of coincidences with molecular absorption lines should lead to many new SMM laser emissions. However, initial results [6-7] have been disappointing since only 3 new SMM lines were discovered but better spectral matching between the CO 2 -TEA laser and the CH 3 OH absorption line [8] improved these performances. We now report the measurements of many new SMM laser lines in CH 3 OH via optical pumping by a CO 2 -TEA laser. Some of these originate from pump transitions for which SMM emission has not previously been observed.