Knowledge Bank

We have measured 12 far-infrared laser frequencies of optically pumped CH3OH, 6 of which are new lines. The frequencies range from 2.8 to 11.4 THz, with ten lines having frequencies higher than 7 THz. Two frequency stabilized $CO2$ lasers were used as standards for the heterodyne measurements. The frequency of the $26.4 \mum line at 11.4 THz is the highest ever measured with this technique. The lines were generated in a high-frequency far-infrared Fabry-Perot laser cavity pumped by a $CO2$ laser. The cavity has a high Q for wavelengths below $150\backslash mum$, and uses variable coupling to optimize the cavity for each line.