Frequency Measurement of Far-Infrared Laser Emissions Generated by C-13 Methanol Isotopologues

The C-13 methanol isotopologues
¹³
CH
₃
OH,
¹³
CD
₃
OD, and
¹³
CHD
₂
OH have individually served as the laser medium for an optically pumped molecular laser system used to generate far-infrared radiation. Once detected the frequencies of these laser emissions were measured using a heterodyne technique to a one-sigma fractional uncertainty no less than ± 5 parts in 10
⁷
. In total, 60 far-infrared laser frequencies, ranging from 0.355 to 2.817 THz, have been measured for the first time. One of these laser emissions was discovered during this investigation and is reported with its polarization with respect to the CO
₂
pump laser, output power, and optimal operating pressure. In several cases, these measured laser frequencies are in excellent agreement with the calculated values, as determined through combination-loop relations, further confirming the proposed spectroscopic assignments.