Pressure effects on the frequency of continuous-wave optically pumped far-infrared lasers

The frequency of the 170.6-microm cw CH(3)OH optically pumped laser emission has been remeasured at different pressures without observing the pressure shift observed by Lawandy and Koepf [Opt. Lett. 5, 383 (1980)]. The far-infrared frequency was synthesized with two stabilized CO(2) lasers. No measurable pressure shift over the operating pressure range of the laser was observed, and the frequency was confirmed to be 1 757 526.3 MHz. However, competing lasing lines were found to produce spurious effects on the frequency. These effects may explain the apparent shifts.