Heterodyne of Optically Pumped FIR Molecular Lasers and Direct Frequency Measurements of New Lines

Direct frequency measurements of optically pumped far infrared (FIR) molecular lasers are reported, also for new lines. This heterodyne technique is versatile and simple. By controlling some parameters of resonator and pump source, possible causes of error are evidenced in the precise frequency determination. The implications for molecular spectroscopy are also discussed.