Submillimeter backward-wave tube frequency-locked to an HCOOH laser for use in a submillimeter spectrometer

The emission frequency of a backward-wave tube (BWT) was locked to the emission frequency of an optically pumped HCOOH laser (λ = 716.157 GHz) characterized by a free-running stability of ~ 10^– 10 in 1 s. The experimental results demonstrated that without recourse to phase locking the spectral width of the emission line of the BWT was ~ 200 kHz, whereas locking to the laser oscillations reduced the emission spectrum to hundreds of hertz. A brief discussion is given of the design of a spectrometer based on the use of phase locking of a BWT to a laser and of a tunable microwave synthesizer. Preliminary results of an investigation of such a system are reported.