Modern millimeter-wave resonator spectroscopy of broad lines

Highly sensitive spectroscopy of molecular spectral lines under up to atmosphere and higher pressures is commonly associated with measurement of quality factor of resonator filled by studied gas. In this case the radiation absorption in spectral line can be determined from comparative measurement of resonance respond width of the loaded and empty resonator. Sensitivity of the method directly depends on the absolute value of the resonator quality factor as well as on accuracy of the resonance width measurements. Millimeter-wave resonator spectrometer having up-to-date highest sensitivity and broadest scanning ability has been developed. Main components of our resonator spectrometer are: fast sweeping (frequency switching time is 200 ns without phase jump) computer controlled millimeter-wave synthesizer based on a broad band backward-wave oscillator, Fabry-Perot resonator with quality factor of about 600,000 and resonance shape processing software. The combination of high power fast sweeping phase locked radiation source with resonator having highest possible for cavity with non-cooled mirrors quality factor gave in result parameters of the spectrometer exceeding parameters of other known analogs in more than order of magnitude. Resonance width measurement accuracy 20 Hz was reached which corresponds to radiation absorption coefficient sensitivity limit of the spectrometer of 4.10/sup -9/cm/sup -1/ or 0.0018 dB/km.