Modern millimeter-wave resonator spectroscopy of broad lines

Broad line millimeter-wave resonator spectroscopy is shown to have high sen sitivity and fast and broad frequency scanning possibilities. Methods of ab solute measurement of separate line, sample, and resonator losses are demon strated and discussed. The primary radiation source (BWO) frequency is cont rolled digitally with minimal steps of a few hertz and switching time of 20 0 ns. An open Fabry-Perot resonator with a quality factor of similar to 600 000 is used. A resonance-width measurement accuracy of 20 Hz is reached wh ich corresponds to an absorption coefficient sensitivity Limit of similar t o 4 x 10(-9) cm(-1) (0.0018 dB/km). In situ open atmosphere spectra records at 44-98 and 113-200 GHz are obtained in one experiment each. Lines of atm ospheric oxygen and atmospheric water are observed. The water line at 183 G Hz fits the Van Vleck-Weisskopf shape up to 20 half-widths from the line ce nter within experimental accuracy. The dry-air broadening parameter for thi s water line is defined as 3.985(40) MHz/Torr. Atmosphere absorption in a 1 40-GHz window is measured. Results from other authors are compared. Possibl e. applications of the modern broad line millimeter-wave resonator spectros copy including real-lime monitoring of open-air atmosphere and technologica l processes and measurement of absorption in thin dielectric films and cond ucting surfaces and metals are discussed, (C) 2000 Academic Press.