Modern resonator spectroscopy at SubMM wavelengths

The resonance methods of investigations are widely used in precision spectroscopy in all frequency ranges due to their high sensitivity. But the resonance systems have different specific features in each range. In the millimeter (MM) and submillimeter (SubMM) ranges, classical open Fabry-Perot resonators with an empty resonator Q-factor of about 106 (for reasonable sizes) are used for the gaseous and condensed media investigations. The present work based on the previous development is to our knowledge the first advancement of high-sensitivity classical resonator spectroscopy to frequencies of up to 520 GHz. The resonator spectrometer earlier developed at the IAP RAS, methods of measurement, and the results of studying various materials from 40 GHz up to 370 GHz are well described. So in present paper, a detailed description of the resonator excitation system and the frequency phase lock system, which were essentially modified for operation at the 350-520 GHz, is presented. Also the first results obtained using the spectrometer in the extended frequency range are reported.