The Precise Microwave Resonator Spectroscopy of Gases and Condensed Media

Abstract

Perot resonator has been elaborated and created. The sensitive element is high-Q open resonator (Q_106) and the sample is situated in it. For resonator exiting the waveguide-quasioptical supplying system has been used. Six uniform modules with the same adjusting sizes are used for working in the frequency range from 36 GHz up to 400 GHz. The backwave oscillators (BWO) stabilized by a phase lock-in loop system, with Quartz or Rubidium reference generator, were used as the source of microwaves.The principle difference apart from the known resonator spectrometers is the using for the resonator curve recording (the resonator curve width contains the information about absorption) the precise digital frequency synthesizer with fast frequency scanning (switching time 200 nsec, minimal frequency step = 0.3Hz) and without loss of phase of oscillation after switching. The fast scanning permits greatly to reduce the recording time and by this way to avoid the low frequency resonator drifts which are the main source of errors in the resonator curve width measuring. By averaging of fast scans the record accuracy of resonator curve width measuring that is + 25 Hz apart from ± 500Hz for set-ups with traditional synthesizers was reached. This accuracy corresponds to 0.002 dB/km absorption sensitivity. For the gases and condensed media (liquid, solid and metals) the original methods and software have been developed. The reached spectrometer parameters permitted to carry out the set of pioneer investigations in the three main directions:1. With the highest sensitivity at temperatures from -20C up to +30C to investigate the real atmosphere absorption as in the absorption lines and in the "transparency windows" that permits to investigate the property of continual absorption of water vapor which are essentially important for advancing both atmosphere absorption models and the theory of intermolecular interaction.2.To study the loss mechanisms in the modem dielectrics with extralow absorption (tan6-106) like CVD-Diamond and Silicon at the temperatures from room one up to 600C. It was shown that there exists the principal possibility of CVD-Diamond absorption reducing at least by 10 times.3. The satellite antenna reflectivity investigations have been made. It was revealed that the reflective coverings of composite carbon fibbers antennas have inadmissibly more reflective losses which lead to the essential noise temperature increasing of high sensitive cooled receivers. Also unexpected reflectivity behavior of reflectors at liquid Nitrogen temperatures was found. The configuration of resonator spectrometer is well described in the set of previous publications [1][2][3] including the "MSMW'2001" proceeding (Fig.5). The main feature of the new activity is the frequency range extending from low side up to 36 GHz and mainly the real advancing in SubMM range up to 400 GHz. This advancing was made with using three uniform modules with the same adjusting sizes and design like in MM range. The two SubMM modules on the base of BWO type OB-24 an...

THz radiation sensors

“…Their sensi− tivity is quite suitable to be used in mm wave spectrometers [88,90] with moderate or high resolution. In the range of n »100-120 GHz, the threshold sensitivity of SBDs can reach NEP »5×10 -12 W/Hz 1/2 [91]. In InP−based SBDs with wide− −band log−periodic toothed antenna, the sensitivity reach 10 3 V/W at n = 0.…”