Josephson Spectrometer with Waveguide Coupling for Liquid Identification

Fast and reliable liquid identification is possible, in principle, by Josephson spectroscopy at subterahertz and terahertz ranges, but high speed of measurements, extended frequency range and high accuracy of intensity measurements are required. Quasioptical radiation coupling used in our previous demonstrators of the identifier can not be used at low frequencies where diffraction losses increase drastically. In this paper, we describe a new spectrometer based on a frequency-selective high-Tc Josephson detector with dielectric waveguide coupling and consider its frequency scanning speed limit at a given accuracy of power measurement. According to our estimations, frequency scanning speed up to 1.3 THz/sec can be achieved if spectral resolution and power measurement error are 3 GHz and 0.1%, respectively. We have developed new compact radiation coupling system based on dielectric waveguides, which extends low frequency limit of our spectrometer down to 1.75 GHz. Small spread of angles of incidence of radiation and polarization control allow to recover the dielectric constants of the substance under test in a more simple way than in the case of quasioptical coupling. The results of first measurements with the new radiation coupling will be presented in our paper.