Millimeter-wave Hilbert-transform spectroscopy with high-<i>T</i> <i>c</i> Josephson junctions

Abstract

The application of Hilbert-transform spectroscopy for the measurement of high-harmonic content of the radiation from a frequency multiplier has been demonstrated in the spectral range from 60 to 450 GHz. YBa2Cu3O7−x grain-boundary Josephson junctions made on (110) NdGaO3 bicrystal substrates have been used in these experiments. The internal Josephson radiation of the junctions reveals a Lorentzian shape due to thermal noise broadening. The possibility to obtain a spectral resolution as low as 280 MHz (∼0.01 cm −1) has been shown with a Josephson junction operating at liquid-nitrogen temperature.