Terahertz spectral analysis by ac Josephson effect in high-Tc bicrystal junctions

A prototype of a terahertz Hilbert-transform spectrum analyzer based on a high-T_c Josephson junction integrated into a Stirling cooler has been developed. The detector response of YBa₂ Cu₃O_7-x Josephson grain-boundary junctions to monochromatic radiation with the frequency f in the range from 60 GHz to 5 THz has been studied. Odd-symmetric resonances near the voltages V=hf/2e in the responses ΔI(V) of these junctions to radiation with different frequencies f have been observed in a decade of spectral range for any operating temperature between 30 to 85 K. Decreasing the junction temperature from 85 to 30 K by a Stirling cooler, the spectral analysis could be made in two decades of spectral range. A resolving power δf/f~10^-3 has been shown in the terahertz spectral analysis with the low-resistive Josephson junctions. As an example of application of this analyzer, an optimization of the single-line operation of a far-infrared optically-pumped CH₃OH laser has been demonstrated