Terahertz Hilbert-transform spectral analysis with high-Tc Josephson junctions: first applications

Our recent results on Hilbert-transform spectral analysis based on ac Josephson effect are reported. High-quality epitaxial YBa 2 Cu 3 O 7-x thin-film Josephson junctions have been fabricated on untwinned (110) NdGaO 3 bicrystal substrates to satisfy the operational requirements of Hilbert-transform technique. The design and characteristics of the developed laboratory Hilbert-transform spectrometers are presented. Spectra of Josephson radiation in high-T c junctions have been measured in the frequency range from 60 to 2250 GHz, and a Lorentzian shape of Josephson radiation has been obtained both for equilibrium (eV very much less than kT) and nonequilibrium (eV very much greater than kT) cases. The first spectral measurements of coherent transition radiation at Test Facility Linear Accelerator at the Deutsches Elektronen-Synchrotron DESY (Hamburg) have been made and the length of electron bunches of 1.2 ps has been determined from these spectra. The comparison of Hilbert-transform spectral analysis with conventional techniques is presented.