TY - JOUR

T1 - Dual Frequency Mixing Products and Terahertz Hilbert-Transform Spectroscopy with Josephson Cantilevers in a THz Microscope

AU - Tollkuhn, Marco

AU - Elenskiy, Ilya

AU - Hampel, Benedikt

AU - Schilling, Meinhard

N1 - Funding Information: Manuscript received December 20, 2019; revised July 8, 2020; accepted July 9, 2020. Date of publication July 14, 2020; date of current version July 27, 2020. This work was supported in part by the Braunschweig International Graduate School of Metrology - B-IGSM, in part by the DFG Research Training Group GrK 1952/2 “Metrology for Complex Nanosystems,” in part by the Laboratory for Emerging Nanometrology - LENA, and in part by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy - EXC-2123 QuantumFrontiers - 390837967. This article was recommended by Associate Editor S. Berggren. (Corresponding author: Marco Tollkühn.) The authors are with the Institut für Elektrische Messtechnik und Grund-lagen der Elektrotechnik, TU Braunschweig, 38106 Braunschweig, Germany (e-mail: m.tollkuehn@tu-bs.de; i.elenskiy@tu-bs.de; b.hampel@tu-bs.de; m.schilling@tu-bs.de).

PY - 2020/7/14

Y1 - 2020/7/14

N2 - Josephson cantilevers, based on high-temperature superconducting yttrium barium copper oxide Josephson junctions, can be employed for the measurement of frequency and power of microwave and terahertz radiation. Each Josephson cantilever carries at least one Josephson junction with a dedicated antenna structure for better coupling. In the THz microscope, such cantilevers are employed for spatially resolved measurements of radiation distributions over either active emitting or passive samples that are irradiated by an external terahertz source. The power distribution can be reconstructed from Shapiro steps in the current-voltage characteristic of the cantilever's Josephson junction by methods including Hilbert spectroscopy. We show that simulations with simultaneous excitation with more than a single frequency result in the appearance of Shapiro steps at sum and difference frequencies. The amplitudes of these steps approximately follow Bessel functions, as with the Shapiro steps from single frequency excitation. This is confirmed by a setup in the THz microscope, where the Josephson cantilever is simultaneously subjected to 40 GHz radiation of variable power and 693 or 762 GHz radiation from a far-infrared laser system. Josephson mixing spectra show peaks at sum and difference frequencies following Bessel curves with increasing power, as it was predicted for the according Shapiro steps. These products should be avoided for a reconstruction of the original signals by Hilbert spectroscopy.

AB - Josephson cantilevers, based on high-temperature superconducting yttrium barium copper oxide Josephson junctions, can be employed for the measurement of frequency and power of microwave and terahertz radiation. Each Josephson cantilever carries at least one Josephson junction with a dedicated antenna structure for better coupling. In the THz microscope, such cantilevers are employed for spatially resolved measurements of radiation distributions over either active emitting or passive samples that are irradiated by an external terahertz source. The power distribution can be reconstructed from Shapiro steps in the current-voltage characteristic of the cantilever's Josephson junction by methods including Hilbert spectroscopy. We show that simulations with simultaneous excitation with more than a single frequency result in the appearance of Shapiro steps at sum and difference frequencies. The amplitudes of these steps approximately follow Bessel functions, as with the Shapiro steps from single frequency excitation. This is confirmed by a setup in the THz microscope, where the Josephson cantilever is simultaneously subjected to 40 GHz radiation of variable power and 693 or 762 GHz radiation from a far-infrared laser system. Josephson mixing spectra show peaks at sum and difference frequencies following Bessel curves with increasing power, as it was predicted for the according Shapiro steps. These products should be avoided for a reconstruction of the original signals by Hilbert spectroscopy.

KW - High-temperature superconductor (HTS)

KW - Hilbert spectroscopy

KW - Josephson cantilever

KW - mixer

KW - THz microscopy

KW - yttrium barium copper oxide (YBCO)

UR - http://www.scopus.com/inward/record.url?scp=85089304164&partnerID=8YFLogxK

U2 - 10.1109/tasc.2020.3008969

DO - 10.1109/tasc.2020.3008969

M3 - Article

AN - SCOPUS:85089304164

VL - 30

JO - IEEE Transactions on Applied Superconductivity

JF - IEEE Transactions on Applied Superconductivity

SN - 1051-8223

IS - 7

M1 - 9140345

ER -