THz Microscopy of Quantum Cascade Laser Radiation Using Josephson Junctions
Abstract
Josephson junctions (JJs) embedded into the feed point of a thin film antenna made from yttrium barium copper oxide (YBCO) are well suited as a miniature sensor for GHz- and THz-frequency fields. A spatially and frequency-resolved image of electromagnetic field intensity is obtained by scanning the region of interest. The sensor is read out by measuring the dc current-voltage (IV) characteristic of the JJ. Discrete frequencies together with their corresponding intensities can be extracted from measurements by evaluating the Shapiro steps in the IV domain. To extract a continuous spectrum from the IV characteristic, the numerical method of Hilbert transform spectroscopy is used and its applicability to our JJs is evaluated. As a benchmark of the setup’s capabilities, radiation from a quantum cascade laser (QCL) THz source is characterized both spectrally and spatially. A frequency comb spectrum consistent with the QCL’s cavity is revealed by Hilbert transform spectroscopy. The far field radiation patterns of two strong QCL modes are resolved individually and show different characteristics. Optical QCL feedback is observed when the sensor is brought in close proximity.
Details
- External Organisation(s)
-
Technische Universität Braunschweig
ETH Zurich
- Type
- Article
- Journal
- IEEE Transactions on Applied Superconductivity
- Volume
- 36
- ISSN
- 1051-8223
- Publication date
- 12.01.2026
- Publication status
- E-pub ahead of print
- Peer reviewed
- Yes
- ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials, Condensed Matter Physics, Electrical and Electronic Engineering
- Electronic version(s)
-
https://doi.org/10.1109/tasc.2026.3652510 (Access:
Closed
)
