A cryogen-free HTS Josephson junction detector for terahertz imaging

Abstract

A cryogen-free terahertz (THz) imaging system based on a high-temperature superconducting (HTS)Josephson junction detector is reported. The detector was made of a YBa 2 Cu 3 O 7-x (YBCO) step-edge Josephson junction and integrated into an on-chip thin-film antenna. The HTS Josephson detector was cooled via a commercial mechanical cryocooler; an important step towards cryogen-free THz instrumentation, which is critical for industrial acceptance. In addition, it is shown that operating the detector in a cryocooler provides improved flexibility for optimising the detector parameters and performance due to the ability to adjust the temperature compared to liquid nitrogen cooling methods. The DC and AC characteristics, the detector responsivity and the noise-equivalent power (NEP) of the detector, and resulting image quality were studied as the function of operating temperatures.

HTS step-edge Josephson junction terahertz harmonic mixer

“…The ring-slot antenna has a truncated circular ground plane and a coplanar waveguide (CPW) feed network that attaches to a CPW lowpass filter (LPF) with a -3dB cut-off frequency of approximately 250 GHz. This ring-slot/CPW combination is similar to that used previously for amplitude detection [4], but has been adapted here for use as a harmonic mixer and its parameters optimized to give peak realized gain around 620 to 640 GHz. The LPF is connected to a tapered CPW line for efficient coupling to the bias-tee circuit, such that the width of the CPW centre conductor matches the width of the microstrip line with a characteristic impedance of 50 .…”

Experimental Investigation of a Broadband High-Temperature Superconducting Terahertz Mixer Operating at Temperatures Between 40 and 77 K

“…Furthermore, the reported measurement results did not discuss the influence of bath temperature on the mixer operation conditions and conversion performance. Based on CSIRO well-established HTS step-edge junction technology [14] and previous achievements in developing various HTS passive and active devices at high frequencies [15]- [19], we have, in this work, developed a broadband HTS Josephson-junction THz harmonic mixer. The experimental characterization results of the broadband HTS THz mixer at two THz bands (200 GHz and 600 GHz) and at bath temperature from 40 K to 77 K are presented in this paper.…”

THz Radiation Measurement with HTSC Josephson Junction Detector Matched to Planar Antenna

“…Several research groups report on sub-THz detection system based on YBCO Josephson junction detectors in a planar antenna configuration. Du et al integrated a ring-slot [12,34,43] and log-periodic [44] planar antennas with relatively low input impedance (~30 Ω) for HTSC YBCO step-edge Josephson junctions, achieving a voltage responsivity ( ) ≈ 3.5 kV • W −1 and an estimated NEP of ∼1 × 10 −12 W•Hz −1/2 at 60 K. Additional structures were presented by Nakajima et al [45] and Gao et al [46,47]. They were able to obtain planar antennas with low input impedance (~13 Ω) combined with YBCO grain-boundary Josephson Junctions detectors, using coplanar waveguide feeding.…”