Shi Shengcai

Terahertz Direct Detection Characteristics of a Superconducting NbN Bolometer

We report the terahertz direct detection characteristics of a spiral antenna coupled NbN superconducting hot-electron bolometer (HEB) at a bath temperature of 4.2K. Thermal conductance determined from resistance transition curves with different bias currents is found to be 3 x 10(-7) W/K. The device shows a read-out circuit limited noise equivalent power (NEP) of 4.5x10(-12) W/Hz(1/2) at 4.2K with a home-made transimpedance amplifier operating at room temperature.

Noise Behaviour of a THz Superconducting Hot-Electron Bolometer Mixer

A quasi-optical superconducting NbN hot-electron bolometer (HEB) mixer is measured in the frequency range of 0.5-2.5 THz for understanding of the frequency dependence of noise temperature of THz coherent detectors. It has been found that noise temperature increasing with frequency is mainly due to the coupling loss between the quasi-optical planar antenna and the superconducting HEB bridge when taking account of non-uniform distribution of high-frequency current. With the coupling loss corrected, the superconducting HEB mixer demonstrates a noise temperature nearly independent of frequency.

Extraction of material parameters of a bi-layer structure using Terahertz time-domain spectroscopy

For a bi-layer structure consisting of a film deposited on a substrate, a new extraction method is proposed using which we can extract both the material parameters of the film and the thickness of the substrate from the measured Terahertz transmission through it, so long as the complex refractive index of the substrate is known beforehand. This method is applicable to a range of refractive indices of the film less than the refractive index of the substrate and a very wide range of layer thicknesses from 20 μm to at least 200 μm. It is very useful in some cases where the thickness of the substrate cannot be determined using conventional methods such as a Vernier caliper or micrometer screw.

Terahertz detection with twin superconductor-insulator-superconductor tunnel junctions

Terahertz detection with twin superconductor–insulator–superconductor (SIS) tunnel junctions, which are connected in parallel via an inductive thin-film superconducting microstrip line, is mainly studied. Firstly, we investigate the direct-detection response of a superconducting twin-junction device by means of a Fourier transform spectrometer. Secondly, we construct a direct-detection model of twin SIS tunnel junctions. The superconducting twin-junction device is then simulated in terms of the constructed model. The simulation result is found to be in good agreement with the measured one. In addition, we observe that the direct-detection response of the device is consistent with the noise temperature behaviour.