Abstract In recent years, 3D Dirac semimetals (DSM) with linear energy‐momentum dispersion near the Fermi points have emerged as promising material candidates for novel tunable metamaterial devices due to their prominent electromagnetic performance and excellent tunability. In this work, the propagation characteristics of 3D DSM‐supported double and triple stripe patterned metamaterial absorbers (MMAs) are investigated in the terahertz (THz) regime by facile modulation of the Fermi level. The results manifest that for the double stripe patterned devices, two strong absorption peaks with near unity are observed at 0.97 THz and 1.63 THz, respectively. When the Fermi level varies in the range of 0.01–0.15 eV, the amplitude (frequency) modulation depth of resonance is up to 77% (27.3%). Additionally, triple stripe MMAs supported by 3D DSM are devised, which can achieve resonant absorption peaks at three specific frequencies of 0.23, 0.345, and 0.46 THz, while the amplitudes of the peaks are as high as 0.997, 0.940, and 0.779, respectively. Furthermore, the resonances can also be regulated, and the amplitude MD reaches ≈20%. These results are very helpful in understanding the tuning mechanisms of metamaterial devices and aiding the design of THz functional devices, such as receivers, detectors, and modulators. 

3D Dirac Semimetal Supported Tunable Multi‐Frequency Terahertz Metamaterial Absorbers

We combine parametric frequency upconversion with the single-photon counting technology to achieve terahertz (THz) detection sensitivity down to the zeptojoule (zJ) pulse energy level. Our detection scheme employs a near-infrared ultrafast source, a GaP nonlinear crystal, optical filters, and a single-photon avalanche diode. This configuration is able to resolve 1.4 zJ (1.4 × 10-21 J) THz pulse energy, corresponding to 1.5 photons per pulse, when the signal is averaged within only 1 s (or 50,000 pulses). A single THz pulse can also be detected when its energy is above 1185 zJ. These numbers correspond to the noise-equivalent power and THz-to-NIR photon detection efficiency of 1.3 × 10-16 W/Hz1/2 and 5.8 × 10-2%, respectively. To test our scheme, we perform spectroscopy of the water vapor between 1 and 3.7 THz and obtain results that are in agreement with those acquired with a standard electro-optic sampling (EOS) method. Our technique provides a 0.2 THz spectral resolution offering a fast alternative to EOS THz detection for monitoring specific spectral components in spectroscopy, imaging, and communication applications.

Zeptojoule detection of terahertz pulses by parametric frequency upconversion.

The field of terahertz (THz) science and technology research area have been exponentially growing recently, motivated by the increasing demand for safer security imaging, better quality control within manufacturing industries, space and astronomical investigation, biomedical diagnostics, and larger communication bandwidth. The THz waves detection mechanism is one of the critical components in developing a high efficiency and high sensitivity THz communication system. This paper reviews the principle and instrumentation of THz optical metrology for the precise and accurate characterization of THz detectors in the range of 0.1 THz to several THz. In this context, we individually discuss the determination of radiation input power and effective area followed by a survey of THz optical measurement methodology used in the state-of-the-art THz detectors. In addition, challenging issues remaining in the THz detector measurements are provided. This paper sets out a guideline to address the main concept behind the THz detector measurement as well as their challenges and opportunities. Additionally, useful insight is given through a summary of available power meter instrumentation for THz input power calibration. 

Input Power and Effective Area in Terahertz Detector Measurement: A Review

A new type of traveling wave antenna is presented. Key features of the antenna are planar, low mass and wide bandwidth of operation. One such antenna was designed for terahertz radiation detection and realized in standard IBM CMOS-SOI process with subsequent MEMS post processing. Measurements performed at 655GHz showed very good agreement with the theoretical predictions based on full wave simulations. The present article describes the antenna physics, design, fabrication and measurement results.

/pdf/wideband-planar-skirt-antenna-and-its-application-for-the-4bhn765iyp.pdf

Wideband planar skirt antenna and its application for the detection of terahertz radiation

The field of terahertz (THz) science and technology research area have been exponentially growing recently, motivated by the increasing demand for safer security imaging, better quality control within manufacturing industries, space and astronomical investigation, biomedical diagnostics, and larger communication bandwidth. The THz waves detection mechanism is one of the critical components in developing a high efficiency and high sensitivity THz communication system. This paper reviews the principle and instrumentation of THz optical metrology for the precise and accurate characterization of THz detectors in the range of 0.1 THz to several THz. In this context, we individually discuss the determination of radiation input power and effective area followed by a survey of THz optical measurement methodology used in the state-of-the-art THz detectors. In addition, challenging issues remaining in the THz detector measurements are provided. This paper sets out a guideline to address the main concept behind the THz detector measurement as well as their challenges and opportunities. Additionally, useful insight is given through a summary of available power meter instrumentation for THz input power calibration.

Terahertz superconducting kinetic inductance detectors demonstrating photon-noise-limited performance and intrinsic generation-recombination noise

Niobium nitride (NbN) superconducting tunnel junctions (STJs) have an energy gap nearly double that of niobium STJs, making them potential sensitive detectors that operate at higher frequencies and temperatures. In this paper, we investigate the direct-detection behavior (i.e. the spectral response, current responsivity, noise characteristics, and noise equivalent power (NEP)) of a 500 GHz NbN STJ detector at temperatures from approximately 5 to 9 K. The detector shows an uncorrected NEP of 3.8 x 10(-13) W/root Hz around 5 K and 1.5 x 10(-12) W/root Hz at 9 K. Its performance can be further improved by adopting a cryogenically cooled readout circuit and fabricating the device with a wiring layer of higher critical-transition temperatures.

Terahertz direct-detection behavior of niobium nitride superconducting tunnel junctions above liquid helium temperature

Microwave Kinetic Inductance Detectors (MKID) are a promising low temperature superconducting detector because of high sensitivity, easy frequency-domain multiplexing and simple structure for large-format arrays. To develop large-format THz detectors for China’s Antarctic THz telescope, we have preliminarily designed an aluminum 64-pixel MKID array operating at the 350 GHz band. In this paper, the characteristics of the MKID array are thoroughly measured.

Characterization of a 0.35 THz aluminum 64-pixel MKID array

High-Performance Ti Transition-Edge Sensor-based Photon-Number Resolving Detectors

Superconducting planar-transmission-line resonators play an increasingly important role in applications such as astronomical detection and circuit quantum electrodynamics. When measuring the transmission response of an array of resonators, however, one often observes some spurious resonances besides the intrinsic ones. In this letter, the effect of the cavity accommodating a half-wavelength superconducting microstrip resonator is investigated. An attenuation pole associated with the intrinsic resonance of the half-wavelength resonator is clearly observed and found to be resulted from the mutual coupling between the microstrip resonator and the cavity. In addition, it is demonstrated that adding a superconducting ground layer for such a microstrip resonator can avoid the frequency shift owing to an ever-present thin air gap between the microstrip resonator and the cavity and can also improve the Q factor of the microstrip resonator.

Cavity and ground effects on a superconducting microstrip resonator

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