Abstract-Electric and Magnetic Hotspots via Hollow InSb Microspheres for Enhanced Terahertz Spectroscopy

Mahdiyeh Sadrara,  MirFaez Miri

https://www.nature.com/articles/s41598-018-35833-2

We study electric and magnetic hotspots in the gap between hollow InSb microspheres forming dimers and trimers. The outer radius, core volume fraction, distance, and temperature of the microspheres can be chosen to achieve field enhancement at a certain frequency corresponding to the transition between energy levels of a molecule placed in the gap. For example, utilizing 80 μm radius spheres at a gap of 2 μm held at a temperature of 295 K, allow electric field intensity enhancements of 10–2880 and magnetic field intensity enhancements of 3–61 in the frequency window 0.35–1.50 THz. The core volume fraction and the ambient temperature affect the enhancements, particularly in the frequency window 1.5–2 THz. Electric and magnetic hotspots are promising for THz absorption and circular dichroism spectroscopy.

Abstract-High-Harmonic and Terahertz Spectroscopy (HATS): Methods and Applications

Yindong Huang, Chao Chang , Jianmin Yuan, Zengxiu Zhao

https://www.mdpi.com/2076-3417/9/5/853

Electrons driven from atom or molecule by intense dual-color laser fields can coherently radiate high harmonics from extreme ultraviolet to soft X-ray, as well as an intense terahertz (THz) wave from millimeter to sub-millimeter wavelength. The joint measurement of high-harmonic and terahertz spectroscopy (HATS) was established and further developed as a unique tool for monitoring electron dynamics of argon from picoseconds to attoseconds and for studying the molecular structures of nitrogen. More insights on the rescattering process could be gained by correlating the fast and slow electron motions via observing and manipulating the HATS from atoms and molecules. We also propose the potential investigations of HATS of polar molecules, and solid and liquid sources.

Printed radar technology

KIT research laboratory will develop digital manufacturing technologies for terahertz microelectronics -- funding by BMBF

KARLSRUHER INSTITUT FÜR TECHNOLOGIE (KIT)

The KIT Research Laboratory develops new assembly and connection techniques for highest-frequency electronics CREDIT Joachim Hebeler, KIT

https://www.eurekalert.org/multimedia/pub/194103.php

Parking a car with the help of radar sensors already is commonplace. Many other applications of radar technology are obvious, such as precise distance and environment sensors for robots and machines in the industrial automation sector or high-performance transmitters and receivers in telecommunications. Concrete application scenarios, however, are highly individual, the number of pieces is small, and manufacturing costs are very high. This is the point of departure of the new DiFeMiS Research Laboratory at Karlsruhe Institute of Technology (KIT). It is to develop print technologies for individual, small, and inexpensive high-frequency systems up to the terahertz range (THz). The Laboratory is funded by the Federal Ministry of Education and Research (BMBF) with about EUR 3.37 million.

When thinking of electronics, we mostly think of components on a green circuit board. But this carrier of electric components is suited for circuits working at frequencies far below 100 GHz only. At higher frequencies, boards are mainly produced by lithographic processes optimized for mass production. For medium batches of up to 10,000 products typically produced by small and medium-sized enterprises (SME), fabrication of an exposure mask for lithography is too expensive. Latest additive processes and precision printing technology might close this gap between individual and mass production.

"The core component of the planned Research Laboratory is a configurable, micrometer-precise printing platform for future highly flexible and inexpensive packaging," says Professor Thomas Zwick, who heads KIT's Institute of Radio Frequency Engineering and Electronics. Packaging or assembly and connection technology refers to all microchip-supporting components on a circuit board, from the conducting wire to the antenna. Packaging largely depends on the application, as far as the size and orientation of antennas are concerned, for instance. Hence, mass-produced off-the-shelf solutions are hardly suited. "At very high frequencies up to the terahertz range, radar technology is suited for many applications, as the high frequency enables increased measurement accuracy, higher data transmission rates, and further miniaturization."

The Research Laboratory at KIT combines systems for additive and mask-less deposition and structuring methods in a flexible printing platform. Special measurement systems can be applied to determine the frequency behavior of components and systems at more than 500 GHz. To print electric circuits, several methods are available. Here, materials with various electric properties are applied as inks. These methods are two-dimensional, such ink-jet and aerosol-jet printing, or three-dimensional, such as laser lithography. For circuits above a frequency of 100 GHz, resolution has to be increased and complementary properties have to be combined. The big challenge lies in the exact positioning of components. For this purpose, printing processes are to be adjusted with micrometer precision, such that optimum collaboration of components from different printers is ensured and circuits are kept as small as possible.

SME might use digital manufacturing processes for inexpensive assembly and connection techniques at frequencies above 100 GHz in order to develop a large number of sensor applications for Industry 4.0 and robotics. Here, many measurement tasks have to be carried out, from simple distance measurements to complex imaging. Thanks to their good resolution, high accuracy, small size, and high robustness, high-frequency sensors are particularly suited for this purpose. Moreover, emitters and receivers based on high-frequency systems might be applied in telecommunications. Digital manufacturing might enable customized, integrated, and inexpensive production.

At KIT's Research Laboratory, three research groups of Professors Thomas Zwick, Ulrich Lemmer, and Christian Koos from the Institute of Radio Frequency Engineering and Electronics, Light Technology Institute, and Institute of Photonics and Quantum Electronics are involved in DiFeMiS (German acronym of digital manufacture of THz microelectronics systems). The newly established chair of Ahmet Cagri Ulusoy at the Institute of Radio Frequency Engineering and Electronics is to join the project in the near future. The Laboratory will be funded by the Federal Ministry of Education and Research (BMBF) under the program "Microelectronics Research Laboratories in Germany" with EUR 3.37 million for a period of three years. Investments in most modern devices and facilities are to enable research on top international level. The twelve laboratories to be established under this program will open up new areas of research for future microelectronics and be used for training young scientists.

At today's kick-off event, Thomas Rachel, Parliamentary State Secretary with the BMBF, underscored the importance of the research laboratories as an investment in the future. "We want to continue to live a self-determined life in a rapidly changing world. For this, Germany and Europe need to have a strong technological basis. The 'Microelectronics Research Laboratories in Germany' provide an essential contribution. At these laboratories, electronics for the next decades will be developed to maturity and new ideas and know-how will be transferred very quickly to everyday use."

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Press contact: Kosta Schinarakis, Redakteur/Pressereferent, Tel.: +49 721 608-41956, Fax: +49 721 608-43568, E-Mail: schinarakis@kit.edu

Abstract-Multiplexing THz Vortex Beams With a Single Diffractive 3-D Printed Len

Federico Machado, Przemysław Zagrajek, Vicente Ferrando, Juan A. Monsoriu, Walter D. Furlan

https://ieeexplore.ieee.org/document/8550797

We present a novel method for experimentally generating multiplexed THz vortex beams by using a single three-dimensional printed element that combines a set of radially distributed spiral phase plates, and a binary focusing Fresnel lens. With this element, we have experimentally demonstrated that THz multiplexing can be tailored to fit within a small space on an optical bench. Results are presented beside numerical simulations, demonstrating the robust nature of the experimental method.

Abstract-Terahertz oscilloscope for recording time information of ultrashort electron beams

Lingrong Zhao, Zhe Wang, Heng Tang, Rui Wang, Yun Cheng, Chao Lu, Tao Jiang, Pengfei Zhu, Long Hu, Wei Song, Huida Wang, Jiaqi Qiu, Roman Kostin, Chunguang Jing, Sergey Antipov, Peng Wang, Jia Qi, Ya Cheng, Dao Xiang, and Jie Zhang

https://journals.aps.org/prl/accepted/d407dY16M5819b51b9d98708b359b7042e3e658c9

We propose and demonstrate a Terahertz (THz) oscilloscope for recording time information of an ultrashort electron beam. By injecting a laser-driven THz pulse with circular polarization into a dielectric tube, the electron beam is swept helically such that the time information is uniformly encoded into the angular distribution that allows one to characterize both the temporal profile and timing jitter of an electron beam. The dynamic range of the measurement in such a configuration is significantly increased compared to deflection with a linearly polarized THz pulse. With this THz oscilloscope, nearly 50-fold longitudinal compression of a relativistic electron beam to about 15 fs (rms) is directly visualized with its arrival time determined with 3 fs accuracy. This technique bridges the gap between streaking of photoelectrons with optical lasers and deflection of relativistic electron beams with radio-frequency deflectors, and should have wide applications in many ultrashort electron beam based facilities.

Abstract-Calculated Terahertz Spectra of Glycine Oligopeptide Solutions Confined in Carbon Nanotubes

Dongxiong Ling, Mingkun Zhang, Jianxun Song, Dongshan Wei

https://www.mdpi.com/2073-4360/11/2/385/htm

To reduce the intense terahertz (THz) wave absorption of water and increase the signal-to-noise ratio, the THz spectroscopy detection of biomolecules usually operates using the nanofluidic channel technologies in practice. The effects of confinement due to the existence of nanofluidic channels on the conformation and dynamics of biomolecules are well known. However, studies of confinement effects on the THz spectra of biomolecules are still not clear. In this work, extensive all-atom molecular dynamics simulations are performed to investigate the THz spectra of the glycine oligopeptide solutions in free and confined environments. THz spectra of the oligopeptide solutions confined in carbon nanotubes (CNTs) with different radii are calculated and compared. Results indicate that with the increase of the degree of confinement (the reverse of the radius of CNT), the THz absorption coefficient decreases monotonically. By analyzing the diffusion coefficient and dielectric relaxation dynamics, the hydrogen bond life, and the vibration density of the state of the water molecules in free solution and in CNTs, we conclude that the confinement effects on the THz spectra of biomolecule solutions are mainly to slow down the dynamics of water molecules and hence to reduce the THz absorption of the whole solution in confined environments.

Abstract-Separation of valley excitons in a MoS2 monolayer using a subwavelength asymmetric groove array

Liuyang Sun, Chun-Yuan Wang, Alex Krasnok, Junho Choi, Jinwei Shi, Juan Sebastian Gomez-Diaz, André Zepeda, Shangjr Gwo, Chih-Kang Shih, Andrea Alù, Xiaoqin Li

https://www.nature.com/articles/s41566-019-0348-z

Excitons in monolayer transition metal dichalcogenides are formed at K and K′ points at the boundary of the Brillouin zone. They acquire a valley degree of freedom, which has been explored as an alternative information carrier, analogous to charge or spin. Two opposite valleys in transition metal dichalcogenides can be optically addressed using light with different helicity. Here, we demonstrate that valley-polarized excitons can be sorted and spatially separated at room temperature by coupling a MoS2 monolayer to a subwavelength asymmetric groove array. In addition to separation of valley excitons in real space, emission from valley excitons is also separated in photon momentum-space; that is, the helicity of photons determines a preferential emission direction. Our work demonstrates that metasurfaces can facilitate valley transport and establish an interface between valleytronic and photonic devices, thus addressing outstanding challenges in the field of valleytronics.

Abstract-Electrically Reconfigurable Micromirror Array for Direct Spatial Light Modulation of Terahertz Waves over a Bandwidth Wider Than 1 THz

Jan Kappa, Dominik Sokoluk, Steffen Klingel, Corey Shemelya, Egbert Oesterschulze, Marco Rahm,

https://www.nature.com/articles/s41598-019-39152-y

We report the design, fabrication and experimental investigation of a spectrally wide-band terahertz spatial light modulator (THz-SLM) based on an array of 768 actuatable mirrors with each having a length of 220 μm and a width of 100 μm. A mirror length of several hundred micrometers is required to reduce diffraction from individual mirrors at terahertz frequencies and to increase the pixel-to-pixel modulation contrast of the THz-SLM. By means of spatially selective actuation, we used the mirror array as reconfigurable grating to spatially modulate terahertz waves in a frequency range from 0.97 THz to 2.28 THz. Over the entire frequency band, the modulation contrast was higher than 50% with a peak modulation contrast of 87% at 1.38 THz. For spatial light modulation, almost arbitrary spatial pixel sizes can be realized by grouping of mirrors that are collectively switched as a pixel. For fabrication of the actuatable mirrors, we exploited the intrinsic residual stress in chrome-copper-chrome multi-layers that forces the mirrors into an upstanding position at an inclination angle of 35°. By applying a bias voltage of 37 V, the mirrors were pulled down to the substrate. By hysteretic switching, we were able to spatially modulate terahertz radiation at arbitrary pixel modulation patterns.

Abstract-Evaluation of cancer tissue morphology via THz spectroscopic imaging: Human lung and small intestine malignancies

Woon-Gi Yeo, Ogan Gurel, Charles L. Hitchcock, Sungchan Park, Kubilay Sertel,  Niru K.Nahar,

https://www.sciencedirect.com/science/article/pii/S1350449518307862

We investigate the potential of terahertz spectroscopic imaging for assessment of malignant tissues in human lung and small intestine using a reflection-mode time-domain spectroscopy system spanning the 60 GHz–2 THz band. These two tissue groups are among the few that can be reached via an endoscopic sensor, thus potentially allowing for in-situ assessment of suspected tumors. As an initial study toward this goal, we characterized formalin-fixed and paraffin-embedded tissue blocks using a commercially-available reflection-mode time domain spectroscopy system. We verify that the measured THz responses of these tissue groups reveal key differences in their morphology, material density, and electrical properties. The spectroscopic characteristics in the THz band are contrasted with the histopathologic assessment of hematoxylin and eosin stained tissue slices to demonstrate the potential of THz spectroscopy for evaluating lung and small intestine malignancies. For both types of organ tissues, it is demonstrated that the THz images provide key discriminatory information such as tissue morphology, cancer margin, and necrotic areas in the tumor.

Abstract-Enhancement of Negative Differential Mobility Effect in Recessed Barrier Layer AlGaN/GaN HEMT for Terahertz Applications

Hongliang Zhao. Lin-An Yang, Hao Zou, Xiao-hua Ma, Yue Hao

https://ieeexplore.ieee.org/document/8634873

A recessed barrier layer (RBL) structure is proposed in the micrometer-sized AlGaN/GaN high-electron mobility transistor (HEMT) for terahertz applications. It is found by using numerical simulation that the properly designed RBL structure can trigger the formation and propagation of electron domains in the 2-D electron gas (2-DEG) channel. As a result, the fundamental frequency can be extended even up to terahertz regime, and also it can be tuned in a certain range by the bias voltage of Schottky contact gate that acts as a hot-electron injector just like the notch-doped Gunn diode. Our simulations show that the 0.3-μm -gate HEMT with the RBL structure having the depth of 10–15 nm and the length of 200–400 nm can generate the stable and tunable oscillations in the range of around 0.8–1.6 THz under the normally gate bias of −0.2–0.4 V, as well as the ratio of RF-to-dc current component ranging from 3.04% to 7.2%. These available characteristics come from the redistribution of electric field in the 2-DEG channel. Compared with the ungated and the top-gated planar Gunn diodes ever reported, the proposed RBL structural AlGaN/GaN HEMT can be easily fabricated and operated under normal conditions, demonstrating a great potential application in terahertz radiation sources.

Abstract-Inter-satellite Quantum Key Distribution at Terahertz Frequencies

Ziqing Wang, Robert Malaney, Jonathan Green

https://arxiv.org/abs/1902.07921

Terahertz (THz) communication is a topic of much research in the context of high-capacity next-generation wireless networks. Quantum communication is also a topic of intensive research, most recently in the context of space-based deployments. In this work we explore the use of THz frequencies as a means to achieve quantum communication within a constellation of micro-satellites in Low-Earth-Orbit (LEO). Quantum communication between the micro-satellite constellation and high-altitude terrestrial stations is also investigated. Our work demonstrates that THz quantum entanglement distribution and THz quantum key distribution are viable deployment options in the micro-satellite context. We discuss how such deployment opens up the possibility for simpler integration of global quantum and wireless networks. The possibility of using THz frequencies for quantum-radar applications in the context of LEO deployments is briefly discussed.

Terahertz wireless makes big strides in paving the way to technological singularity

Medical AI and doctors at earth stations could remotely conduct a zero-gravity operation aboard a space plane connected via terahertz wireless links.(CREDIT ©HIROSHIMA UNIVERSITY, NICT, PANASONIC, AND 123RF.COM)

https://www.eurekalert.org/pub_releases/2019-02/hu-twm021419.php

Hiroshima, Japan, February 19, 2019--Hiroshima University, National Institute of Information and Communications Technology, and Panasonic Corporation announced the successful development of a terahertz (THz) transceiver that can transmit or receive digital data at 80 gigabits per second (Gbit/s). The transceiver was implemented using silicon CMOS integrated circuit technology, which would have a great advantage for volume production. Details of the technology will be presented at the International Solid-State Circuits Conference (ISSCC) 2019 to be held from February 17 to February 21 in San Francisco, California [1].

The THz band is a new and vast frequency resource expected to be used for future ultrahigh-speed wireless communications. IEEE Standard 802.15.3d, published in October 2017, defines the use of the lower THz frequency range between 252 gigahertz (GHz) and 325 GHz (the "300-GHz band") as high-speed wireless communication channels. The research group has developed a single-chip transceiver that achieves a communication speed of 80 Gbit/s using the channel 66 defined by the Standard. The research group developed a 300-GHz-band transmitter chip capable of 105 Gbit/s [2] and a receiver chip capable of 32 Gbit/s [3] in the past few years. The group has now integrated a transmitter and a receiver into a single transceiver chip. 

"We presented a CMOS transmitter that could do 105 Gbit/s in 2017, but the performance of receivers we developed, or anybody else did for that matter, were way behind [3] for a reason. We can use a technique called 'power combining' in transmitters for performance boosting, but the same technique cannot be applied to receivers. An ultrafast transmitter is useless unless an equally fast receiver is available. We have finally managed to bring the CMOS receiver performance close to 100 Gbit/s," said Prof. Minoru Fujishima, Graduate School of Advanced Sciences of Matter, Hiroshima University.

"People talk a lot about technological singularity these days. The main point of interest seems to be whether artificial superintelligence will appear. But a more meaningful question to ask myself as an engineer is how we can keep the ever-accelerating technological advancement going. That's a prerequisite. Advances in not only computational power but also in communication speed and capacity within and between computers are vitally important. You wouldn't want to have a zero-grav operation on board a space plane without real-time connection with earth stations staffed by medical super-AI and doctors. After all, singularity is a self-fulfilling prophecy. It's not something some genius out there will make happen all of a sudden. It will be a distant outcome of what we develop today and tomorrow," said Prof. Fujishima.

"Of course, there still is a long way to go, but I hope we are steadily paving the way to such a day. And don't you worry you might use up your ten-gigabyte monthly quota within hours, because your monthly quota then will be in terabytes," he added.

Abstract-Investigation of liquid lines as terahertz emitters under ultrashort optical excitation

Qi Jin, Yiwen E, Shenghan Gao, Xi-Cheng Zhang

https://arxiv.org/abs/1902.07150

Recently, there has been growing interest in terahertz (THz) wave generation from liquids under optical excitation. Here, we propose and demonstrate the use of liquid lines in place of liquid films as THz emitters to boost THz signals. The geometry of the emitter eliminates the total internal reflection at the flat liquid-air interface. In addition, we observe that the polarity of the liquid has a significant influence on the THz wave generation. Alpha-pinene, a nonpolar liquid, offers much stronger THz radiation than water does. Besides paving the way to develop intense liquid THz sources, our work indicates that THz waves could be a tool for the further study of laser-liquid interaction.

Abstract-Multimillijoule coherent terahertz bursts from picosecond laser-irradiated metal foils

Guoqian Liao, Yutong Li, Hao Liu, Graeme G. Scott, David Neely, Yihang Zhang, Baojun Zhu, Zhe Zhang, Chris Armstrong, Egle Zemaityte, Philip Bradford, Peter G. Huggard, Dean R. Rusby, Paul McKenna, Ceri M. Brenner, Nigel C. Woolsey, Weimin Wang, Zhengming Sheng, and Jie Zhang

https://www.pnas.org/content/early/2019/02/12/1815256116


Ultrahigh-power terahertz (THz) radiation sources are essential for many applications, for example, THz-wave-based compact accelerators and THz control over matter. However, to date none of the THz sources reported, whether based upon large-scale accelerators or high-power lasers, have produced THz pulses with energies above the millijoule (mJ) level. Here, we report a substantial increase in THz pulse energy, as high as tens of mJ, generated by a high-intensity, picosecond laser pulse irradiating a metal foil. A further up-scaling of THz energy by a factor of ∼4 is observed when introducing preplasmas at the target-rear side. Experimental measurements and theoretical models identify the dominant THz generation mechanism to be coherent transition radiation, induced by the laser-accelerated energetic electron bunch escaping the target. Observation of THz-field-induced carrier multiplication in high-resistivity silicon is presented as a proof-of-concept application demonstration. Such an extremely high THz energy not only triggers various nonlinear dynamics in matter, but also opens up the research era of relativistic THz optics.

Abstract-Twisted Nematic Liquid-Crystal-Based Terahertz Phase Shifter using Pristine PEDOT: PSSTransparent Conducting Electrodes

Anup Kumar Sahoo, Chan-Shan Yang,  Chun-Ling Yen, Hung-Chun Lin, Yu-Jen Wang,  Yi-Hsin Lin, Osamu Wada ,Ci-Ling Pan,

https://www.mdpi.com/2076-3417/9/4/761

For this study, we demonstrated three different types of twisted nematic (TN) liquid crystal (LC) terahertz (THz) phase shifters using pristine poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) thin films as transparent conducting electrodes (TCEs). The transmittance of spin-coated pristine PEDOT: PSS thin film was as high as 92% in the frequency range of 0.2–1.2 THz. This is among the highest reported. Several TN-LC cells were constructed in a comparative study, which confirmed the reliability of pristine PEDOT: PSS as a TCE layer for THz phase shifter applications. The highest phase shift, required root-mean-square (RMS) driving voltage, and threshold voltage achieved by devices tested were 95.2° at 1 THz, 7.2 V_RMS, and 0.5 V_RMS, respectively. The thickness of the LC layer for the phase shifter was 250 µm, approximately half as thick as previous designs. In addition, the pristine PEDOT: PSS-based TN-LC phase shifter exhibited a figure-of-merit (FOM) value of approximately 6.65 degree·dB⁻¹·V⁻¹. This compared favorably with previously reported homogeneously aligned phase shifters with an FOM of 2.19 degree·dB⁻¹·V⁻¹. Our results indicated that a twisted nematic LC cell with pristine PEDOT: PSS thin films as electrodes is a good combination for a THz phase shifter and wave plates as well as other LC-based THz devices. 

Abstract-Hybrid Graphene-Plasmonic Gratings to Achieve Enhanced Nonlinear Effects at Terahertz Frequencies

Tianjing Guo, Boyuan Jin, and Christos Argyropoulos

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.11.024050

High input intensities are usually required to efficiently produce nonlinear optical effects in ultrathin structures due to their extremely weak nature. This problem is particularly critical at low terahertz frequencies because high-input-power terahertz sources are not available. The demonstration of enhanced nonlinear effects at terahertz frequencies is particularly important since these nonlinear mechanisms promise to play a significant role in the development and design of new reconfigurable planar terahertz nonlinear devices. In this work, we present an alternative class of ultrathin nonlinear hybrid planar terahertz devices based on graphene-covered plasmonic gratings exhibiting very large nonlinear response. The robust localization and enhancement of the electric field along the graphene monolayer, combined with the large nonlinear conductivity of graphene, can lead to boosted third-harmonic-generation and four-wave-mixing nonlinear processes at terahertz frequencies. These interesting nonlinear effects exhibit very high nonlinear conversion efficiencies and are triggered by realistic input intensities with relatively low values. In addition, the third-harmonic-generation and four-wave-mixing processes can be significantly tuned by the dimensions of the proposed hybrid structures, the doping level of graphene, or the input intensity, whereas the nonlinear radiated power remains relatively insensitive to the incident angle of the excitation source. The nonlinear hybrid graphene-covered plasmonic gratings presented have a relative simple geometry and, as a result, can be used to realize efficient third-order nonlinear terahertz effects with a limited fabrication complexity. Several new nonlinear terahertz devices are envisioned on the basis of the proposed hybrid nonlinear structures, such as frequency generators, all-optical signal processors, and wave mixers. These devices are expected to be useful for nonlinear terahertz spectroscopy, noninvasive terahertz subwavelength imaging, and terahertz communication applications.

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Abstract- Terahertz Atmospheric Windows for High Angular Resolution Terahertz Astronomy from Dome A

Hiroshi Matsuo, Sheng-Cai Shi, Scott Paine, Qi-Jun Yao, Zhen-Hui Lin

https://arxiv.org/abs/1902.06398

Atmospheric transmission from Dome A, Antarctica, presents new possibilities in the field of terahertz astronomy, where space telescopes have been the only observational tools until now. Using atmospheric transmission measurements from Dome A with a Fourier transform spectrometer, transmission spectra and long-term stabilities have been analyzed at 1.461 THz, 3.393 THz, 5.786 THz and 7.1 THz, which show that important atmospheric windows for terahertz astronomy open for a reasonable length of time in the winter season. With large aperture terahertz telescopes and interferometers at Dome A, high angular resolution terahertz observations are foreseen of atomic fine-structure lines from ionized gas and a water ice feature from protoplanetary disks.

Abstract-Tunable hybridization of graphene plasmons and dielectric modes for highly confined light transmit at terahertz wavelength

X. Q. He, T. G. Ning, L. Pei, J. J. Zheng, J. Li, and X. D. Wen

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-5-5961

We theoretically report a novel graphene-based hybrid plasmonic waveguide (GHPW) by integrating a GaAs micro-tube on a silica spacer that is supported by a graphene-coated substrate. In comprehensive numerical simulations on guiding properties of the GHPW, it was found that the size of hybrid plasmonic mode (TM) can be reduced significantly to ~10−4(λ2/4), in conjunction with long propagation distances up to tens of micrometers by tuning the the waveguide’s key structure parameters and graphene’s chemical potential. Moreover, crosstalk between two adjacent GHPWs that are placed on the same substrate has been analyzed and ultralow crosstalk can be realized. The proposed scheme potentially enables realization of the various high performance nanophotonic components-based subwavelength plasmonic waveguides in terahertz domain.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-5-5961

Radar to spot the bad guys from on high

http://www.china.org.cn/china/2019-02/15/content_74467346.htm

China's space engineers said they can now offer a new method to detect terrorists transporting explosives as well as track moving targets more efficiently than current modalities.

Researchers at the Beijing Institute of Radio Measurement, affiliated with the China Aerospace Science and Industry Corp, said they have developed the country's first terahertz radiation-enabled synthetic-aperture radar and they are working to utilize the technology in public security work.

Li Jun, a senior designer at the institute, explained that a terahertz is a unit of the electromagnetic spectrum between the microwave and the optical wavelengths. Among terahertz radiation's many physical characteristics, it has a special ability to identify proteins, the building blocks of living organisms. It can also detect TNT, one of the most oft used explosive materials, and can therefore be used to detect individuals carrying the material on their persons.

"Currently, it is very difficult for public security authorities to screen people for firearms or explosive devices from long, safe distances. Most methods rely on handheld detectors and visual clues, forcing law-enforcement personnel to check suspected people within a short range or manually and this has proved to be time-consuming and dangerous," Li said.

By comparison, terahertz radiation-enabled radar takes advantage of its high penetration capability, and is able to detect explosives and reveal hidden weapons from afar, which helps to improve safety at public buildings and at large events, as well as the safety of security officers, he said.

In addition to its potential applications in remote detection work, the radar technology also offers better solutions for law enforcement departments' surveillance of criminal suspects or terrorists, Li said.

"Existing optical, infrared or radar systems are subject to a host of external factors such as sunlight, cloud or smog, when they are used to monitor and track people on the move. But terahertz technology is immune to these factors, reducing the risk of losing targets," he said.

The institute is a leading research body in radar and terahertz technology in China and has taken part in the development of many advanced defense technologies. Encouraged by the government's policies to foster transfer of defense technologies to civilian industries, institute designers have been seeking to make use of their expertise to assist other sectors, Li said.

Engineers have built prototypes of terahertz radiation-enabled synthetic-aperture radar and are conducting tests.

"We mounted a prototype on a drone and recently conducted test flights in Shaanxi province," Li said. "A typical application of the radar in the future can be drone-based to help with large-scale detection of explosive-carrying terrorists or the placement of improvised explosive devices. This will be much more efficient and safer than deploying a lot of security personnel to do the same work."

Drones equipped with the radar can also perform uninterrupted surveillance of suspects, he added.

Abstract-Controllable nonlinear optics in the GHz-THz range

Apostolos Apostolakis, Mauro F. Pereira

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10926/109262G/Controllable-nonlinear-optics-in-the-GHz-THz-range/10.1117/12.2516886.short?SSO=1

This paper implements a simple optical method to forecast power output of superlattice multipliers which are subjected to an external GHz-THz field. These results complement a recent study which addressed the harmonic conversion efficiency in semiconductor superlattices by interface roughness design. Applying a strong ac field on such a device pumps energy into the system, which is then converted to radiation at harmonics of the pump frequency. Here we investigate the odd harmonics generation in an unbiased superlattice at room temperature, after excitation by input signals in a wide frequency range which can provided by realistic devices.

© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Terahertz toroidal metamaterial with tunable properties

Zhengyong Song, Yide Deng, Yuanguo Zhou, and Zhaoyuan Liu

Fig. 2 (a) Simulated transmission spectra of the proposed toroidal dipole. Simulated electric current (b) and magnetic field (c) distributions at the resonant frequency of 0.288 THz, when the conductivity of 𝑉𝑂2$V{O}_2$ is10 𝛺−1𝑐𝑚−1$10{\Omega }^{-1}c{m}^{-1}$.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-4-5792

We present a tunable metamodulator to work at terahertz frequencies by employing the dependency of toroidal dipolar resonance on the conductivity of vanadium dioxide. Numerical results show that toroidal dipolar resonance in the proposed planar structure can be observed around 0.288 THz in transmission spectrum. From the distribution of the anti-phase current flowing in the symmetric split ring resonator, the formation of toroidal dipole is validated. Our design may have potential applications in advanced terahertz devices, such as filter, plasmonic sensor, and fast switch.

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