Abstract-Full 3D+1 modelling of the tilted-pulse-front setups for single-cycle terahertz generation

Lu Wang, Tobias Kroh, Nicholas H. Matlis, Franz Kaertner

https://arxiv.org/abs/1908.09581

The tilted-pulse-front setup utilizing a diffraction grating is one of the most successful methods to generate single- to few-cycle terahertz pulses. However, the generated terahertz pulses have a large spatial inhomogeneity, due to the noncollinear phase matching condition and the asymmetry of the prism-shaped nonlinear crystal geometry, especially when pushing for high optical-to-terahertz conversion efficiency. A 3D+1 (x,y,z,t) numerical model is necessary in order to fully investigate the terahertz generation problem in the tilted-pulse-front scheme. We compare in detail the differences between 1D+1, 2D+1 and 3D+1 models. The simulations show that the size of the optical beam in the pulse-front-tilt plane sensitively affects the spatio-temporal properties of the terahertz electric field. The terahertz electric field is found to have a strong spatial dependence such that a few-cycle pulse is only generated near the apex of the prism. The part of the beam farther from the apex contains a large fraction of the energy but has a waveform that deviates from a few-cycle. This strong spatial dependence must be accounted for when using the terahertz pulses for strong-field physics and carrier-envelope-phase sensitive experiments such as terahertz acceleration, coherent control of antiferromagnetic spin waves and terahertz high-harmonic generation.

LUNA Blog-TeraMetrix to Attend IRMMW in Paris

https://lunainc.com/terametrix-attend-irmmw-paris/?fbclid=IwAR1x1877hWlaNKPtvz147QlZ1M-fm9ylAvEvPgl6pPvpjIZCeM-tyvdx9IA

TeraMetrix will be attending the 44^th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW – THz 2019) in Paris, France, September 1-6. TeraMetrix will have a booth in the exhibition are on the first floor of the conference venue to demonstrate and discuss our products and the advantages of terahertz technology.

In addition to having a booth in the exhibition hall TeraMetrix’s Irl Duling will be giving a presentation on Wednesday, September 4, at 3:45pm on how terahertz technology can be used in industrial environments. The presentation will focus on how TeraMetrix’s technology is used in the online measurement of tire ply balance to improve manufacturing quality and reduce material cost, saving up to $500,000 per year.

Where to find TeraMetrix at IRMMW:

Booth: N° 28 (Exhibition Hall, 1^st floor, in the gallery section)

Presentation: Wednesday, September 4, 3:45pm.

For additional information on using terahertz technology to measure total thickness of manufacturing materials be sure to check out the TeraMetrix blog.

Abstract-Novel terahertz sources in the form of multi-spectral resonators boosted by both pump light local field enhancement and terahertz Purcell effect

Zhanghua Han, Yangjian Cai, Uriel Levy, Sergey I Bozhevolnyi

https://pubs.acs.org/doi/abs/10.1021/acsphotonics.9b00322

Most terahertz sources nowadays are still inefficient and have low output powers, especially for the continuous-wave THz radiations in the 1~2 THz band, impeding the further development of terahertz science and its applications in various fields. While considerable research effort has been made on the improvement of conversion efficiency from optical/electrical energy to terahertz radiations, less effort is made to maximize the extraction of terahertz energy from the chip to the far field. In this paper, we show a scheme that these two goals can be met simultaneously by making use of multi-spectral resonators, which resonate both in the terahertz band to improve terahertz extraction via Purcell effect and in the optical frequencies exhibiting huge local field enhancement to improve the optical-to-terahertz conversion. Using the nonlinear process of difference frequency generation as an example, our results show that combing a large split-ring resonator (SRR) as a terahertz resonator and nanoscale bowtie optical antennas embedded in the SRR slit, an overall enhancement factor larger than 2×105 in the radiated terahertz power to the free space can be achieved compared to the case when the metallic structures are absent. This scheme of multi-spectral resonators can be extended to other terahertz sources, like the photoconductive antennas, and help realize more efficient terahertz sources.

Terahertz screening tech reduces airport throughput time

https://www.electronicsweekly.com/news/business/terahertz-screening-tech-reduces-airport-throughput-time-2019-08/

By David Manners

Sales of equipment used to screen people for explosives, weapons and contraband will grow at 6.6%  between 2018 and 2023, says IHS Markit.

Emerging technologies, including millimeter and terahertz waves, are being used for passenger screening at airports.

These technologies now promise to increase security in other applications and better protect visitors at large event venues and in open areas.

Public transport and event security face many challenges, with suicide bombings, public-area shootings and knife attacks now more likely than ever.

Traditional event security has focused on manual searches of bags or the use of bag X-ray scanners and metal detectors.

X-ray bag scanning and metal detection are time-consuming processes.

In the case of public transportation hubs, security is provided by CCTV and monitoring to spot threats.

However, operators will not be able to spot all unusual behaviors, and they will not be able to assess whether a suspicious situation involves explosives.

Open areas are even more difficult to protect, prompting work on equipment as part of a concept of stand-off detection, where scanning for explosives or contraband can be performed at a distance from the potential source.

Terahertz technology, specifically, offers a solution to these challenges by allowing the scanning of a large number of people without requiring them to stop for a security check. This is particularly vital for high-throughput areas such as train stations or open areas.

Even though the detection process is more challenging due to high speed of people’s movement, machine learning and analytics can help improve the accuracy of the detection process.

This will help reduce false alarms, which can be a particular challenge in such complex environments.

Terahertz devices are also small enough to be located in inconspicuous, strategic spots around the area, which can help extend the security perimeter away from the most sensitive parts and avoid impeding the flow of people.

Another benefit of terahertz devices is that they do not emit radiation, and instead only read gaps in natural radiation emitted by human body.

This is an important factor in addressing concerns over long-term safety of exposure to various types of radiation.

Deployment of people-screening devices in non-traditional applications such as event venues and public transportation stations is likely to elicit controversy and may inadvertently create a feeling of panic.

Even though the industry has successfully managed to commercialize terahertz technology, its practical application may require much more testing before wider deployment is possible.

Also, in case of a positive detection, the details of operational response by police or security services would have to be carefully elaborated to prevent panic and disruption.

False positives and negatives can be particularly problematic in public transportation settings as people usually rush for trains to get to workplaces and appointments.

Any further disruptions to their journeys would have a negative impact on the railroads’ business and customer satisfaction, with the disruption being blamed on the train companies.

Also, terahertz devices cannot be treated as a panacea for the expected threats. Furthermore, if there is a false negative detection that results in an incident, the backlash against the technology may be significant.

Keysight extends beyond 5G with participation in 6G flagship program

The next generation of wireless communications is expected to leverage spectrum above millimeter waves.

https://www.fiercewireless.com/wireless/keysight-extends-beyond-5g-participation-6g-flagship-program

by Monica Alleven

While the wireless industry is firmly entrenched in deploying 5G networks—and in many cases, busy debunking myths surrounding it—plenty of academics and others are exploring what’s going to happen after 5G.

Test and measurement company Keysight Technologies, which has been there throughout the 5G standards process and even before that, recently announced that it has joined the multi-party 6G Flagship Program supported by the Academy of Finland and led by the University of Oulu, Finland.

Keysight actually has had a long relationship with Oulu University and has an R&D team based in Oulu, according to Roger Nichols, 5G program manager at Keysight, so it’s not as if this is coming out of the blue. According to a press release, however, Keysight is the only test and measurement provider thus far invited to take part in the program.

Keysight said its early research capability, complemented by a range of software and hardware for design, simulation and validation, will help the program accomplish its overarching goals. Those goals include supporting the industry in finalizing the adoption of 5G across verticals, developing fundamental technologies needed to enable 6G such as artificial intelligence (AI) and intelligent UX, and speeding digitalization of society.

The next generation of wireless communications is expected to leverage spectrum above millimeter waves. The terahertz waves, from 300 GHz to 3 THz, form an important component in delivering data rates of up to one terabit per second and ultra-low latencies, but they are still very much in the experimental territory.

“A lot of what’s happening up there now is still in the research phase because as you can imagine in those higher frequencies, it’s challenging to get things to work the way you want them,” Nichols told FierceWirelessTech. “We’ve been involved in that territory for quite a while,” having sub-100 GHz capability in its equipment for decades and using third-parties to extend that up into the terahertz range.

It’s not just about higher frequencies but what can be done with the wide bandwidths. For the sake of 6G, “really this is about: can we get an even wider bandwidth to deal with new applications that we haven’t thought about that have a demand for data rates that are well beyond anything we’re considering for 5G?” he said. “Obviously, going to terahertz super wide bandwidth is only part of 6G, just like millimeter wave is only part of 5G.”

Nichols points to an ITU Network 2030 white paper that describes the Network 2030 initiative and provides a comprehensive analysis of the applications, network, and infrastructure envisioned for the next big wireless transformation. That paper points to holographic type communications, multi-sense networks, time-engineered applications and critical infrastructure as emerging applications or use cases.

But nobody is suggesting it's a good idea to get ahead of themselves. Part of Keysight’s success in 5G was getting involved early and knowing where that technology was headed and the tools that are needed, plus developing relationships with academia and industry. “Clearly, we’re going to spend our time ensuring that we stay on top of that business opportunity, which is far from being over,” he said.

Abstract-Terahertz radiation of microcavity dipolaritons

A. Seedhouse, J. Wilkes, V. D. Kulakovskii, and E. A. Muljarov

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-17-4339

We propose the use of dipolaritons—quantum well excitons with a large dipole moment, coupled to a planar microcavity—for generating terahertz (THz) radiation. This is achieved by exciting the system with two THz detuned lasers that leads to dipole moment oscillations of the exciton polariton at the detuning frequency, thus generating a THz emission. We have optimized the structural parameters of a system with microcavity embedded AlGaAs double quantum wells and shown that the THz emission intensity is maximized if both of the laser frequencies match different dipolariton states. The influence of the electronic tunnel coupling between the wells on the frequency and intensity of the THz radiation is also investigated, demonstrating a trade-off between the polariton dipole moment and the Rabi splitting.

© 2019 Optical Society of America

Abstract-Resonant-tunneling-diode terahertz oscillator with a cylindrical cavity for high-frequency oscillation

AIP Advances

Ryunosuke Izumi, Takumi Sato, Safumi Suzuki, Masahiro Asada

Schematic structure of the proposed oscillator.

https://aip.scitation.org/doi/abs/10.1063/1.5114963

We proposed and fabricated resonant-tunneling-diode (RTD) terahertz oscillators integrated with a cylindrical cavity. Oscillation frequency of 3 THz is expected from theoretical analysis. As a preliminary experiment, the proposed oscillator was fabricated using electron-beam lithography with a three-layer-resist process. An oscillation of up to 1.79 THz was obtained in the fabricated oscillators, which was lower than the theoretical expectation. This was because of a parasitic capacitance of the metal post connecting the cavity and the RTD. Theoretical calculations, including this parasitic capacitance, agreed well with the experiment. The parasitic capacitance can be suppressed by adding a simple process to the cavity fabrication. 

A laser for penetrating waves

https://www.intelligent-aerospace.com/resources/article/14038472/a-laser-for-penetrating-waves-terahertz-data-transmission

DRESDEN, Germany - The Landau-level laser is an exciting concept for an unusual radiation source. It could efficiently generate so-called terahertz waves, which can be used to penetrate materials, with possible applications in data transmission. So far, however, nearly all attempts to make such a laser have failed. An international team of researchers has now taken an important step in the right direction: In the journal Nature Photonics, they describe a material that generates terahertz waves by simply applying an electric current. Physicists from the German research center Helmholtz-Zentrum Dresden-Rossendorf (HZDR) played a significant role in this project, says Phys.org. Continue reading original article

The Intelligent Aerospace take:

August 19,2019- The Helmholtz Association of German Research Centres describe a material that generates terahertz waves by applying an electric current. Currently, teraherz waves are used in detecting objects under clothing in airports, but the high-frequency waves could drive innovation in data transmission. Fiber optic cables use light to transfer data at much faster rates compared to traditional copper connectors, but a tunable laser capable of transmitting the high frequency has not yet been developed. However, with terahertz waves transmitting at frequencies at 1000 times higher than current WLAN technologies, the technology could prove useful in moving large amounts of data across short distances should some very difficult tech hurdles be cleared.

Abstract-Terahertz Wave Modulation by Pre-plasma Using Different Laser Wavelength

Tong Wu, Liquan Dong, Rui Zhang, Hang Zhao, Yuejin Zhao, Cunlin Zhang, Liangliang Zhang

https://link.springer.com/article/10.1007%2Fs10762-019-00618-9

We report the terahertz (THz) wave modulation from a pre-plasma using different laser wavelengths, which is intersected orthogonally to the two-color laser filament produced by 800-nm laser pulse. When the pre-plasma exists, the THz radiation excited by the two-color field decreases significantly and the modulation depth increases with the increasing modulation pulse wavelength. Moreover, the amplitude reduction at high frequency in THz spectrum and the THz wave polarization change also have the modulation pulse wavelength dependence. These results can be explained by a photocurrent model considering wavelength-dependent ionization rate. The work contributes to further understand the theoretical mechanism of THz wave generation and enrich the practical application of ultrafast THz modulator.

Abstract-Far-infrared terahertz properties of L-cysteine and its hydrochloride monohydrate

Guanhua Ren, Siqi Zong, Zhongjie Zhu, Chao Cheng. Ligang Chen,  Lu. Zhou, Jianbing Zhang, Liyuan Liu, Jiaguang Han, Hongwei Zhao

https://www.sciencedirect.com/science/article/pii/S1386142519308662

As the building blocks of proteins, amino acids serve vital metabolic functions in addition to protein synthesis and thus attract enormous interest. Here we reported the far-infrared optical properties of L-cysteine (Lcys) and its hydrochloride monohydrate (LCHM) characterized by terahertz time-domain spectroscopy. The Lcys and LCHM exhibit quite distinct characteristics in the terahertz region due to diverse collective vibrations of the molecules, which is further confirmed by the solid-state density functional theory (DFT) calculations. The presented studies indicate that the intermolecular hydrogen bonds play a critical role in the far-infrared terahertz response of Lcys and LCHM.

Abstract-Terahertz spin dynamics driven by a field-derivative torque

Ritwik Mondal, Andreas Donges, Ulrike Ritzmann, Peter M. Oppeneer, and Ulrich Nowak

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.100.060409

Efficient manipulation of magnetization at ultrashort timescales is of particular interest for future technology. Here, we numerically investigate the influence of the so-called field-derivative torque, which was derived earlier based on relativistic Dirac theory [R. Mondal et al., Phys. Rev. B 94, 144419 (2016)], on the spin dynamics triggered by ultrashort laser pulses. We find that only considering the THz Zeeman field can underestimate the spin excitation in antiferromagnetic oxide systems such as, e.g., NiO and CoO. However, accounting for both the THz Zeeman torque and the field-derivative torque, the amplitude of the spin excitation increases significantly. Studying the damping dependence of the field-derivative torque we observe larger effects for materials having larger damping constants.

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Abstract-Generation of arbitrarily chirped and CEP-controlled terahertz pulses for dispersion compensation using an optical pulse shaping technique and a fan-out periodically poled crystal

Hisanari Takahashi, Yoichi Kawada, Hiroshi Satozono, Koji Takahashi, Koyo Watanabe, Takashi Inoue, and Hironori Takahashi

Fig. 1. A concept for generating phase-controlled THz pulses. THz-BS: THz beam splitter; SLM: spatial light modulator.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-18-25305

We constructed a system that can generate phase-controlled terahertz (THz) pulses using a fan-out periodically poled lithium tantalate crystal and an optical pulse shaper containing a spatial light modulator. The phase of each THz frequency components could be controlled by manipulating the delay time of the corresponding optical pulses. Using the system, we generated arbitrarily group-velocity-dispersion-controlled THz pulses, where the chirp parameter was 2.53 ps2/rad between 0.6 and 1.5 THz. In addition, we generated arbitrarily carrier-envelope-phase-controlled THz pulses in the same system. Phase-controlled THz pulses may be useful for applications such as dispersion compensation.

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

Abstract-A Comprehensive Review on Food Applications of Terahertz Spectroscopy and Imaging

Leili Afsah‐Hejri,  Parvaneh Hajeb,   Parsa Ara, Reza J. Ehsani,

Location of THz region in the Electromagnetic Spectrum and some applications of THz spectroscopy and imaging.

https://onlinelibrary.wiley.com/doi/full/10.1111/1541-4337.12490

Food product safety is a public health concern. Most of the food safety analytical and detection methods are expensive, labor intensive, and time consuming. A safe, rapid, reliable, and nondestructive detection method is needed to assure consumers that food products are safe to consume. Terahertz (THz) radiation, which has properties of both microwave and infrared, can penetrate and interact with many commonly used materials. Owing to the technological developments in sources and detectors, THz spectroscopic imaging has transitioned from a laboratory‐scale technique into a versatile imaging tool with many practical applications. In recent years, THz imaging has been shown to have great potential as an emerging nondestructive tool for food inspection. THz spectroscopy provides qualitative and quantitative information about food samples. The main applications of THz in food industries include detection of moisture, foreign bodies, inspection, and quality control. Other applications of THz technology in the food industry include detection of harmful compounds, antibiotics, and microorganisms. THz spectroscopy is a great tool for characterization of carbohydrates, amino acids, fatty acids, and vitamins. Despite its potential applications, THz technology has some limitations, such as limited penetration, scattering effect, limited sensitivity, and low limit of detection. THz technology is still expensive, and there is no available THz database library for food compounds. The scanning speed needs to be improved in the future generations of THz systems. Although many technological aspects need to be improved, THz technology has already been established in the food industry as a powerful tool with great detection and quantification ability. This paper reviews various applications of THz spectroscopy and imaging in the food industry.

Abstract-Prospects of designing gold-nanoparticles-based soft terahertz radiation sources and terahertz-to-infrared converters for concealed object detection technology

K. A. Moldosanov, A. V. Postnikov, V. M. Lelevkin, N. J. Kairyev

https://arxiv.org/abs/1908.07991

The two-phonon scheme of generation of terahertz (THz) photons by gold nanobars (GNBs) is considered. It is shown that in GNBs, by choosing their sizes, it is possible to provide conditions for converting the energy of longitudinal phonons with THz frequencies into the energy of THz photons. The prospects of designing GNBs-based soft THz radiation sources (frequencies: 0.14; 0.24; 0.41 and 0.70 THz) with a large flow cross-section (diameter ~40 cm) intended for detection of hidden objects under clothing to ensure security in public places (airports, railway stations, stadiums, etc.) are assessed. The choice of the above frequencies is a compromise between the requirements of low absorption of THz radiation by water vapor in air, good penetration through the fabric of clothing, favoring a sufficient resolution of the imaging system, and an abundance of corresponding longitudinal phonons, capable of exciting Fermi electrons in GNBs. Estimates of the characteristics of the terahertz-to-infrared converter based on gold nanospheres (GNSs), which could work in tandem with these sources of THz radiation -- as a means of visualization of hidden objects -- are also given.

Book-Overview of Opto-Electrical Terahertz Spectroscopy

Blaž Pongrac,  Dušan Gleich

https://ieeexplore.ieee.org/document/8787275

Terahertz spectrometry offers new opportunities in material research, mostly because THz waves are non-destructive to biological and opaque materials. The technology is still not widely available, but there is a high demand for it. There are three main methods of generating THz waves. The most promising; however, still not a full- fledged method is the opto-electrical method, which is presented in this paper. A demonstration of sample measurements is also presented.

Tuning Quantum States of Matter Using Ultrafast Photonics

Jigang Wang and his research group use quantum terahertz spectroscopy to access, study, and control quantum states of matter. The research group, (l) to (r): Zhaoyu Liu, Liang Luo, Chirag Vaswani, Di Cheng, Jigang Wang, Dinusha Mudiyanselage, Richard H. Kim, and Chuankun Huang. Courtesy of Christopher Gannon/Iowa State University. 

https://www.photonics.com/Article.aspx?AID=65050


AMES, Iowa, Aug. 23, 2019 — Researchers at Iowa State University, led by professor Jigang Wang, are using quantum terahertz spectroscopy to explore and control quantum states of matter. The researchers have announced three discoveries based on their studies. 

The first, reported in Nature Materials, describes how ultrafast pulses of photons — pulsed at trillions of cycles per second — can switch on a state of matter hidden by the superconductive flow of electricity at ultracold temperatures. The researchers demonstrated a tuning knob for switching on exotic, hidden states without changing the temperature. Such a tuning knob, called a quantum quench, could further the research and discovery of nonequilibrium materials. 

The second finding, reported in Physical Review Letters, describes how the group’s terahertz instrumentation traced electron pairings in materials, revealing a new, light-induced, long-lived state of matter. 

The third discovery, reported in Nature Photonics, describes how ultrafast pulses of photons can be used like a tuning knob to control and accelerate supercurrents. The ultrafast light pulses break equilibrium symmetry, triggering quantum oscillations that, according to the researchers, cannot be achieved by any other means. 

Wang said that the team would like to use these ultrafast pulses and high frequencies of light to probe smaller scales, in the 1 to 10 nm range. “We’d also like to develop controls using terahertz light for the quantum computation community,” he said. 

Wang believes that the intense terahertz flashes produced by his laboratory instruments can be a control knob for finding, stabilizing, probing, and potentially controlling exotic states and their unique properties. “We have established a new approach to access and potentially control exotic states of matter,” he said. 

The research was published in Nature Materials (https://doi.org/10.1038/s41563-018-0096-3), Physical Review Letters (https://doi.org/10.1103/PhysRevLett.121.267001), and Nature Photonics (https://doi.org/10.1038/s41566-019-0470-y).

Abstract-Terahertz beam spot size measurements by a CCD camera

O. V. Chefonov, A. V. Ovchinnikov, M. B. Agranat, and A. N. Stepanov

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-17-4099

We present the experimental data on the direct measurements of spatial distribution of the terahertz (THz) pulse intensity profile using a commercial silicon-based charge-coupled device (CCD) camera in the spectral range from 1–3 THz. A method to measure the dimensions of a high-intensity THz radiation beam in the focal plane using the CCD camera is proposed and experimentally verified.

© 2019 Optical Society of America

Abstract-High-speed efficient terahertz modulation based on tunable collective-individual state conversion within an active 3nm-two dimensional electron gas metasurface

Yuncheng Zhao, Lan Wang, Yaxin Zhang, Shen Qiao, Shixiong Liang, Xilin Zhang, Xiaoqing Guo, Zhihong Feng, Feng Lan, Zhi Chen, Xiaobo Yang, Ziqiang Yang,

https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.9b01273#

Terahertz (THz) modulators are always realized by dynamically manipulating the conversion between different resonant modes within a single unit cell of an active metasurface. In this paper, to achieve real high-speed THz modulation, we present a staggered netlike two-dimensional electron gas (2DEG) nanostructure composite metasurface that has two states: a collective state with massive surface resonant characteristics and an individual state with meta-atom resonant characteristics. By controlling the electron transport of the nanoscale 2DEG with an electrical grid, collective-individual state conversion can be realized in this composite metasurface. Unlike traditional resonant mode conversion confined in meta-units, this state conversion enables the resonant modes to be flexibly distributed throughout the metasurface, leading to a frequency shift of nearly 99% in both the simulated and experimental transmission spectra. Moreover, such a mechanism can effectively suppress parasitic modes and significantly reduce the capacitance of the metasurface. Thereby, this composite metasurface can efficiently control the transmission characteristics of THz waves with high-speed modulations. As a result, 93% modulation depth is observed in the static experiment and modulated sinusoidal signals up to 3 GHz are achieved in the dynamic experiment while the -3dB bandwidth can reach up to 1GHz. This tunable collective-individual state conversion may have great application potential in wireless communication and coded imaging.

Abstract-Terahertz Time‐Domain Spectroscopy and Near‐Field Microscopy of Transparent Silver Nanowire Networks

Niels van Hoof  Matteo Parente  Andrea Baldi  Jaime Gómez Rivas

https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.201900790?af=R

Transparent conductive layers are key components of optoelectronic devices. Here, a polyol method is used to synthesize large quantities of monodisperse silver nanowires (AgNWs) and these are used to fabricate transparent conducting networks over large areas. The optical extinction and terahertz (THz) conductance of these networks are simultaneously investigated, using optical and THz spectroscopy, and THz near‐field microscopy. The combination of optical and THz measurements allows the identification of transparent regions with high conductance. The THz near‐field measurements reveal local variations in the THz transmission and conductance that are averaged in far‐field measurements. These results demonstrate that THz near‐field microscopy is a powerful tool for the quantitative investigation of new conductive transparent electrodes.

Abstract-Image denoising and enhancement of terahertz passive imaging

Yashang Li; Guozhong Zhao

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11179/111790X/Image-denoising-and-enhancement-of-terahertz-passive-imaging/10.1117/12.2539884.short

The wavelength of the terahertz is between the infrared and the microwave, and the photon energy is low, so it has great application prospects in security inspection. In order to further improve the target resolution of terahertz passive imaging system, A terahertz image enhancement method based on a block matching and three-dimensional and weighted Schatten-p norm minimization is proposed to improve the image resolution of terahertz passive imaging system. It uses three-dimensional matched filtering to remove image noise on the basis of mean filtering, and then adopts Lucy Richardson algorithm and weighted Schatten-p norm minimization for image restoration. Finally, the convolution filter is used to enhance image details and the background of the image is subtracted by the edge detection. The method of paper significantly enhances the image contrast and increases system resolution from 2cm to 1.5cm, effectively improving system performance

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

Abstract-Dynamically controllable graphene terahertz splitters with nonreciprocal properties

Victor Dmitriev and Wagner Castro

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-58-24-6513

Two novel graphene-based nonreciprocal four-port splitters for the terahertz region are proposed. The input power is divided between two output ports, whereas the input port is isolated from the output ports due to the presence of the fourth port. The splitters consist of a circular graphene resonator and four graphene waveguides coupled to the resonator. These elements are placed on the two-layer dielectric substrate. The central part of the splitter is under a biasing DC magnetic field normal to the graphene layer. The surface plasmon-polariton wave in the input port excites the dipole resonance in the resonator. The splitters have the following parameters: the input power is divided between two output ports almost equally with −4.4  dB$-4.4\mathrm{dB}$. The input port is isolated from two output ports by −15  dB$-15\mathrm{dB}$. The bandwidth is 4.0% with a central frequency of 7.4 THz. The biasing DC magnetic field is 0.8 T, and the Fermi energy of graphene 𝜖𝐹=0.15  eV${ϵ}_F=0.15\mathrm{eV}$. Changing the Fermi energy by electrostatic gating allows one to dynamically control the central frequency of the splitters.

© 2019 Optical Society of America