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Terahertz

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https://www.readbyqxmd.com/read/28634341/terahertz-circular-airy-vortex-beams
#1
Changming Liu, Jinsong Liu, Liting Niu, Xuli Wei, Kejia Wang, Zhengang Yang
Vortex beams have received considerable research interests both in optical and millimeter-wave domain since its potential to be utilized in the wireless communications and novel imaging systems. Many well-known optical beams have been demonstrated to carry orbital angular momentum (OAM), such as Laguerre-Gaussian beams and high-order Bessel beams. Recently, the radially symmetric Airy beams that exhibit an abruptly autofocusing feature are also demonstrated to be capable of carrying OAM in the optical domain...
June 20, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28621956/controlled-terahertz-birefringence-in-stretched-poly-lactic-acid-films-investigated-by-terahertz-time-domain-spectroscopy-and-wide-angle-x-ray-scattering
#2
Hotsumi Iwasaki, Madoka Nakamura, Nozomu Komatsubara, Makoto Okano, Masayoshi Nakasako, Harumi Sato, Shinichi Watanabe
We report a correlation between the dielectric property and structure of stretched poly(lactic acid) (PLA) films, revealed by polarization-sensitive terahertz time-domain spectroscopy and two-dimensional (2D) wide-angle X-ray scattering (WAXS). The experiments evidence that the dielectric function of the PLA film becomes more anisotropic with increasing draw ratio (DR). This behavior is explained by a classical Lorentz oscillator model assuming polarization-dependent absorption. The birefringence can be systematically altered from 0 to 0...
June 16, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28615684/flat-terahertz-reflective-focusing-metasurface-with-scanning-ability
#3
Huan Yi, Shi-Wei Qu, Bao-Jie Chen, Xue Bai, Kung Bo Ng, Chi Hou Chan
The ability to manipulate the propagation properties of electromagnetic waves, e.g., divergence, focusing, holography or deflection, is very significant in terahertz applications. Metasurfaces with flat structures are attractive for achieving such manipulations in terahertz band, as they feature low profile, lightweight, and ease of design and installation. Several types of terahertz reflective or transmitting metasurfaces with focusing function have been implemented recently, but none of them can provide scanning ability with controllable focus...
June 14, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28615654/6-2-ghz-modulated-terahertz-light-detection-using-fast-terahertz-quantum-well-photodetectors
#4
Hua Li, Wen-Jian Wan, Zhi-Yong Tan, Zhang-Long Fu, Hai-Xia Wang, Tao Zhou, Zi-Ping Li, Chang Wang, Xu-Guang Guo, Jun-Cheng Cao
The fast detection of terahertz radiation is of great importance for various applications such as fast imaging, high speed communications, and spectroscopy. Most commercial products capable of sensitively responding the terahertz radiation are thermal detectors, i.e., pyroelectric sensors and bolometers. This class of terahertz detectors is normally characterized by low modulation frequency (dozens or hundreds of Hz). Here we demonstrate the first fast semiconductor-based terahertz quantum well photodetectors by carefully designing the device structure and microwave transmission line for high frequency signal extraction...
June 14, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28614346/semiconductor-based-plasmonic-interferometers-for-ultrasensitive-sensing-in-a-terahertz-regime
#5
Youqiao Ma, Yousef Alattar, Jun Zhou, Mohamed Eldlio, Hiroshi Maeda, Jaromír Pištora, Michael Cada
A robust plasmonic semiconductor-based Mach-Zehnder interferometer (MZI), which consists of a semiconductor layer with a microslit flanked by two identical microgrooves, is proposed and investigated for the terahertz sensing. The microgrooves reflect the surface plasmon polariton waves toward the microslit, where they interfere with the transmitted terahertz wave. The interference pattern is determined by the permittivities of the sensing material and semiconductor (i.e., temperature dependent), making the structure useful for the refractive index (RI) and temperature detection...
June 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28614320/floquet-control-of-dipolaritons-in-quantum-wells
#6
O Kyriienko, O V Kibis, I A Shelykh
We developed the theory of dipolaritons in semiconductor quantum wells irradiated by an off-resonant electromagnetic wave (dressing field). Solving the Floquet problem for the dressed dipolaritons, we demonstrated that the field drastically modifies all dipolaritonic properties. In particular, the dressing field strongly affects the terahertz emission from the considered system. The described effect paves the way for optical control of prospective dipolariton-based terahertz devices.
June 15, 2017: Optics Letters
https://www.readbyqxmd.com/read/28611402/dynamic-nuclear-polarization-nmr-as-a-new-tool-to-investigate-the-nature-of-organic-compounds-occluded-in-plant-silica-particles
#7
Armand Masion, Anne Alexandre, Fabio Ziarelli, Stéphane Viel, Guaciara M Santos
The determination of the chemical nature of the organic matter associated with phytoliths remains a challenge. This difficulty mainly stems from amounts of organic carbon (C) that are often well below the detection limit of traditional spectroscopic tools. Conventional solid-state (13)C Nuclear Magnetic Resonance (NMR) is widely used to examine the nature and structure of organic molecules, but its inherent low sensitivity prohibits the observation of diluted samples. The recent advent of commercial microwave source in the terahertz range triggered a renewed interest in the Dynamic Nuclear Polarization (DNP) technique to improve the signal to noise ratio of solid-state NMR experiments...
June 13, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28605686/solid-state-cocrystal-formation-between-acyclovir-and-fumaric-acid-terahertz-and-raman-vibrational-spectroscopic-studies
#8
Qiang Cai, Jiadan Xue, Qiqi Wang, Yong Du
The vibrational spectra of solid-state acyclovir, fumaric acid and their cocrystal have been investigated by using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. In experimental THz spectra, the cocrystal has absorption peaks in 0.65, 0.94 and 1.10THz respectively, while the raw materials are absolutely different in this region. Raman spectra also show similar results about differences between the cocrystal and raw materials. Density functional theory (DFT) was performed to simulate vibrational modes of different theoretical forms between acyclovir and fumaric acid...
June 9, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/28603011/a-comprehensive-spectroscopic-study-of-the-polymorphs-of-diflunisal-and-their-phase-transformations
#9
Anuradha R Pallipurath, Francesco Civati, Juraj Sibik, Clare Crowley, J Axel Zeitler, Patrick McArdle, Andrea Erxleben
Understanding phase transitions in pharmaceutical materials is of vital importance for drug manufacturing, processing and storage. In this paper we have carried out comprehensive high-resolution spectroscopic studies on the polymorphs of the non-steroidal anti-inflammatory drug diflunisal that has four known polymorphs, forms I-IV (FI-FIV), three of which have known crystal structures. Phase transformations during milling, heating, melt-quenching and exposure to high relative humidity were investigated using Raman and terahertz spectroscopy in combination with differential scanning calorimetry and X-ray powder diffraction...
June 8, 2017: International Journal of Pharmaceutics
https://www.readbyqxmd.com/read/28598444/pumping-approximately-integrable-systems
#10
Florian Lange, Zala Lenarčič, Achim Rosch
Weak perturbations can drive an interacting many-particle system far from its initial equilibrium state if one is able to pump into degrees of freedom approximately protected by conservation laws. This concept has for example been used to realize Bose-Einstein condensates of photons, magnons and excitons. Integrable quantum systems, like the one-dimensional Heisenberg model, are characterized by an infinite set of conservation laws. Here, we develop a theory of weakly driven integrable systems and show that pumping can induce large spin or heat currents even in the presence of integrability breaking perturbations, since it activates local and quasi-local approximate conserved quantities...
June 9, 2017: Nature Communications
https://www.readbyqxmd.com/read/28590485/intermolecular-charge-fluxes-and-far-infrared-spectral-intensities-of-liquid-formamide
#11
Hajime Torii
The intensity generation mechanisms of the far-infrared (far-IR) [or terahertz (THz)] spectrum of liquid formamide, particularly with regard to the behavior of electrons induced by modulations of the hydrogen-bonding conditions of the molecules, are examined theoretically. The theoretical analysis is done in the following two steps. First, density functional theory (DFT) calculations are carried out for the dimers and larger clusters of formamide to analyze the change in the dipole derivative (the square of which is proportional to the IR intensity) induced by hydrogen-bond formation...
June 7, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28590254/reconfigurable-metamaterials-for-terahertz-wave-manipulation
#12
Mohammed Reza Hashemi, Semih Cakmakyapan, Mona Jarrahi
Reconfigurable metamaterials have emerged as promising platforms for manipulating the spectral and spatial properties of terahertz waves without being limited by the characteristics of naturally existing materials. Here, we present a comprehensive overview of various types of reconfigurable metamaterials that are utilized to manipulate the intensity, phase, polarization, and propagation direction of terahertz waves. We discuss various reconfiguration mechanisms based on optical, electrical, thermal, and mechanical stimuli while using semiconductors, superconductors, phase-change materials, graphene, and electromechanical structures...
June 7, 2017: Reports on Progress in Physics
https://www.readbyqxmd.com/read/28589627/benzothiazolium-single-crystals-a-new-class-of-nonlinear-optical-crystals-with-efficient-thz-wave-generation
#13
Seung-Heon Lee, Jian Lu, Seung-Jun Lee, Jae-Hyun Han, Chan-Uk Jeong, Seung-Chul Lee, Xian Li, Mojca Jazbinšek, Woojin Yoon, Hoseop Yun, Bong Joo Kang, Fabian Rotermund, Keith A Nelson, O-Pil Kwon
Highly efficient nonlinear optical organic crystals are very attractive for various photonic applications including terahertz (THz) wave generation. Up to now, only two classes of ionic crystals based on either pyridinium or quinolinium with extremely large macroscopic optical nonlinearity have been developed. This study reports on a new class of organic nonlinear optical crystals introducing electron-accepting benzothiazolium, which exhibit higher electron-withdrawing strength than pyridinium and quinolinium in benchmark crystals...
June 7, 2017: Advanced Materials
https://www.readbyqxmd.com/read/28588202/terahertz-electromagnetic-fences-on-a-graphene-surface-plasmon-polariton-platform
#14
Xidong Wu, Xiang Guo
Controlling the loss of graphene can be used in the field of transformation optics. We propose a new concept of electromagnetic fence on a monolayer graphene surface plasmon polariton platform. Using a Dot-Density-Renderer quasicrystal metasurface, we can simulate the absorption of gradient index optics structures. Numerical simulations show that the incident waves to our designed electromagnetic fence are trapped toward the central lines and quickly absorbed by the high-loss region. Two basic types of electromagnetic fence and its composite structures have been designed and analyzed, which exhibit excellent broadband absorbing performances at 8 THz-12 THz...
June 6, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28581810/coherent-two-dimensional-terahertz-magnetic-resonance-spectroscopy-of-collective-spin-waves
#15
Jian Lu, Xian Li, Harold Y Hwang, Benjamin K Ofori-Okai, Takayuki Kurihara, Tohru Suemoto, Keith A Nelson
We report a demonstration of two-dimensional (2D) terahertz (THz) magnetic resonance spectroscopy using the magnetic fields of two time-delayed THz pulses. We apply the methodology to directly reveal the nonlinear responses of collective spin waves (magnons) in a canted antiferromagnetic crystal. The 2D THz spectra show all of the third-order nonlinear magnon signals including magnon spin echoes, and 2-quantum signals that reveal pairwise correlations between magnons at the Brillouin zone center. We also observe second-order nonlinear magnon signals showing resonance-enhanced second-harmonic and difference-frequency generation...
May 19, 2017: Physical Review Letters
https://www.readbyqxmd.com/read/28580930/cascaded-spintronic-logic-with-low-dimensional-carbon
#16
Joseph S Friedman, Anuj Girdhar, Ryan M Gelfand, Gokhan Memik, Hooman Mohseni, Allen Taflove, Bruce W Wessels, Jean-Pierre Leburton, Alan V Sahakian
Remarkable breakthroughs have established the functionality of graphene and carbon nanotube transistors as replacements to silicon in conventional computing structures, and numerous spintronic logic gates have been presented. However, an efficient cascaded logic structure that exploits electron spin has not yet been demonstrated. In this work, we introduce and analyse a cascaded spintronic computing system composed solely of low-dimensional carbon materials. We propose a spintronic switch based on the recent discovery of negative magnetoresistance in graphene nanoribbons, and demonstrate its feasibility through tight-binding calculations of the band structure...
June 5, 2017: Nature Communications
https://www.readbyqxmd.com/read/28580778/full-state-controls-of-terahertz-waves-using-tensor-coding-metasurfaces
#17
Shuo Liu, Hao Chi Zhang, Lei Zhang, Quan Long Yang, Quan Xu, Jianqiang Gu, Yan Yang, Xiao Yang Zhou, Jiaguang Han, Qiang Cheng, Weili Zhang, Tie Jun Cui
Coding metasurfaces allow us to study metamaterials from a fully digital perspective, enabling many exotic functionalities, such as anomalous reflections, broadband diffusions, and polarization conversion. Here, we propose a tensor coding metasurface at terahertz (THz) frequency that could take full-state controls of an electromagnetic wave in terms of its polarization state, phase and amplitude distributions, and wave-vector mode. Owing to the off-diagonal elements that dominant in the reflection matrix, each coding particle could reflect the normally incident wave to its cross-polarization with controllable phases, resulting in different coding digits...
June 15, 2017: ACS Applied Materials & Interfaces
https://www.readbyqxmd.com/read/28578422/three-dimensional-anisotropic-metamaterials-as-triaxial-optical-inclinometers
#18
Kriti Agarwal, Chao Liu, Daeha Joung, Hyeong-Ryeol Park, Sang-Hyun Oh, Jeong-Hyun Cho
Split-ring resonators (SRRs) present an attractive avenue for the development of micro/nano scale inclinometers for applications like medical microbots, military hardware, and nanosatellite systems. However, the 180° isotropy of their two-dimensional structure presents a major hurdle. In this paper, we present the design of a three-dimensional (3D) anisotropic SRR functioning as a microscale inclinometer enabling it to remotely sense rotations from 0° to 360° along all three axes (X, Y, and Z), by employing the geometric property of a 3D structure...
June 2, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28575817/terahertz-acoustic-phonon-detection-from-a-compact-surface-layer-of-spherical-nanoparticles-powder-mixture-of-aluminum-alumina-and-multi-walled-carbon-nanotube
#19
A Abouelsayed, M R Ebrahim, W El Hotaby, S A Hassan, Emad Al-Ashkar
We present terahertz spectroscopy study on spherical nanoparticles powder mixture of aluminum, alumina, and MWCNTs induced by surface mechanical attrition treatment (SMAT) of aluminum substrates. Surface alloying of AL, Al2O3 0.95% and MWCNTs 0.05% powder mixture was produced during SMAT process, where a compact surface layer of about 200 μm due to ball bombardment was produced from the mixture. Al2O3 alumina powder played a significant role in MWCNTs distribution on surface, those were held in deformation surface cites of micro-cavities due to SMAT process of Al...
May 25, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
https://www.readbyqxmd.com/read/28571462/analysis-of-granular-packing-structure-by-scattering-of-thz-radiation
#20
Philip Born, Karsten Holldack
Scattering methods are widely used to characterize the structure and constituents of matter on small length scales. This motivates this introductory text on identifying prospective approaches to scattering-based methods for granular media. A survey to light scattering by particles and particle ensembles is given. It is elaborated why the established scattering methods using X-rays and visible light cannot in general be transferred to granular media. Spectroscopic measurements using terahertz radiation are highlighted as they probe the scattering properties of granular media, which are sensitive to the packing structure...
May 2017: Review of Scientific Instruments
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