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Terahertz

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https://www.readbyqxmd.com/read/27928130/application-of-terahertz-attenuated-total-reflection-spectroscopy-to-detect-changes-in-the-physical-properties-of-lactose-during-the-lubrication-process-required-for-drug-formulation
#1
Masafumi Dohi, Wataru Momose, Kazunari Yamashita, Tadashi Hakomori, Shusaku Sato, Shuji Noguchi, Katsuhide Terada
Manufacturing the solid dosage form of an orally administered drug requires lubrication to enhance manufacturability, ensuring that critical quality attributes such as disintegration and dissolution of the drug product are maintained during manufacture. Here, to evaluate lubrication performance during manufacture, we used terahertz attenuated total reflection (THz-ATR) spectroscopy to detect differences in the physical characteristics of the lubricated powder. We applied a simple formulation prepared by blending granulated lactose as filler with magnesium stearate as lubricant...
December 6, 2016: Chemical & Pharmaceutical Bulletin
https://www.readbyqxmd.com/read/27924939/subwavelength-insb-based-slot-wavguides-for-thz-transport-concept-and-practical-implementations
#2
Youqiao Ma, Jun Zhou, Jaromír Pištora, Mohamed Eldlio, Nghia Nguyen-Huu, Hiroshi Maeda, Qiang Wu, Michael Cada
Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ(2)/530) in the THz spectral range...
December 7, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27917930/strongly-confined-spoof-surface-plasmon-polaritons-waveguiding-enabled-by-planar-staggered-plasmonic-waveguides
#3
Longfang Ye, Yifan Xiao, Yanhui Liu, Liang Zhang, Guoxiong Cai, Qing Huo Liu
We demonstrate a novel route to achieving highly efficient and strongly confined spoof surface plasmon polaritons (SPPs) waveguides at subwavelength scale enabled by planar staggered plasmonic waveguides (PSPWs). The structure of these new waveguides consists of an ultrathin metallic strip with periodic subwavelength staggered double groove arrays supported by a flexible dielectric substrate, leading to unique staggered EM coupling and waveguiding phenomenon. The spoof SPP propagation properties, including dispersion relations and near field distributions, are numerically investigated...
December 5, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27916999/high-power-telecommunication-compatible-photoconductive-terahertz-emitters-based-on-plasmonic-nano-antenna-arrays
#4
Nezih Tolga Yardimci, Hong Lu, Mona Jarrahi
We present a high-power and broadband photoconductive terahertz emitter operating at telecommunication optical wavelengths, at which compact and high-performance fiber lasers are commercially available. The presented terahertz emitter utilizes an ErAs:InGaAs substrate to achieve high resistivity and short carrier lifetime characteristics required for robust operation at telecommunication optical wavelengths. It also uses a two-dimensional array of plasmonic nano-antennas to offer significantly higher optical-to-terahertz conversion efficiencies compared to the conventional photoconductive emitters, while maintaining broad operation bandwidths...
November 7, 2016: Applied Physics Letters
https://www.readbyqxmd.com/read/27914448/a-fractional-calculus-model-of-anomalous-dispersion-of-acoustic-waves
#5
Andrew W Wharmby
An empirical formula based on viscoelastic analysis techniques that employs concepts from the fractional calculus that was used to model the dielectric behavior of materials exposed to oscillating electromagnetic fields in the radiofrequency, terahertz, and infrared bands. This work adapts and applies the formula to model viscoelastic behavior of materials that show an apparent increase of phase velocity of vibration with an increase in frequency, otherwise known as anomalous dispersion. A fractional order wave equation is derived through the application of the classic elastic-viscoelastic correspondence principle whose analytical solution is used to describe absorption and dispersion of acoustic waves in the viscoelastic material displaying anomalous dispersion in a specific frequency range...
September 2016: Journal of the Acoustical Society of America
https://www.readbyqxmd.com/read/27906313/experimental-study-on-the-transition-of-plasmonic-resonance-modes-in-double-ring-dimers-by-conductive-junctions-in-the-terahertz-regime
#6
Huifang Zhang, Chun Li, Caihong Zhang, Xueqian Zhang, Jianqiang Gu, Biaobing Jin, Jiaguang Han, Weili Zhang
Plasmonic dimers that made from two subwavelength particles have drawn much attention in the recent years, which are quite promising in local field enhancement, sensing, high frequency conductance probing and electron tunneling. In this work, we experimentally investigate the mode transition effect of different plasmonic resonances in double-ring dimers when introducing conductive junction at the dimer gap in the terahertz regime. Without the junction, the dimers support a single dipolar bonding dimer plasmonic (BDP) mode...
November 28, 2016: Optics Express
https://www.readbyqxmd.com/read/27906290/polarization-variable-emitter-for-terahertz-time-domain-spectroscopy
#7
Dmitry S Bulgarevich, Makoto Watanabe, Mitsuharu Shiwa, Gudrun Niehues, Hideaki Kitahara, Masahiko Tani
We report on the progress in the development of linear polarization-variable multi-electrode emitters for terahertz time-domain spectroscopy. The results on its microfabrication, the finite element method modeling of appropriate bias distribution between electrodes, the finite-difference time-domain simulated spectral output, and actual experimental testing are presented. The rotation of the emitted terahertz field with linear polarization on an angle multiple of 45° can be achieved by synchronized bias and single polarizer rotations...
November 28, 2016: Optics Express
https://www.readbyqxmd.com/read/27906247/broadband-polarizers-based-on-graphene-metasurfaces
#8
Tianjing Guo, Christos Argyropoulos
We present terahertz metasurfaces based on aligned rectangular graphene patches placed on top of a dielectric layer to convert the transmitted linearly polarized waves to circular or elliptical polarized radiation. Our results lead to the design of an ultrathin broadband terahertz quarter-wave plate. In addition, ultrathin metasurfaces based on the arrays of L-shaped graphene periodic patches are demonstrated to achieve broadband cross-polarization transformation in reflection and transmission. The proposed metasurface designs have tunable responses and are envisioned to become the building blocks of several integrated terahertz systems...
December 1, 2016: Optics Letters
https://www.readbyqxmd.com/read/27905563/coherent-excitation-of-optical-phonons-in-gaas-by-broadband-terahertz-pulses
#9
Zhengping Fu, Masashi Yamaguchi
Coherent excitation and control of lattice motion by electromagnetic radiation in optical frequency range has been reported through variety of indirect interaction mechanisms with phonon modes. However, coherent phonon excitation by direct interaction of electromagnetic radiation and nuclei has not been demonstrated experimentally in terahertz (THz) frequency range mainly due to the lack of THz emitters with broad bandwidth suitable for the purpose. We report the experimental observation of coherent phonon excitation and detection in GaAs using ultrafast THz-pump/optical-probe scheme...
December 1, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27901070/low-frequency-piezoresonance-defined-dynamic-control-of-terahertz-wave-propagation
#10
Moumita Dutta, Soutik Betal, Xomalin G Peralta, Amar S Bhalla, Ruyan Guo
Phase modulators are one of the key components of many applications in electromagnetic and opto-electric wave propagations. Phase-shifters play an integral role in communications, imaging and in coherent material excitations. In order to realize the terahertz (THz) electromagnetic spectrum as a fully-functional bandwidth, the development of a family of efficient THz phase modulators is needed. Although there have been quite a few attempts to implement THz phase modulators based on quantum-well structures, liquid crystals, or meta-materials, significantly improved sensitivity and dynamic control for phase modulation, as we believe can be enabled by piezoelectric-resonance devices, is yet to be investigated...
November 30, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27896010/freeze-thaw-hysteresis-effects-in-terahertz-imaging-of-biomedical-tissues
#11
Yuezhi He, Benjamin S-Y Ung, Edward P J Parrott, Anil T Ahuja, Emma Pickwell-MacPherson
There have recently been several studies published involving terahertz (THz) imaging of frozen biomedical samples. In this paper, we investigate the effects of the freeze-thaw cycle on THz properties of porcine muscle and fat samples. For ordinary freezing, there was a significant change in the THz properties after thawing for muscle tissue but not for fat tissue. However, if snap-freezing was combined with fast-thawing instead of ordinary freezing and ordinary thawing, then the freeze-thaw hysteresis was removed...
November 1, 2016: Biomedical Optics Express
https://www.readbyqxmd.com/read/27895988/terahertz-identification-and-quantification-of-neurotransmitter-and-neurotrophy-mixture
#12
Yan Peng, Xiaorong Yuan, Xiang Zou, Wanqing Chen, Hui Huang, Hongwei Zhao, Bo Song, Liang Chen, Yiming Zhu
Terahertz spectroscopy has been widely used for investigating the fingerprint spectrum of different substances. For cancerous tissues, the greatest difficulty is the absorption peaks of various substances contained in tissues overlap with each other, which are hard to identify and quantitative analyze. As a result, it is very hard to measure the presence of cancer cell and then to diagnose accurately. In this paper, we select three typical neurotransmitters (γ-aminobutyric acid, L-glutamic acid, dopamine hydrochloride) and two typical metabolites (inositol and creatine) in neurons to measure their terahertz spectra with different mixture ratios...
November 1, 2016: Biomedical Optics Express
https://www.readbyqxmd.com/read/27893724/polaritons-in-layered-two-dimensional-materials
#13
REVIEW
Tony Low, Andrey Chaves, Joshua D Caldwell, Anshuman Kumar, Nicholas X Fang, Phaedon Avouris, Tony F Heinz, Francisco Guinea, Luis Martin-Moreno, Frank Koppens
In recent years, enhanced light-matter interactions through a plethora of dipole-type polaritonic excitations have been observed in two-dimensional (2D) layered materials. In graphene, electrically tunable and highly confined plasmon-polaritons were predicted and observed, opening up opportunities for optoelectronics, bio-sensing and other mid-infrared applications. In hexagonal boron nitride, low-loss infrared-active phonon-polaritons exhibit hyperbolic behaviour for some frequencies, allowing for ray-like propagation exhibiting high quality factors and hyperlensing effects...
November 28, 2016: Nature Materials
https://www.readbyqxmd.com/read/27892566/water-transport-within-carbon-nanotubes-on-a-wave
#14
Jin-Yi Li, Zeng-Qiang Wu, Jing-Juan Xu, Hong-Yuan Chen, Xing-Hua Xia
Water molecules possess discontinuous properties in confined surroundings as compared to the bulk, their transport velocity shows a step change with the increase in the radius of hydrophobic carbon nanotubes (CNTs). Here, we report that the chain of water molecules in CNTs behaves as a "spring" owing to hydrogen bonding. Thus, the transport of water molecules in confined systems proceeds as a wave motion with eigen frequencies in the terahertz region which is determined by the CNT size. Water velocities derived from molecular dynamics (MD) fit well with the ones from finite element methods (FEM) on consideration of both the no-slip and slip boundary conditions for CNT diameters less than 1 nm and more than 1 nm, respectively...
November 28, 2016: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/27886470/stability-of-high-density-two-dimensional-excitons-against-a-mott-transition-in-high-magnetic-fields-probed-by-coherent-terahertz-spectroscopy
#15
Qi Zhang, Yongrui Wang, Weilu Gao, Zhongqu Long, John D Watson, Michael J Manfra, Alexey Belyanin, Junichiro Kono
We have performed time-resolved terahertz absorption measurements on photoexcited electron-hole pairs in undoped GaAs quantum wells in magnetic fields. We probed both unbound- and bound-carrier responses via cyclotron resonance and intraexciton resonance, respectively. The stability of excitons, monitored as the pair density was systematically increased, was found to dramatically increase with increasing magnetic field. Specifically, the 1s-2p_{-} intraexciton transition at 9 T persisted up to the highest density, whereas the 1s-2p feature at 0 T was quickly replaced by a free-carrier Drude response...
November 11, 2016: Physical Review Letters
https://www.readbyqxmd.com/read/27886232/amplification-of-resonant-field-enhancement-by-plasmonic-lattice-coupling-in-metallic-slit-arrays
#16
Pernille Klarskov, Abebe T Tarekegne, Krzysztof Iwaszczuk, X-C Zhang, Peter Uhd Jepsen
Nonlinear spectroscopic investigation in the terahertz (THz) range requires significant field strength of the light fields. It is still a challenge to obtain the required field strengths in free space from table-top laser systems at sufficiently high repetition rates to enable quantitative nonlinear spectroscopy. It is well known that local enhancement of the THz field can be obtained for instance in narrow apertures in metallic films. Here we show by simulation, analytical modelling and experiment that the achievable field enhancement in a two-dimensional array of slits with micrometer dimensions in a metallic film can be increased by at least 60% compared to the enhancement in an isolated slit...
November 25, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27883067/all-optical-thz-wave-switching-based-on-ch3nh3pbi3-perovskites
#17
Kyu-Sup Lee, Rira Kang, Byungwoo Son, Dong-Yu Kim, Nan Ei Yu, Do-Kyeong Ko
Hybrid structures of silicon with organic-inorganic perovskites are proposed for optically controllable switching of terahertz (THz) waves over a broad spectral range from 0.2 to 2THz. A 532-nm external laser was utilized to generate photoexcited free carriers at the devices and consequentially to control the terahertz amplitude modulation, obtaining a depth of up to 68% at a laser irradiance of 1.5 W/cm(2). In addition, we compared the performances from three types of perovskite devices fabricated via different solution processing methods and suggested a stable and highly efficient THz switch based on a one-step processing...
November 24, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27876881/high-acquisition-rate-single-shot-pump-probe-measurements-using-time-stretching-method
#18
Masataka Kobayashi, Yasuo Minami, Courtney L Johnson, Parker D Salmans, Nicholas R Ellsworth, Jun Takeda, Jeremy A Johnson, Ikufumi Katayama
Recent advances of ultrafast spectroscopy allow the capture of an entire ultrafast signal waveform in a single probe shot, which greatly reduces the measurement time and opens the door for the spectroscopy of unrepeatable phenomena. However, most single-shot detection schemes rely on two-dimensional detectors, which limit the repetition rate of the measurement and can hinder real-time visualization and manipulation of signal waveforms. Here, we demonstrate a new method to circumvent these difficulties and to greatly simplify the detection setup by using a long, single-mode optical fiber and a fast photodiode...
November 23, 2016: Scientific Reports
https://www.readbyqxmd.com/read/27869867/detection-and-identification-of-drugs-under-real-conditions-by-using-noisy-terahertz-broadband-pulse
#19
Vyacheslav A Trofimov, Svetlana A Varentsova
We discuss an effective method for detecting and identifying drugs using a high-noise terahertz (THz) signal. We add a noisy THz signal obtained in real conditions to the THz signal transmitted through a sample with the illicit drug methamphetamine. The insufficiency of the standard THz time-domain spectroscopy method is demonstrated, showing that this method detects the spectral features of neutral substances and explosives in a noisy THz signal. The method discussed is based upon time-dependent integral correlation criteria calculated using spectral dynamics of the medium response...
November 20, 2016: Applied Optics
https://www.readbyqxmd.com/read/27862423/active-photoswitching-of-sharp-fano-resonances-in-thz-metadevices
#20
Manukumara Manjappa, Yogesh Kumar Srivastava, Longqing Cong, Ibraheem Al-Naib, Ranjan Singh
Fano resonances offer exciting features in enhancing the non-linearity and sensing capabilities in metamaterial systems. An active photoswitching of Fano resonances in a terahertz metadevice at low optical pump powers is demonstrated, which signifies the extreme sensitivity of the high-quality-factor resonant electric field to the external light illumination.
November 14, 2016: Advanced Materials
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