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Debasish Das Mahanta, Rajib Kumar Mitra, Nirnay Samanta
Many biologically important processes involve a subtle interplay between Columbic and hydrophobic interactions among molecular groups with water. A comprehensive understanding of such processes, specially while occurring simultaneously in the same molecule is of practical importance. In this contribution we report the ultrafast (sub-ps to ps) collective hydrogen bond dynamics of water in the extended hydration layers in a series of alkylammonium chloride salts using THz time domain spectroscopic (TTDS) technique (0...
July 25, 2017: Journal of Physical Chemistry. B
Kensuke Sasaki, Maya Mizuno, Kanako Wake, Soichi Watanabe
In this study, we present an assessment of human-body exposure to an electromagnetic eld at frequencies ranging from 10 GHz to 1 THz. The energy absorption and temperature elevation were assessed by solving boundary value problems of the one-dimensional Maxwell equations and a bioheat equation for a multilayer plane model. Dielectric properties were measured in vitro at frequencies of up to 1 THz at body temperature. A Monte Carlo simulation was conducted to assess variations of the transmittance into a skin surface and temperature elevation inside a body by considering the variation of the tissue thickness due to individual differences among human bodies...
July 25, 2017: Physics in Medicine and Biology
Amin Soltani, Denis Gebauer, Lennart Duschek, Bernd Fischer, Helmut Cölfen, Martin Koch
Crystal formation is a highly debated problem. We show that the crystallization of L-(+)-tartaric acid from water follows a non-classical path involving intermediate hydrated states. Analytical ultracentrifugation indicates solution clusters of the initial stages aggregate to form an early intermediate. Terahertz spectroscopy performed during water evaporation highlights a transient increase in the absorption during nucleation. This indicates the recurrence of water molecules which are expelled from the intermediate phase...
July 23, 2017: Chemistry: a European Journal
Liang Wu, Jinglong Liu, Hui Li, Chunfeng Ding, Ningning Xu, Xiaolei Zhao, Zongcheng Xu, Quan Sheng, Jianquan Yao, Jining Li, Xin Ding, Weili Zhang
The dielectric properties of an active KTaO3 hybrid metamaterial structure and its tunability under external electric fields are investigated at room temperature by means of terahertz time-domain spectroscopy. Application of the electric field leads to an appreciable tuning of the dielectric loss, which is up to 17%. Meanwhile, the refractive index also changes appreciably. These findings are attributed to the internal space charge field in the crystal caused by the excited free carriers.
July 20, 2017: Scientific Reports
Rajind Mendis, Masaya Nagai, Wei Zhang, Daniel M Mittleman
We demonstrate a simple and effective strategy for implementing a polarizing beamsplitter for the terahertz spectral region, based on an artificial dielectric medium that is scalable to a range of desired frequencies. The artificial dielectric medium consists of a uniformly spaced stack of metal plates, which is electromagnetically equivalent to a stacked array of parallel-plate waveguides. The operation of the device relies on both the lowest-order, transverse-electric and transverse-magnetic modes of the parallel-plate waveguide...
July 19, 2017: Scientific Reports
Lei Cao, Qiang Fu, Bang Wu, Yongqian Xiong
The high electron concentration in GaN-based heterostructures necessitate the consideration of nonlocal corrections in the magnetoconductivity for the study of magnetoplasmon-polaritons (MPPs) in the lossy two dimensional electron gas (2DEG) system with grating couplers. With the complete set of Maxwell equations, the complex dispersion frequency and absorption spectrum are calculated numerically at different magnetic field (B<sub>max</sub> = 10 T) and plasmon wavevectors (k<sub>max</sub> = 5×10<sup>7</sup> m<sup>-1</sup>)...
July 19, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Andrew J Lee, David J Spence, Helen M Pask
We detail the operation of a THz laser source based on non-linear stimulated polariton scattering (SPS) in Mg:LiNbO<sub>3</sub>. This system utilizes a fundamental wavelength of 1342 nm to completely avoid the negative effect of free-carrier generation within high-resistivity silicon (Si) prisms used to extract THz radiation from the Mg:LiNbO<sub>3</sub> crystal. THz power of up to 23.6 μW (62.3 μW when chopped at 50% duty cycle) was detected at 1.33 THz, and frequency tunability across the range 1...
July 15, 2017: Optics Letters
Marco P Fischer, Johannes Bühler, Gabriel Fitzky, Takayuki Kurihara, Stefan Eggert, Alfred Leitenstorfer, Daniele Brida
We experimentally demonstrate tunable, phase-matched difference frequency generation covering the spectral region below 15 THz using 4H-SiC as a nonlinear crystal. This material combines a non-centrosymmetric lattice and strong birefringence with broadband transparency at low optical frequencies. Thorough refractive index measurements in the terahertz spectral range allow us to calculate phase-matching conditions for any near-infrared pump laser source. 4H-SiC is also exploited as a detector crystal for electro-optic sampling...
July 15, 2017: Optics Letters
Sen Mou, Andrea Rubano, Domenico Paparo
Ionic liquids are salts found in their liquid state at ambient temperature. The physicochemical properties of ionic liquids can be tailored by selecting constituent cation and anion from numerous available ions. The physicochemical properties can be further tuned by mixing different neat ionic liquids. Reported data of ionic liquid mixtures reveal that frequently investigated properties such as density, viscosity and thermal stability follow corresponding mixing laws. Complex permittivity in the interval of terahertz frequencies is of great importance to understand the molecular interactions and the solvation dynamics which drive the macroscopic properties of ionic liquids, however, to the best of our knowledge, there are scarce reports about the mixing behavior of complex permittivity in ionic liquid mixtures...
July 13, 2017: Journal of Physical Chemistry. B
L Zhu, Y Huang, Z Yao, B Quan, L Zhang, J Li, C Gu, X Xu, Z Ren
Improving terahertz (THz) emission from graphene is a challenge for graphene-based THz photonics as graphene demonstrates a weak light-matter interaction. With a unique ultra-black surface structure, vertically grown graphene (VGG) is proposed to enhance the light-matter interaction and further enhance THz emission. Herein, enhanced THz radiation is observed by THz time-domain emission spectroscopy from VGG compared with single-layer graphene. The radiated THz amplitude shows a linear dependence on pump power, which demonstrates a second order nonlinear effect...
July 27, 2017: Nanoscale
Yi Zou, Jiang Li, Yiyuan Cui, Peiren Tang, Lianghui Du, Tunan Chen, Kun Meng, Qiao Liu, Hua Feng, Jianheng Zhao, Mina Chen, Li-Guo Zhu
While myelin deficit of the central nervous system leads to several severe diseases, the definitive diagnostic means are lacking. We proposed and performed terahertz time-domain spectroscopy (THz-TDS) combined with chemometric techniques to discriminate and evaluate the severity of myelin deficit in mouse and rhesus monkey brains. The THz refractive index and absorption coefficient of paraffin-embedded brain tissues from both normal and mutant dysmyelinating mice are shown. Principal component analysis of time-domain THz signal (PCA-tdTHz) and absorption-refractive index relation of THz spectrum identified myelin deficit without exogenous labeling or any pretreatment...
July 12, 2017: Scientific Reports
Qiushuo Sun, Edward P J Parrott, Yuezhi He, Emma Pickwell-Macpherson
In vivo terahertz (THz) imaging of human skin needs to be done in reflection geometry due to the high attenuation of THz light by water in the skin. To aid the measurement procedure, there is typically an imaging window onto which the patient places the area of interest. The window enables better pulse alignment and helps keep the patient correctly positioned during the measurement. In this paper we demonstrate how the occlusion caused by the skin contact with the imaging window during the measurement affects the THz response...
July 12, 2017: Journal of Biophotonics
Teresa Mildred Dierks, Timothy Michael Korter
The hygroscopicity of solid sorbitol is important for its utilization as a sweetener in the pharmaceutical and food industries. The molecular foundations of sorbitol hydration characteristics are explored here using two solvated cocrystals, sorbitol-water and sorbitol-pyridine. In this work, solid-state density functional theory and terahertz time-domain spectroscopy were used to evaluate the relative stabilities of these cocrystals as compared to anhydrous sorbitol in terms of conformational and cohesive energies...
July 12, 2017: Journal of Physical Chemistry. A
Sean Knight, Tino Hofmann, Chamseddine Bouhafs, Nerijus Armakavicius, Philipp Kühne, Vallery Stanishev, Ivan G Ivanov, Rositsa Yakimova, Shawn Wimer, Mathias Schubert, Vanya Darakchieva
Unraveling the doping-related charge carrier scattering mechanisms in two-dimensional materials such as graphene is vital for limiting parasitic electrical conductivity losses in future electronic applications. While electric field doping is well understood, assessment of mobility and density as a function of chemical doping remained a challenge thus far. In this work, we investigate the effects of cyclically exposing epitaxial graphene to controlled inert gases and ambient humidity conditions, while measuring the Lorentz force-induced birefringence in graphene at Terahertz frequencies in magnetic fields...
July 11, 2017: Scientific Reports
Matthew R Ryder, Ben Van de Voorde, Bartolomeo Civalleri, Thomas D Bennett, Sanghamitra Mukhopadhyay, Gianfelice Cinque, Felix Fernandez-Alonso, Dirk De Vos, Svemir Rudić, Jin-Chong Tan
We show clear experimental evidence of cooperative terahertz (THz) dynamics observed below 3 THz (∼100  cm^{-1}), for a low-symmetry Zr-based metal-organic framework structure, termed MIL-140A [ZrO(O_{2}C-C_{6}H_{4}-CO_{2})]. Utilizing a combination of high-resolution inelastic neutron scattering and synchrotron radiation far-infrared spectroscopy, we measured low-energy vibrations originating from the hindered rotations of organic linkers, whose energy barriers and detailed dynamics have been elucidated via ab initio density functional theory calculations...
June 23, 2017: Physical Review Letters
José Francisco Algorri, Braulio García-Cámara, Alexander Cuadrado, José Manuel Sánchez-Pena, Ricardo Vergaz
Dielectric metasurfaces based on high refractive index materials have been proposed recently. This type of structure has several advantages over their metallic counterparts. In this work, we demonstrate that dielectric metasurfaces can be theoretically designed satisfying Kerker's zero-forward condition. This is the first time that a dielectric metasurface based on this principle has been designed. A selective dielectric metasurface of silicon nanopillars is designed to work at 632.8 nm. This structure could work both as a dielectric mirror and a reject band filter...
July 7, 2017: Nanomaterials
Zhi Li, Weidong Chen, Feiyu Lian, Hongyi Ge, Aihong Guan
No abstract text is available yet for this article.
January 1, 2017: Applied Spectroscopy
Hai-Mu Ye, Han Li, Shu-Fang Yao
No abstract text is available yet for this article.
January 1, 2017: Applied Spectroscopy
S Gerber, S-L Yang, D Zhu, H Soifer, J A Sobota, S Rebec, J J Lee, T Jia, B Moritz, C Jia, A Gauthier, Y Li, D Leuenberger, Y Zhang, L Chaix, W Li, H Jang, J-S Lee, M Yi, G L Dakovski, S Song, J M Glownia, S Nelson, K W Kim, Y-D Chuang, Z Hussain, R G Moore, T P Devereaux, W-S Lee, P S Kirchmann, Z-X Shen
The interactions that lead to the emergence of superconductivity in iron-based materials remain a subject of debate. It has been suggested that electron-electron correlations enhance electron-phonon coupling in iron selenide (FeSe) and related pnictides, but direct experimental verification has been lacking. Here we show that the electron-phonon coupling strength in FeSe can be quantified by combining two time-domain experiments into a "coherent lock-in" measurement in the terahertz regime. X-ray diffraction tracks the light-induced femtosecond coherent lattice motion at a single phonon frequency, and photoemission monitors the subsequent coherent changes in the electronic band structure...
July 7, 2017: Science
Matthew Swithenbank, Andrew D Burnett, Christopher Russell, Lianhe H Li, Alexander Giles Davies, Edmund H Linfield, John E Cunningham, Christopher D Wood
Terahertz-frequency-range measurements can offer potential insight into the picosecond dynamics, and therefore function, of many chemical systems. There is a need to develop technologies capable of performing such measurements in aqueous and polar environments, particularly when it is necessary to maintain the full functionality of biological samples. In this study, we present a proof-of-concept technology comprising an on-chip planar Goubau line, integrated with a microfluidic channel, which is capable of low-loss, terahertz-frequency-range spectroscopic measurements of liquids...
July 20, 2017: Analytical Chemistry
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