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Huo Zhang, Zhi Li, Tao Chen, Binyi Qin
Residues of harmful dyes such as Auramine O (AO) in herb and food products threaten the health of people. So, fast and sensitive detection techniques of the residues are needed. As a powerful tool for substance detection, terahertz (THz) spectroscopy was used for the quantitative determination of AO by combining with an improved partial least-squares regression (PLSR) model in this paper. Absorbance of herbal samples with different concentrations was obtained by THz-TDS in the band between 0.2THz and 1.6THz...
May 10, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Ivan Ivanov, Yunbin Hu, Silvio Osella, Uliana Beser, Hai I Wang, David Beljonne, Akimitsu Narita, Klaus Müllen, Dmitry Turchinovich, Mischa Bonn
The effect of edge engineering of graphene nanoribbons (GNRs) on their ultrafast photoconductivity is investigated. Three different GNRs were fabricated by bottom-up synthesis in the liquid phase, where structure, width, and edge planarity could be controlled chemically at the atomic level. The charge carrier transport in the fabricated GNRs was studied on the ultrafast, sub-picosecond time-scale using time-resolved terahertz (THz) spectroscopy, giving access to the elementary parameters of carrier conduction...
May 19, 2017: Journal of the American Chemical Society
K Olejník, V Schuler, X Marti, V Novák, Z Kašpar, P Wadley, R P Campion, K W Edmonds, B L Gallagher, J Garces, M Baumgartner, P Gambardella, T Jungwirth
Antiferromagnets offer a unique combination of properties including the radiation and magnetic field hardness, the absence of stray magnetic fields, and the spin-dynamics frequency scale in terahertz. Recent experiments have demonstrated that relativistic spin-orbit torques can provide the means for an efficient electric control of antiferromagnetic moments. Here we show that elementary-shape memory cells fabricated from a single-layer antiferromagnet CuMnAs deposited on a III-V or Si substrate have deterministic multi-level switching characteristics...
May 19, 2017: Nature Communications
Xu Chen, Wenhui Fan
A planar terahertz metamaterial sensor consisting of a corrugated metal stripe perforated by three rectangular grooves is proposed and investigated numerically. Due to the formation of Fabry-Perot resonance of the spoof surface plasmons mode on the corrugated metal stripe, the extremely sharp resonance in transmission spectrum associated with strong local field enhancement and high quality factor can be realized and exploited for ultrasensitive sensing. Since the intense interaction between electromagnetic waves and analyte materials, the frequency sensitivity of 1...
May 18, 2017: Scientific Reports
M D Thomson, K Rabia, F Meng, M Bykov, S van Smaalen, H G Roskos
Charge density waves (CDWs), i.e. the periodic spatial modulation of coupled electronic and lattice density, are ubiquitous in low-dimensional conductors and have taken on renewed relevance due their role in state-of-the-art materials, e.g. high-T c superconductors, topological insulators and low-dimensional carbon. As CDWs are described by a complex order parameter to represent both the amplitude and phase, they are formally analogous to BCS superconductors and spin-waves, providing a prototype of collective phenomena for the further development of field theories and ab-initio calculations of complex solids...
May 17, 2017: Scientific Reports
Judith Reichenbach, Stuart Ruddell, Mario González-Jiménez, Julio Lemes, David Andrew Turton, David J France, Klaas Wynne
Gigahertz to terahertz frequency infrared and Raman spectra contain a wealth of information concerning the structure, intermolecular forces, and dynamics of ionic liquids. However, these spectra generally have a large number of contributions ranging from slow diffusional modes to underdamped librations, and intramolecular vibrational modes. This makes it difficult to isolate effects such as the role of coulombic and hydrogen-bonding interactions. We have applied far-infrared and ultrafast optical Kerr-effect spectroscopies on carefully selected ions with a greater or lesser degree of symmetry in order to isolate spectral signals of interest...
May 16, 2017: Journal of the American Chemical Society
Alexander P Shkurinov, Anton S Sinko, Peter M Solyankin, Alexander V Borodin, Mikhail N Esaulkov, Vladimir V Annenkov, Igor A Kotelnikov, Igor V Timofeev, Xi-Cheng Zhang
The present paper studies the generation mechanism of terahertz (THz) radiation from tightly focused femtosecond laser pulses in a gas medium. We measured the angular radiation pattern under different focusing conditions and observed that, with the deepening of focus, the angular radiation pattern changes and optical-to-THz conversion efficiency increases. The analysis of the observed phenomena led to the assumption that the dipole radiation prevails in most cases despite the existing conception regarding the dominating role of the quadrupole mechanism of radiation...
April 2017: Physical Review. E
Jérôme Mahé, Daniël J Bakker, Sander Jaeqx, Anouk M Rijs, Marie-Pierre Gaigeot
Vibrational signatures of Ac-Phe-AA-NH2 dipeptides are recorded and analysed in the far IR/THz spectral domain (100-800 cm(-1), 3-24 THz), with the 'AA' amino acid chosen within the series 'AA' = Gly, Ala, Pro, Cys, Ser, Val. Phe stands for phenylalanine. IR-UV ion dip experiments are conducted on the free electron laser FELIX and combined with DFT-based molecular dynamics simulations for the calculation of the dynamical anharmonic vibrational spectra. The excellent agreements between the experimental and theoretical spectra of the Ac-Phe-AA-NH2 series allow us to make detailed and unambiguous mapping of the vibrational motions into three main domains: 700-800 cm(-1) for C-H waggings, 400-700 cm(-1) for N-H waggings, with a one-to-one signature per amide N-H backbone group, 0-400 cm(-1) for delocalized and large amplitude collective motions over the dipeptide backbone, with backbone torsional motions arising <100 cm(-1)...
May 15, 2017: Physical Chemistry Chemical Physics: PCCP
Ying Zhang, Wenfeng Sun, Xinke Wang, Jiasheng Ye, Shengfei Feng, Peng Han, Yan Zhang
A simple and energy-saving method has been proposed to actively modulate the spectra of terahertz (THz) waves radiated from two serial plasmas, which uses the background light to generate one plasma to make full use of the energy of the femtosecond laser. With this method, the modulation of the central frequency, spectral bandwidth, and spectral profile of the output THz waves have been observed. The shifting of the amplitude dip has been manipulated by changing the distance of the two serial plasmas. The manipulation results agree with the ones simulated by the transition-Cherenkov model...
May 15, 2017: Optics Letters
L Minkevičius, S Indrišiūnas, R Šniaukas, B Voisiat, V Janonis, V Tamošiūnas, I Kašalynas, G Račiukaitis, G Valušis
Multilevel phase Fresnel lenses (MPFLs) with a high numerical aperture for 0.58 THz frequencies were developed. The components based on a monocrystalline silicon wafer are prepared by patterning by a high-speed industrial-scale laser direct writing (LDW) system. Two consistent series of the terahertz-MPFLs with phase quantization levels varying between 2 and the continuous kinoform shape for the focal lengths of 5 and 10 mm were produced employing inherent flexibility of the LDW fabrication process. The focusing performance was studied at the optimal 0...
May 15, 2017: Optics Letters
Xu Chen, Wenhui Fan
A planar terahertz metamaterial consisting of square split ring resonators is proposed, and the excitation of toroidal dipolar resonance is demonstrated. Moreover, we theoretically investigate the strong interaction between graphene and toroidal dipolar resonance of the metamaterial. By varying its Fermi energy, the simulations show that graphene can actively modulate the transmission amplitude of toroidal dipolar resonance and even switch it off. The interaction of the toroidal dipolar resonance with monolayer graphene further highlights the ultrasensitive sensing characteristic of the planar metamaterial, which can be utilized for other graphene-like two-dimensional materials...
May 15, 2017: Optics Letters
V Dziom, A Shuvaev, A Pimenov, G V Astakhov, C Ames, K Bendias, J Böttcher, G Tkachov, E M Hankiewicz, C Brüne, H Buhmann, L W Molenkamp
The electrodynamics of topological insulators (TIs) is described by modified Maxwell's equations, which contain additional terms that couple an electric field to a magnetization and a magnetic field to a polarization of the medium, such that the coupling coefficient is quantized in odd multiples of α/4π per surface. Here we report on the observation of this so-called topological magnetoelectric effect. We use monochromatic terahertz (THz) spectroscopy of TI structures equipped with a semitransparent gate to selectively address surface states...
May 15, 2017: Nature Communications
M Kozina, T van Driel, M Chollet, T Sato, J M Glownia, S Wandel, M Radovic, U Staub, M C Hoffmann
We use ultrafast X-ray pulses to characterize the lattice response of SrTiO3 when driven by strong terahertz fields. We observe transient changes in the diffraction intensity with a delayed onset with respect to the driving field. Fourier analysis reveals two frequency components corresponding to the two lowest energy zone-center optical modes in SrTiO3. The lower frequency mode exhibits clear softening as the temperature is decreased while the higher frequency mode shows slight temperature dependence.
September 2017: Structural Dynamics (Melville, N.Y.)
Adam Dunkelberger, Ryan Compton, Paul A DeSario, Daniel Weidinger, Bryan T Spann, Irina R Pala, Christopher N Chervin, Debra R Rolison, Konrad Bussmann, Paul Cunningham, Joseph S Melinger, Brian G Alberding, Edwin J Heilweil, Jeffrey C Owrutsky
Solution-deposited nanoscale films of RuO2 ("nanoskins") are effective transparent conductors once calcined to 200 °C. Upon heating the nanoskins to higher temperature the nanoskins show increased transmission at 550 nm. Electronic microscopy and X-ray diffraction show that the changes in the optical spectrum are accompanied by the formation of rutile RuO2 nanoparticles. The mechanism for the spectral evolution is clearly observed with ultrafast optical measurements. Following excitation at 400 nm, nanoskins calcined at higher temperatures show increased transmission above 650 nm, consistent with the photobleaching of a surface-plasmon resonance (SPR) band...
June 2017: Plasmonics
Filchito Renee Bagsican, Andrew Winchester, Sujoy Ghosh, Xiang Zhang, Lulu Ma, Minjie Wang, Hironaru Murakami, Saikat Talapatra, Robert Vajtai, Pulickel M Ajayan, Junichiro Kono, Masayoshi Tonouchi, Iwao Kawayama
Adsorption of gas molecules on the surface of atomically layered two-dimensional (2D) materials, including graphene and transition metal dichalcogenides, can significantly affect their electrical and optical properties. Therefore, a microscopic and quantitative understanding of the mechanism and dynamics of molecular adsorption and desorption has to be achieved in order to advance device applications based on these materials. However, recent theoretical calculations have yielded contradictory results, particularly on the magnitude of the adsorption energy...
May 11, 2017: Scientific Reports
Xu Wu, Xiaodong Wu, Min Shao, Bin Yang
Here we investigated the structural changes of silk fibroin during Bombyx mori silkworm spinning and reconstitution process. X-ray diffraction, Fourier transform infrared spectroscopy, polarized optical microscopy, and terahertz (THz) spectroscopy were applied to monitor the structural features of silk fibroin from posterior, middle silk glands, to cocoons, and then to reconstituted silk. Results show that from silk gland to cocoon, fibroin experiences a significant transformation in crystal structure from a typical silk I, to a silk I-rich mixed structure, and finally to a typical silk II state, accompanied with a change in secondary structure from α-helix and random coil structures to preferential orientation β-sheets...
May 6, 2017: International Journal of Biological Macromolecules
K N Boldyrev, T N Stanislavchuk, A A Sirenko, D Kamenskyi, L N Bezmaternykh, M N Popova
We report on a new effect caused by the electron-phonon coupling in a stoichiometric rare-earth antiferromagnetic crystal subjected to an external magnetic field, namely, the appearance of a nonzero gap in the spectrum of electronic excitations in an arbitrarily small field. The effect was registered in the low-temperature far-infrared (terahertz) reflection spectra of an easy-axis antiferromagnet PrFe_{3}(BO_{3})_{4} in magnetic fields B_{ext}∥c. Both paramagnetic and magnetically ordered phases (including a spin-flop one) were studied in magnetic fields up to 30 T, and two bifurcation points were observed...
April 21, 2017: Physical Review Letters
Longqing Cong, Prakash Pitchappa, Chengkuo Lee, Ranjan Singh
Controlling the phase of local radiation by using exotic metasurfaces has enabled promising applications in a diversified set of electromagnetic wave manipulation such as anomalous wavefront deflection, flat lenses, and holograms. Here, we theoretically and experimentally demonstrate an active phase transition in a micro-electromechanical system-based metadevice where both the phase response and the dispersion of the metamaterial cavity are dynamically tailored. The phase transition is determined by the radiative and the absorptive losses in a metal-insulator-metal cavity that obeys the coupled-mode theory...
May 4, 2017: Advanced Materials
Christoph Deutsch, Martin Alexander Kainz, Michael Krall, Martin Brandstetter, Dominic Bachmann, Sebastian Schönhuber, Hermann Detz, Tobias Zederbauer, Donald MacFarland, Aaron Maxwell Andrews, Werner Schrenk, Mattias Beck, Keita Ohtani, Jérôme Faist, Gottfried Strasser, Karl Unterrainer
We report on high-power terahertz quantum cascade lasers based on low effective electron mass InGaAs/InAlAs semiconductor heterostructures with excellent reproducibility. Growth-related asymmetries in the form of interface roughness and dopant migration play a crucial role in this material system. These bias polarity dependent phenomena are studied using a nominally symmetric active region resulting in a preferential electron transport in the growth direction. A structure based on a three-well optical phonon depletion scheme was optimized for this bias direction...
April 19, 2017: ACS Photonics
Koijam Monika Devi, Amarendra K Sarma, Dibakar Roy Chowdhury, Gagan Kumar
We analyze plasmon induced transparency (PIT) in a planar terahertz metamaterial comprising of two C-shaped resonators and a cut-wire. The two C-shaped resonators are placed alternately on both sides of the cut-wire such that it exhibits a PIT effect when coupled with the cut wire. We have further shown that the PIT window is modulated by displacing the C-shaped resonators w.r.t. the cut-wire. A lumped element equivalent circuit model is reported to explain the numerical observations for different coupling configurations...
May 1, 2017: Optics Express
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