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Y-J Chen, Kh Zakeri, A Ernst, H J Qin, Y Meng, J Kirschner
Quantum confinement permits the existence of multiple terahertz magnon modes in atomically engineered ultrathin magnetic films and multilayers. By means of spin-polarized high-resolution electron energy-loss spectroscopy, we report on the direct experimental detection of all exchange-dominated terahertz confined magnon modes in a 3 ML Co film. We demonstrate that, by tuning the structural and magnetic properties of the Co film, through its epitaxial growth on different surfaces, e.g., Ir(001), Cu(001), and Pt(111), one can achieve entirely different in-plane magnon dispersions, characterized by positive and negative group velocities...
December 29, 2017: Physical Review Letters
Andriy E Serebryannikov, Kamil B Alici, Ekmel Ozbay, Akhlesh Lakhtakia
Temperature-sensitive scattering of terahertz (THz) waves by infinitely long, cylindrical core-shell structures was theoretically studied. Each structure is a dielectric cylinder coated with an InSb shell illuminated by either a transverse-electric (TE) or a transverse-magnetic (TM) plane wave. InSb is a thermally tunable semiconductor showing a transition from dielectric to plasmonic state at THz frequencies. Accordingly, the total scattering efficiency (TSE) can be thermally tuned for both polarization states of the incident plane wave...
January 8, 2018: Optics Express
Shuiqin Zheng, Xinjian Pan, Yi Cai, Qinggang Lin, Ying Li, Shixiang Xu, Jingzhen Li, Dianyuan Fan
This publisher's note corrects an error in one of the authors' names and an error in one of the grant numbers in Opt. Lett.42, 4263 (2017).
January 15, 2018: Optics Letters
T C H Liew, A V Kavokin
Bosonic cascade lasers are terahertz (THz) lasers based on stimulated radiative transitions between bosonic condensates of excitons or exciton-polaritons confined in a trap. We study the interaction of an incoming THz pulse resonant in frequency with the transitions between neighboring energy levels of the cascade. We show that at certain optical pump conditions the cascade becomes transparent to the incident pulse: it neither absorbs nor amplifies it in the mean-field approximation. The populations of intermediate levels of the bosonic cascade change as the THz pulse passes, nevertheless...
January 15, 2018: Optics Letters
Fangrong Hu, Yixing Fan, Xiaowen Zhang, Wenying Jiang, Yuanzhi Chen, Peng Li, Xianhua Yin, Wentao Zhang
We experimentally demonstrated a tunable terahertz bandpass filter based on microelectromechanical systems (MEMS) reconfigurable metamaterials. The unit cell of the filter consists of two split-ring resonators (SRRs) and a movable bar. Initially, the movable bar situates at the center of the unit cell, and the filter has two passbands whose central frequencies locate at 0.65 and 0.96 THz. The intensity of the two passbands can be actively modulated by the movable bar, and a maximum modulation depth of 96% is achieved at 0...
January 1, 2018: Optics Letters
Xiaolu Li, Ya Bai, Na Li, Peng Liu
We generate terahertz radiation in a supersonic jet of nitrogen molecules pumped by intense two-color laser pulses. The tuning of terahertz spectra from blue shift to red shift is observed by increasing laser power and stagnation pressure, and the red shift range is enlarged with the increased stagnation pressure. Our simulation reveals that the plasma absorption of the oscillation currents and expanded plasma column owing to increased laser intensity and gas number density are crucial factors in the recurrence of the red shift of terahertz spectra...
January 1, 2018: Optics Letters
O Kosareva, M Esaulkov, N Panov, V Andreeva, D Shipilo, P Solyankin, A Demircan, I Babushkin, V Makarov, U Morgner, A Shkurinov, A Savel'ev
We individually control polarizations of 800 and 400 nm beams, which form a two-color femtosecond plasma filament in air irradiating a linear-to-elliptical THz signal. We detected a threshold-like appearance of THz ellipticity at the angle of ∼85° between the fundamental and second-harmonic field polarization directions. The simulations confirm the abrupt change of THz polarization and reveal that the weak ellipticity of the second harmonic is sufficient to generate essentially elliptical THz radiation.
January 1, 2018: Optics Letters
Francesco Chiadini, Akhlesh Lakhtakia
Transmission of a normally incident plane wave through a metasurface with bicontrollable subwavelength scattering elements was simulated using a commercial software. Some pixels composing the H-shaped scattering elements were made of a magnetostatically controllable material whereas the remaining pixels were made of a thermally controllable material, the metasurface designed to operate in the terahertz spectral regime. The copolarized transmission coefficients were found to exhibit stopbands that shift when either a magnetostatic field is applied or the temperature is increased or both...
January 10, 2018: Applied Optics
Zhifang Feng, Jie Lin, Shuai Feng
The transmission properties of an off-planar integrated circuit including two wavelength division demultiplexers are designed, simulated, and analyzed in detail by the finite-difference time-domain method. The results show that the wavelength selection for different ports (0.404[c/a] at B2 port, 0.389[c/a] at B3 port, and 0.394[c/a] at B4 port) can be realized by adjusting the parameters. It is especially important that the off-planar integration between two complex devices is also realized. These simulated results give valuable promotions in the all-optical integrated circuit, especially in compact integration...
January 10, 2018: Applied Optics
Dan Li, Chunya Luo, Yebin Xu, Jing Zhang, Liang Wu, Huaixing Wang, Songjie Shi, Furi Ling, Jianquan Yao
The dielectric properties of 0.6CaTiO3-0.4NdAlO3 ceramics under external optical fields were investigated by terahertz time-domain spectroscopy in a frequency range of 0.2 THz to 1 THz at room temperature. It could be found that the variation of the real part of complex permittivity is approximately 0.31 in the frequency range of 0.2 THz to 1 THz. However the imaginary part of the dielectric constant does not change appreciably with the external optical field. The micromechanism of these results was attributed to the built-in electric field caused by the excited free carriers in the ceramics...
January 1, 2018: Applied Optics
Daniel L Marks, David R Smith
The radiating mode of a cavity antenna at a particular frequency is fixed. However, by actively modulating the permittivity inside the cavity, the radiating mode may be changed. Using time-independent perturbation theory, we derive the modes of a cavity perturbed by many modulating elements. It is found that with a sufficient number of modulators of sufficient strength, the number of unique fields radiated by the cavity may reach a limit determined by the number of unperturbed cavity modes. The number of addressable radiated fields increases exponentially with the number of modulators; however, perturbations involving the interaction of several modulators become progressively weaker...
January 1, 2018: Journal of the Optical Society of America. A, Optics, Image Science, and Vision
Wen Xiang Lim, Manukumara Manjappa, Yogesh Kumar Srivastava, Longqing Cong, Abhishek Kumar, Kevin F MacDonald, Ranjan Singh
Incorporating semiconductors as active media into metamaterials offers opportunities for a wide range of dynamically switchable/tunable, technologically relevant optical functionalities enabled by strong, resonant light-matter interactions within the semiconductor. Here, a germanium-thin-film-based flexible metaphotonic device for ultrafast optical switching of terahertz radiation is experimentally demonstrated. A resonant transmission modulation depth of 90% is achieved, with an ultrafast full recovery time of 17 ps...
January 12, 2018: Advanced Materials
Shengxiang Wang, Lei Kang, Douglas H Werner
Compared with natural materials, chiral metamaterials have been demonstrated with orders of magnitude stronger chiroptical response, which provides the basis for applications such as ultracompact polarization components and plasmonic-enhanced biosensing. Terahertz chiral metamaterials that allow dynamic polarization control of terahertz waves are of great practical interest, but remain extremely rare. Here, we show that hybrid metamaterials integrated with vanadium dioxide (VO2) exhibiting phase transition can enable dynamically tunable chiroptical responses at terahertz frequencies...
January 9, 2018: Scientific Reports
Kyu Been Kwon, Teyoun Kang, Hyung Seon Song, Young-Kuk Kim, Bernhard Ersfeld, Dino A Jaroszynski, Min Sup Hur
Emission of radiation from electrons undergoing plasma oscillations (POs) at the plasma frequency has attracted interest because of the existence of intriguing and non-trivial coupling mechanism between the electrostatic PO and the emitted electromagnetic wave. While broadband emission from plasma waves in inhomogeneous plasma is well known, the underlying physics of narrowband emission at the plasma frequency observed in experiments and in solar radio-bursts is obscure. Here we show that a spatially-localized plasma dipole oscillation (PDO) can be generated when electrons are trapped in a moving train of potential wells produced by the ponderomotive force of two slightly detuned laser pulses that collide in plasma and give rise to a burst of quasi-monochromatic radiation...
January 9, 2018: Scientific Reports
Mikhail Morozov, Ilya Moiseenko, Vyacheslav Popov
Amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. Plasmon wave in symmetric double-layer graphene structure splits into two branches with a symmetric and an antisymmetric distribution of tangential to graphene component of the electric field across the plane of symmetry of the structure. It is shown that normalized to the wavelength terahertz plasmon amplification factor of the symmetric mode in the double-layer graphene structure could be greater than that in a single graphene layer by 4 orders of magnitude...
January 9, 2018: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Alberto Carpinteri, Gianfranco Piana, Andrea Bassani, Giuseppe Lacidogna
Mechanical vibration in the Terahertz range is believed to be connected with protein functions. In this paper, we present the results of a normal-mode analysis (modal analysis) of a Na/K-ATPase all-atom model, focusing the attention on low-frequency vibration modes. The numerical model helps in the interpretation of experimental results previously obtained by the authors via Raman spectroscopy of Na/K-ATPase samples, where several unassigned peaks were found in the sub-500 cm-1 range. In particular, vibration modes corresponding to peaks at 27, 190, and 300 cm-1, found experimentally, are confirmed here numerically, together with some other modes at lower frequencies (wavenumbers) that were not possible to observe in the experimental test...
January 8, 2018: Journal of Biomolecular Structure & Dynamics
Srabani Kar, Van Luan Nguyen, Dipti R Mohapatra, Young Hee Lee, A K Sood
Photoinduced terahertz conductivity Δσ(ω) of Bernal stacked bilayer graphene (BLG) with different dopings is measured by time resolved optical pump terahertz probe spectroscopy. The real part of photoconductivity Δσ(ω) (ΔσRe(ω)) is positive throughout the spectral range 0.5-2.5 THz in low doped BLG. This is in sharp contrast to Δσ(ω) for high doped bilayer graphene where ΔσRe(ω) is negative on low frequency and positive on the high frequency side. We use Boltzmann transport theory to understand quantitatively the frequency dependence of Δσ(ω), demanding the energy dependence of different scattering rates such as short-range impurity scattering, Coulomb scattering, carrier-acoustic phonon scattering, and substrate surface optical phonon scattering...
January 8, 2018: ACS Nano
Ching-Chung Hsueh, Reuven Gordon, Joerg Rottler
We use molecular simulations to demonstrate the formation of a vacuum layer around a vibrating nanoparticle in a liquid. This vacuum layer forms readily for high frequencies with respect to the Einstein frequency of the fluid, even with small amplitude vibrations. The opposite is true for low frequencies, where large amplitudes are required to demonstrate the vacuum layer. With the vacuum layer forming, the quality factor of the oscillations increases substantially. The findings provide an interpretation of our recent experiments that show the onset of high-quality resonances of nanoparticles in water [Xiang et al...
January 8, 2018: Nano Letters
Jianjun Liu, Jianquan Kan
In this paper, based on the terahertz spectrum, a new identification method of genetically modified material by support vector machine (SVM) based on affinity propagation clustering is proposed. This algorithm mainly uses affinity propagation clustering algorithm to make cluster analysis and labeling on unlabeled training samples, and in the iterative process, the existing SVM training data are continuously updated, when establishing the identification model, it does not need to manually label the training samples, thus, the error caused by the human labeled samples is reduced, and the identification accuracy of the model is greatly improved...
January 3, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
Hiroyuki Yoshino, Yuko Hara, Masafumi Dohi, Kazunari Yamashita, Tadashi Hakomori, Shin-Ichiro Kimura, Yasunori Iwao, Shigeru Itai
Scale-up approaches for film coating process have been established for each type of film coating equipment from thermodynamic and mechanical analyses for several decades. The objective of the present study was to establish a versatile scale-up approach for film coating process applicable to commercial production that is based on critical quality attribute (CQA) using the Quality by Design (QbD) approach and is independent of the equipment used. Experiments on a pilot scale using the Design of Experiment (DoE) approach were performed to find a suitable CQA from surface roughness, contact angle, color difference, and coating film properties by terahertz spectroscopy...
January 5, 2018: AAPS PharmSciTech
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