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Woongkyu Park, Youjin Lee, Taehee Kang, Jeeyoon Jeong, Dai-Sik Kim
Plasmon-mediated polymerization has been intensively studied for various applications including nanolithography, near-field mapping, and selective functionalization. However, these studies have been limited from the near-infrared to the ultraviolet regime. Here, we report a resist polymerization using intense terahertz pulses and various nanoantennas. The resist is polymerized near the nanoantennas, where giant field enhancement occurs. We experimentally show that the physical origin of the cross-linking is a terahertz electron emission from the nanoantenna, rather than multiphoton absorption...
May 17, 2018: Scientific Reports
Shuo Chen, Xiaoqiang Hua, Hongqiang Wang, Chenggao Luo, Yongqiang Cheng, Bin Deng
For synthetic aperture radars, it is difficult to achieve forward-looking and staring imaging with high resolution. Fortunately, terahertz coded-aperture imaging (TCAI), an advanced radar imaging technology, can solve this problem by producing various irradiation patterns with coded apertures. However, three-dimensional (3D) TCAI has two problems, including a heavy computational burden caused by a large-scale reference signal matrix, and poor resolving ability at low signal-to-noise ratios (SNRs). This paper proposes a 3D imaging method based on geometric measures (GMs), which can reduce the computational burden and achieve high-resolution imaging for low SNR targets...
May 16, 2018: Sensors
Jiayue Tong, Matthew C Conte, Thomas Goldstein, K Sigfrid Yngvesson, Joseph C Bardin, Jun Yan
Graphene, a single atomic layer of covalently bonded carbon atoms, has been investigated intensively for optoelectronics and represents a promising candidate for high-speed electronics. Here we present a microwave mixer constructed as an asymmetrically-contacted two-terminal graphene device based on the thermoelectric effect. We report a 50 GHz (minimum) mixer bandwidth as well as 130 V/W extrinsic direct-detection responsivity. Anomalous second-harmonic generation due to self-mixing in our graphene detector is also observed...
May 16, 2018: Nano Letters
Youwei Zhang, Hemei Zheng, Qiyuan Wang, Chunxiao Cong, Laigui Hu, Pengfei Tian, Ran Liu, Shi-Li Zhang, Zhi-Jun Qiu
Graphene is characterized by demonstrated unique properties for potential novel applications in photodetection operated in the frequency range from ultraviolet to terahertz. To date, detailed work on identifying the origin of photoresponse in graphene is still ongoing. Here, scanning photocurrent microscopy to explore the nature of photocurrent generated at the monolayer-multilayer graphene junction is employed. It is found that the contributing photocurrent mechanism relies on the mismatch of the Dirac points between the monolayer and multilayer graphene...
May 16, 2018: Small
Christian Nadell, Kebin Fan, Willie Padilla
Diffractive optics has long served as the basis of spectroscopic measurements of materials. Operation in the resonance domain further allows these elements to achieve high efficiency and polarization control. An effective grating theory is a practical tool for modeling such optics, and here we extend use of this theory to the terahertz region, experimentally demonstrating an all-dielectric binary off-axis diffractive lens. We achieve a high-efficiency, polarization-independent optic that both focuses and disperses terahertz light, suggesting potential applications in pharmaceutical, security, and semiconductor imaging...
May 15, 2018: Optics Letters
Rabi Chhantyal-Pun, Alexander Valavanis, James T Keeley, Pierluigi Rubino, Iman Kundu, Yingjun Han, Paul Dean, Lianhe Li, A Giles Davies, Edmund H Linfield
We demonstrate a gas spectroscopy technique, using self-mixing in a 3.4 terahertz quantum-cascade laser (QCL). All previous QCL spectroscopy techniques have required additional terahertz instrumentation (detectors, mixers, or spectrometers) for system pre-calibration or spectral analysis. By contrast, our system self-calibrates the laser frequency (i.e., with no external instrumentation) to a precision of 630 MHz (0.02%) by analyzing QCL voltage perturbations in response to optical feedback within a 0-800 mm round-trip delay line...
May 15, 2018: Optics Letters
Maya Mizuno, Noriko Yaekashiwa, Soichi Watanabe
The absorption characteristics of the dermis were reviewed in the terahertz range from 0.2 to 2 THz. The absorption magnitude of the dermis was higher than that of the epidermis model owing to the inclusion of collagen fibers. The heat denaturation of the collagen and the decrease of water content in the dermis caused a decrease in the absorption magnitude of the dermis. We verified that the absorption magnitude of collagen sheets at 1 THz similarly decreased by nearly 43% upon the heat treatment at approximately 70° C...
May 1, 2018: Biomedical Optics Express
Mariia Borovkova, Mikhail Khodzitsky, Petr Demchenko, Olga Cherkasova, Alexey Popov, Igor Meglinski
We apply terahertz time-domain spectroscopy for the quantitative non-invasive assessment of the water content in biological samples, such as Carpinus caroliniana tree leaves and pork muscles. The developed experimental terahertz time-domain spectroscopy system operates both in transmission and reflection modes. The Landau-Looyenga-Lifshitz-based model is used for the calculation of the water concentration within the samples. The results of the water concentration measurements are compared with the results of the gravimetric measurements...
May 1, 2018: Biomedical Optics Express
Yuan Jin, Liang Gao, Ji Chen, Chongzhao Wu, John L Reno, Sushil Kumar
The original PDF version of this Article contained an error in Equation 1. The 'Λ' was missing from the denominator. This has been corrected in the PDF version of the Article. The HTML version was correct from the time of publication.
May 14, 2018: Nature Communications
P D Hoang, G Andonian, I Gadjev, B Naranjo, Y Sakai, N Sudar, O Williams, M Fedurin, K Kusche, C Swinson, P Zhang, J B Rosenzweig
Photonic structures operating in the terahertz (THz) spectral region enable the essential characteristics of confinement, modal control, and electric field shielding for very high gradient accelerators based on wakefields in dielectrics. We report here an experimental investigation of THz wakefield modes in a three-dimensional photonic woodpile structure. Selective control in exciting or suppressing of wakefield modes with a nonzero transverse wave vector is demonstrated by using drive beams of varying transverse ellipticity...
April 20, 2018: Physical Review Letters
Andrea Tomadin, Sam M Hornett, Hai I Wang, Evgeny M Alexeev, Andrea Candini, Camilla Coletti, Dmitry Turchinovich, Mathias Kläui, Mischa Bonn, Frank H L Koppens, Euan Hendry, Marco Polini, Klaas-Jan Tielrooij
For many of the envisioned optoelectronic applications of graphene, it is crucial to understand the subpicosecond carrier dynamics immediately following photoexcitation and the effect of photoexcitation on the electrical conductivity-the photoconductivity. Whereas these topics have been studied using various ultrafast experiments and theoretical approaches, controversial and incomplete explanations concerning the sign of the photoconductivity, the occurrence and significance of the creation of additional electron-hole pairs, and, in particular, how the relevant processes depend on Fermi energy have been put forward...
May 2018: Science Advances
Rupali Rakshit, Santhosh Kumar Kadakuntla, Piyush Agarwal, Suman Sardar, Priyanka Saha, Kalyan Mandal, Dhanvir Singh Rana
Herein, we report the observation of unusual electronic and magnetic phases in traditional antiferromagnetic Co3O4 micromaterials and modulation of their properties on temperature scale. In particular, we demonstrate a comparative low energy carrier dynamics of Co3O4 micro-flower (MF) and micro-hollow flower (MHF) structures of same average size of 2 μm to unravel the ground state information induced by surface electronics across the insulator-semiconductor transition using terahertz (THz) time domain spectroscopy...
May 11, 2018: ACS Applied Materials & Interfaces
Zenghui Xu, Dong Wu, Yumin Liu, Chang Liu, Zhongyuan Yu, Li Yu, Han Ye
We propose and numerically demonstrate an ultra-broadband graphene-based metamaterial absorber, which consists of multi-layer graphene/dielectric on the SiO2 layer supported by a metal substrate. The simulated result shows that the proposed absorber can achieve a near-perfect absorption above 90% with a bandwidth of 4.8 Thz. Owing to the flexible tunability of graphene sheet, the state of the absorber can be switched from on (absorption > 90%) to off (reflection > 90%) in the frequencies range of 3-7...
May 9, 2018: Nanoscale Research Letters
Amit Agarwal, Miriam S Vitiello, Leonardo Viti, Anna Cupolillo, Antonio Politano
Herein, we explore the main features and the prospect of plasmonics with two-dimensional semiconductors. Plasmonic modes in each class of van der Waals semiconductors have their own peculiarities, along with potential technological capabilities. Plasmons of transition-metal dichalcogenides share features typical of graphene, due to their honeycomb structure, but with damping processes dominated by intraband rather than interband transitions, unlike graphene. Spin-orbit coupling strongly affects the plasmonic spectrum of buckled honeycomb lattices (silicene and germanene), while the anisotropic lattice of phosphorene determines different propagation of plasmons along the armchair and zigzag directions...
May 9, 2018: Nanoscale
Qin Xie, Guangxi Dong, Ben-Xin Wang, Wei-Qing Huang
Quad-band terahertz absorber with single-sized metamaterial design formed by a perforated rectangular resonator on a gold substrate with a dielectric gap in between is investigated. The designed metamaterial structure enables four absorption peaks, of which the first three peaks have large absorption coefficient while the last peak possesses a high Q (quality factor) value of 98.33. The underlying physical mechanisms of these peaks are explored; it is found that their near-field distributions are different...
May 8, 2018: Nanoscale Research Letters
Kamil Olejník, Tom Seifert, Zdeněk Kašpar, Vít Novák, Peter Wadley, Richard P Campion, Manuel Baumgartner, Pietro Gambardella, Petr Němec, Joerg Wunderlich, Jairo Sinova, Petr Kužel, Melanie Müller, Tobias Kampfrath, Tomas Jungwirth
The speed of writing of state-of-the-art ferromagnetic memories is physically limited by an intrinsic gigahertz threshold. Recently, realization of memory devices based on antiferromagnets, in which spin directions periodically alternate from one atomic lattice site to the next has moved research in an alternative direction. We experimentally demonstrate at room temperature that the speed of reversible electrical writing in a memory device can be scaled up to terahertz using an antiferromagnet. A current-induced spin-torque mechanism is responsible for the switching in our memory devices throughout the 12-order-of-magnitude range of writing speeds from hertz to terahertz...
March 2018: Science Advances
Ashish Chanana, Xiaojie Liu, Chuang Zhang, Zeev Valy Vardeny, Ajay Nahata
The ability to control the response of metamaterial structures can facilitate the development of new terahertz devices, with applications in spectroscopy and communications. We demonstrate ultrafast frequency-agile terahertz metamaterial devices that enable such a capability, in which multiple perovskites can be patterned in each unit cell with micrometer-scale precision. To accomplish this, we developed a fabrication technique that shields already deposited perovskites from organic solvents, allowing for multiple perovskites to be patterned in close proximity...
May 2018: Science Advances
Hiroyuki Katsuki, Nobuyuki Takei, Christian Sommer, Kenji Ohmori
Coherent control is a technique to manipulate wave functions of matter with light. Coherent control of isolated atoms and molecules in the gas phase is well-understood and developed since the 1990s, whereas its application to condensed matter is more difficult because its coherence lifetime is shorter. We have recently applied this technique to condensed matter samples, one of which is solid para-hydrogen ( p-H2 ). Intramolecular vibrational excitation of solid p-H2 gives an excited vibrational wave function called a "vibron", which is delocalized over many hydrogen molecules in a manner similar to a Frenkel exciton...
May 7, 2018: Accounts of Chemical Research
Z V Gagkaeva, E S Zhukova, V Grinenko, A K Grebenko, K V Sidoruk, T A Voeikova, M Dressel, B P Gorshunov
Employing optical spectroscopy we have performed a comparative study of the dielectric response of extracellular matrix and filaments of electrogenic bacteria Shewanella oneidensis MR-1, cytochrome c, and bovine serum albumin. Combining infrared transmission measurements on thin layers with data of the terahertz spectra, we obtain the dielectric permittivity and AC conductivity spectra of the materials in a broad frequency band from a few cm-1 up to 7000 cm-1 in the temperature range from 5 to 300 K. Strong absorption bands are observed in the three materials that cover the range from 10 to 300 cm-1 and mainly determine the terahertz absorption...
May 7, 2018: Journal of Biological Physics
Mohammad Faisal, Md Shariful Islam
A suspended core microstructured fiber with extremely high birefringence has been proposed for terahertz (THz) wave propagation. An elliptical-shaped core has been formed with slotted rectangular airholes to disrupt the vertical symmetry of the refractive index of the designed fiber. Different design parameters such as the core diameter, ellipticity, porosity, and suspended strut width have been checked to achieve optimum performance from the fiber. The resultant birefringence of the proposed fiber is unprecedented, of the order of 10-1 (1...
May 1, 2018: Applied Optics
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