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Yong Du, Qiang Cai, Jiadan Xue, Qi Zhang, Dan Qin
The vibrational spectra of 5-fluorocytosine, fumaric acid and their cocrystal were measured using terahertz time-domain spectroscopy (THz-TDS) and Raman spectroscopy at room temperature. Experimental THz results show that the cocrystal has distinct fingerprint spectra in terahertz region. The absorption peaks observed in the terahertz spectra of the cocrystal were at 0.61 and 0.91THz. These are quite different from corresponding raw starting materials. Raman spectra also show similar results about differences between the cocrystal and corresponding raw starting materials...
February 7, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
C Evain, E Roussel, M Le Parquier, C Szwaj, M-A Tordeux, J-B Brubach, L Manceron, P Roy, S Bielawski
In recent synchrotron radiation facilities, the use of short (picosecond) electron bunches is a powerful method for producing giant pulses of terahertz coherent synchrotron radiation. Here we report on the first direct observation of these pulse shapes with a few picoseconds resolution, and of their dynamics over a long time. We thus confirm in a very direct way the theories predicting an interplay between two physical processes. Below a critical bunch charge, we observe a train of identical THz pulses (a broadband Terahertz comb) stemming from the shortness of the electron bunches...
February 3, 2017: Physical Review Letters
Jeong Min Woo, Sajid Hussain, Jae-Hyung Jang
A terahertz (THz) in-line polarization converter that yields a polarization conversion ratio as high as 99.9% is demonstrated at 1 THz. It has double-layer slot structures oriented in orthogonal directions that are electrically connected by 1/8-wavelngth-long through-via holes beside the slot structures. The slots on the front metal-plane respond to the incident THz wave with polarization orthogonal to the slots and generates a circulating surface current around the slots. The surface current propagates along a pair of through-via holes that function as a two-wire transmission line...
February 17, 2017: Scientific Reports
H B Zhuo, S J Zhang, X H Li, H Y Zhou, X Z Li, D B Zou, M Y Yu, H C Wu, Z M Sheng, C T Zhou
Generation of intense coherent THz radiation by obliquely incidenting an intense laser pulse on a wire target is studied using particle-in-cell simulation. The laser-accelerated fast electrons are confined and guided along the surface of the wire, which then acts like a current-carrying line antenna and under appropriate conditions can emit electromagnetic radiation in the THz regime. For a driving laser intensity ∼3×10^{18}W/cm^{2} and pulse duration ∼10 fs, a transient current above 10 KA is produced on the wire surface...
January 2017: Physical Review. E
Nezih Tolga Yardimci, Mona Jarrahi
Plasmonic photoconductive antennas have great promise for increasing responsivity and detection sensitivity of conventional photoconductive detectors in time-domain terahertz imaging and spectroscopy systems. However, operation bandwidth of previously demonstrated plasmonic photoconductive antennas has been limited by bandwidth constraints of their antennas and photoconductor parasitics. Here, we present a powerful technique for realizing broadband terahertz detectors through large-area plasmonic photoconductive nano-antenna arrays...
February 16, 2017: Scientific Reports
Hong-Wei Wu, Hua-Jun Chen, Hui-Ying Fan, Yang Li, Xian-Wen Fang
We demonstrate that a defect unit in periodic textured closed surfaces is able to trap spoof surface plasmons (SPs) into a deep subwavelength scale. The resonant frequency of a trapped spoof SP can be tuned freely by properly tailoring the dimension of the defect unit. By introducing multiple defect units with different dimensions at different positions of the textured closed surfaces, the spoof SPs with different frequencies trapped effectively at desired places are also demonstrated. In addition, we further design a graded defect structure with continuously variable dimensions to trap the spoof SPs over an ultrawide spectral band...
February 15, 2017: Optics Letters
Natsuki Kanda, Kuniaki Konishi, Natsuki Nemoto, Katsumi Midorikawa, Makoto Kuwata-Gonokami
Terahertz (THz) imaging has a strong potential for applications because many molecules have fingerprint spectra in this frequency region. Spectroscopic imaging in the THz region is a promising technique to fully exploit this characteristic. However, the performance of conventional techniques is restricted by the requirement of multidimensional scanning, which implies an image data acquisition time of several minutes. In this study, we propose and demonstrate a novel broadband THz spectroscopic imaging method that enables real-time image acquisition using a high-sensitivity THz camera...
February 15, 2017: Scientific Reports
Guoqing Hu, Tatsuya Mizuguchi, Xin Zhao, Takeo Minamikawa, Takahiko Mizuno, Yuli Yang, Cui Li, Ming Bai, Zheng Zheng, Takeshi Yasui
A single, free-running, dual-wavelength mode-locked, erbium-doped fibre laser was exploited to measure the absolute frequency of continuous-wave terahertz (CW-THz) radiation in real time using dual THz combs of photo-carriers (dual PC-THz combs). Two independent mode-locked laser beams with different wavelengths and different repetition frequencies were generated from this laser and were used to generate dual PC-THz combs having different frequency spacings in photoconductive antennae. Based on the dual PC-THz combs, the absolute frequency of CW-THz radiation was determined with a relative precision of 1...
February 10, 2017: Scientific Reports
Sesha Bamini N, Hynek Němec, Karel Žídek, Mohamed Abdellah, Mohammed J Al-Marri, Pavel Chábera, Carlito Ponseca, Kaibo Zheng, Tönu Pullerits
Photoinitiated charge carrier dynamics in ZnO nanoparticles sensitized by CdSe quantum dots is studied using transient absorption spectroscopy and time-resolved terahertz spectroscopy. The evolution of the transient spectra shows that electron injection occurs in a two-step process, where the formation of a charge transfer state (occurring in several picoseconds) is followed by its dissociation within tens of picoseconds. The photoconductivity of electrons injected into the ZnO nanoparticles is lower than that of charges photogenerated directly in ZnO...
February 9, 2017: Physical Chemistry Chemical Physics: PCCP
Fan Zhang, Kaijun Song, Yong Fan
A two-dimensional (2D) diffraction model for the calculation of the diffraction field in 2D space and its applications to terahertz parallel-plate waveguide power splitters are proposed in this paper. Compared with the Huygens-Fresnel principle in three-dimensional (3D) space, the proposed model provides an approximate analytical expression to calculate the diffraction field in 2D space. The diffraction filed is regarded as the superposition integral in 2D space. The calculated results obtained from the proposed diffraction model agree well with the ones by software HFSS based on the element method (FEM)...
February 9, 2017: Scientific Reports
G G Hernandez-Cardoso, S C Rojas-Landeros, M Alfaro-Gomez, A I Hernandez-Serrano, I Salas-Gutierrez, E Lemus-Bedolla, A R Castillo-Guzman, H L Lopez-Lemus, E Castro-Camus
Most people with diabetes suffer some deterioration of the feet. Diabetic foot syndrome causes ulceration in about 15% of cases and such deterioration leads to amputation in about 2.5% of diabetic patients, diminishing their quality of life and generating extraordinary costs for patients and public health systems. Currently, there is no objective method for the detection of diabetic foot syndrome in its early stages. We propose terahertz imaging as a method for the evaluation of such deterioration. This screening method could aid the prevention and medical treatment of this condition in the future...
February 6, 2017: Scientific Reports
Jianyuan Qin, Lijuan Xie, Yibin Ying
Despite numerous methods for the detection of antibiotic residues, they are usually destructive and require tedious pre-treatment. Terahertz time-domain spectroscopy (THz-TDS) is an emerging technology that has advantages for analyzing chemical and biological compounds since THz waves are very sensitive to the molecular vibrational modes. Here we incorporated attenuated total reflection technique into the THz-TDS and demonstrated that this technology (ATR THz-TDS) allowed to determine the complex refractive indices of tetracycline hydrochloride (TCH) solutions with high accuracy and could be used to predict their concentrations...
June 1, 2017: Food Chemistry
Md Saiful Islam, Jakeya Sultana, Javid Atai, Derek Abbott, Sohel Rana, Mohammad Rakibul Islam
In this paper, we present the design and analysis of a novel hybrid porous core octagonal lattice photonic crystal fiber for terahertz (THz) wave guidance. The numerical analysis is performed using a full-vector finite element method (FEM) that shows that 80% of bulk absorption material loss of cyclic olefin copolymer (COC), commercially known as TOPAS can be reduced at a core diameter of 350 μm. The obtained effective material loss (EML) is as low as 0.04  cm<sup>-1</sup> at an operating frequency of 1 THz with a core porosity of 81%...
February 1, 2017: Applied Optics
Debanjan Polley, Animesh Patra, Anjan Barman, Rajib Kumar Mitra
We report the controllable conductivity of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes with their surface walls decorated by gold nanoparticles (Au NPs) with varying concentration in terahertz (THz) frequency range. Colloidal Au NPs of nominal diameter ∼15  nm are synthesized by the reduction of gold chloride solution using tri-sodium citrate. A simple chemical route is followed to attach Au NPs on the surfaces of both types of carbon nanotubes (CNTs). The attachment of Au NPs on the sidewalls of CNTs is confirmed by UV-visible spectroscopy and scanning electron microscope images...
February 1, 2017: Applied Optics
Yan Liu, Yibo Wang, Genquan Han, Yao Shao, Cizhe Fang, Siqing Zhang, Yan Huang, Jincheng Zhang, Yue Hao
In this paper, we propose an ultrathin THz plasmonic metallic strip based on graded grating structure with thermo-optic material, which exhibits a strong engineering of trapping and releasing electromagnetic waves in terahertz regimes. The dispersion properties of the ultrathin spoof slow-wave plasmonic graded grating waveguide are characterized using the finite element method, and the propagation characteristics of the grating structures are thoroughly analyzed by the dispersion curves, electric field magnitude distribution, and electric field vertical distribution...
January 23, 2017: Optics Express
Jie Zhao, Qiang Cheng, Tian Qi Wang, Wei Yuan, Tie Jun Cui
A method for fast design of broadband terahertz diffusion metasurface is presented. The proposed metasurface is composed by three kinds of simply patterned elements with different resonant properties. To obtain the best broadband performance with the lowest backward reflections, a genetic algorithm is developed to manipulate the resonances for the fast determination of element geometries. An inverse discrete Fourier transform method is used to predict the scattering pattern of the metasurface with high accuracy and low time consumption, significantly enhancing the efficiency of the array-pattern design...
January 23, 2017: Optics Express
Longfang Ye, Yifan Xiao, Na Liu, Zhengyong Song, Wei Zhang, Qing Huo Liu
We proposed a novel planar terahertz (THz) plasmonic waveguide with folded stub arrays to achieve excellent terahertz propagation performance with tight field confinement and compact size based on the concept of spoof surface plasmon polaritons (spoof SPPs). It is found that the waveguide propagation characteristics can be directly manipulated by increasing the length of the folded stubs without increasing its lateral dimension, which exhibits much lower asymptotic frequency of the dispersion relation and even tighter terahertz field confinement than conventional plasmonic waveguides with rectangular stub arrays...
January 23, 2017: Optics Express
Steven R Murrill, Charmaine C Franck, Eddie L Jacobs, Douglas T Petkie, Frank C De Lucia
The U.S. Army Research Laboratory has continued to develop and enhance a millimeter-wave (MMW) and submillimeter-wave (SMMW)/terahertz (THz)-band imaging system performance prediction and analysis tool for both the detection and identification of concealed weaponry and for pilotage obstacle avoidance. The details of the MATLAB-based model that accounts for the effects of all critical sensor and display components, for the effects of atmospheric attenuation, concealment material attenuation, active illumination, target and background orientation, target and background thermal emission, and various imaging system architectures have been reported on in 2005, 2007, and 2011...
January 20, 2017: Applied Optics
Yue-Yu Xiao, Shao-Fan Lu
A terahertz (THz) fiber circular polarizer based on suspended core fibers is proposed and analyzed. The THz mode guides within a subwavelength-scale core, which is suspended in a polymer tube. The dry air inner cladding not only suppresses the absorption loss of the device but also supports the leaky cladding modes. The circularly polarized core mode with the same handedness of the grating couples to the leaky cladding modes suffers from loss near resonant frequencies due to the spiral structure of the fiber...
January 20, 2017: Applied Optics
Tingting Pan, Shaoping Li, Tao Zou, Zheng Yu, Bo Zhang, Chenyang Wang, Jianbing Zhang, Mingxia He, Hongwei Zhao
The low-frequency vibrational property of l-phenylalanine (l-Phe) and l-phenylalanine monohydrate (l-Phe·H2O) has been investigated by terahertz time-domain spectroscopy (THz-TDS) at room and low temperature ranging from 0.5 to 4.5THz. Distinctive THz absorption spectra of the two compounds were observed. Density functional theory (DFT) calculations based on the crystal structures have been performed to simulate the vibrational modes of l-Phe and l-Phe·H2O and the results agree well with the experimental observations...
January 26, 2017: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
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