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Jianglou Huang, Jinsong Liu, Kejia Wang, Zhengang Yang, Xiaming Liu
By means of factor analysis approach, a method of molecule classification is built based on the measured terahertz absorption spectra of the molecules. A data matrix can be obtained by sampling the absorption spectra at different frequency points. The data matrix is then decomposed into the product of two matrices: a weight matrix and a characteristic matrix. By using the K-means clustering to deal with the weight matrix, these molecules can be classified. A group of samples (spirobenzopyran, indole, styrene derivatives and inorganic salts) has been prepared, and measured via a terahertz time-domain spectrometer...
March 9, 2018: Spectrochimica Acta. Part A, Molecular and Biomolecular Spectroscopy
E Curry, S Fabbri, J Maxson, P Musumeci, A Gover
Terahertz (THz) radiation promises breakthrough advances in compact advanced accelerators due to the gigavolts-per-meter fields achievable, but the challenge of maintaining overlap and synchronism between beams and short laser-generated THz pulses has so far limited interactions to the few-millimeter scale. We implement a novel scheme for simultaneous group and phase velocity matching of nearly single-cycle THz radiation with a relativistic electron beam for meter-scale inverse free-electron laser interaction in a magnetic undulator, resulting in energy modulations of up to 150 keV using modest THz pulse energies (≤1  μJ)...
March 2, 2018: Physical Review Letters
Changlong Liu, Lin Wang, Xiaoshuang Chen, Jing Zhou, Weiwei Tang, Wanlong Guo, Jin Wang, Wei Lu
The present work reports on a graphene-like material that is promising for photodetection applications due to its high optical absorption and layer-dependent properties. To date, only narrowband photodetectors have been realized; therefore, extending the working wavelength is becoming more imperative for applications such as high-contrast imaging and remote sensing. In this work, we developed a novel detection technique that provides enhanced performance across the infrared and terahertz bands by using an antenna-assisted top-gated black phosphorus phototransistor...
March 16, 2018: Nanoscale
Sreetama Pal, Nirnay Samanta, Debasish Das Mahanta, Rajib Kumar Mitra, Amitabha Chattopadhyay
Biological membranes are highly organized supramolecular assemblies of lipids and proteins. The membrane interface separates the outer (bulk) aqueous phase from the hydrophobic membrane interior. In this work, we have explored the microstructure and collective dynamics of the membrane interfacial hydration shell in zwitterionic and negatively charged phospholipid membrane bilayers using terahertz time-domain spectroscopy. We show here that the relaxation time constants of water hydrogen bond network exhibit a unique "rise and dip" pattern with increasing lipid concentration...
March 15, 2018: Journal of Physical Chemistry. B
Coleen T Nemes, John R Swierk, Charles A Schmuttenmaer
Terahertz spectroscopy is broadly applicable for the study of a wide variety of materials, but spectroelectrochemistry has not been performed in the THz range due to the lack of a THz-transparent electrochemical cell. While THz-transparent electrodes do exist, they had never been utilized in a complete three-electrode cell, which is the configuration required for accurate potential control in aqueous media. We have designed and constructed a THz-transparent three-electrode elec-trochemical cell and have performed THz spectroelectrochemistry of a SnO2 thin film...
March 15, 2018: Analytical Chemistry
Michael Kolano, Benedict Gräf, Stefan Weber, Daniel Molter, Georg von Freymann
We demonstrate a polarization-multiplexed, single-laser system for terahertz (THz) time-domain spectroscopy without an external delay line. The fiber laser emits two pulse trains with independently adjustable repetition rates, utilizing only one laser-active section and one pump diode. With a standard fiber-coupled THz setup and a polarization-multiplexed optical amplifier, we are able to measure transients with a spectral bandwidth of 1.5 THz and a dynamic range of 50 dB in a measurement time of 1 s. Based on the novel laser architecture, we call this new approach single-laser polarization-controlled optical sampling, or SLAPCOPS...
March 15, 2018: Optics Letters
M B Agranat, O V Chefonov, A V Ovchinnikov, S I Ashitkov, V E Fortov, P S Kondratenko
We report on the experimental observation of high-power terahertz-radiation-induced damage in a thin aluminum film with a thickness less than a terahertz skin depth. Damage in a thin metal film produced by a single terahertz pulse is observed for the first time. The damage mechanism induced by a single terahertz pulse could be attributed to thermal expansion of the film causing debonding of the film from the substrate, film cracking, and ablation. The damage pattern induced by multiple terahertz pulses at fluences below the damage threshold is quite different from that observed in single-pulse experiments...
February 23, 2018: Physical Review Letters
Changcheng Shi, Yuting Ma, Jin Zhang, Dongshan Wei, Huabin Wang, Xiaoyu Peng, Mingjie Tang, Shihan Yan, Guokun Zuo, Chunlei Du, Hongliang Cui
Chondroitin sulfate (CS), derived from cartilage tissues, is an important type of biomacromolecule. In this paper, the terahertz time-domain spectroscopy (THz-TDS) was investigated as a potential method for content detection of CS. With the increase of the CS content, the THz absorption coefficients of the CS/polyethylene mixed samples linearly increase. The refractive indices of the mixed samples also increase when the CS content increases. The extinction coefficient of CS demonstrates the THz frequency dependence to be approximately the power of 1...
March 1, 2018: Biomedical Optics Express
Bao C Q Truong, Anthony J Fitzgerald, Shuting Fan, Vincent P Wallace
Terahertz imaging has been previously shown to be capable of distinguishing normal breast tissue from its cancerous form, indicating its applicability to breast conserving surgery. The heterogeneous composition of breast tissue is among the main challenges to progressing this potential research towards a practical application. In this paper, two concentration analysis methods are proposed for analyzing phantoms mimicking breast tissue. The dielectric properties and the double Debye parameters were used to determine the phantom composition...
March 1, 2018: Biomedical Optics Express
Saroj R Tripathi, Paul Ben Ishai, Kodo Kawase
The applications of terahertz (THz) waves have been increasing rapidly in different fields such as information and communication technology, homeland security and biomedical engineering. However, study on the possible health implications due to various biological effects induced by THz waves is relatively scarce. Previously, it has been reported that the human sweat ducts play a significant role in the interaction of the THz wave with human skin due to its coiled structure. This structure imposes on them the electromagnetic character of a helical antenna...
March 1, 2018: Biomedical Optics Express
O A Smolyanskaya, I J Schelkanova, M S Kulya, E L Odlyanitskiy, I S Goryachev, A N Tcypkin, Ya V Grachev, Ya G Toropova, V V Tuchin
The optical clearing method has been widely used for different spectral ranges where it provides tissue transparency. In this work, we observed the enhanced penetration of the terahertz waves inside biological samples (skin, kidney, and cornea) treated with glycerol solutions inducing changes of optical and dielectric properties. It was supported by the observed trend of free-to-bound water ratio measured by the nuclear magnetic resonance (NMR) method. The terahertz clearing efficiency was found to be less for diabetic samples than for normal ones...
March 1, 2018: Biomedical Optics Express
Xiaohui Han, Shihan Yan, Ziyi Zang, Dongshan Wei, Hong-Liang Cui, Chunlei Du
Protein analysis is the foundation to understanding the mechanisms of complex biological processes. As one of the most widely used techniques to determine protein species and contents, protein dot blot aids biology research but needs corresponding antibodies for marking. A label-free detection method based on terahertz time-domain spectroscopy (THz-TDS) is proposed and demonstrated to improve this traditional technology. A membrane loaded with protein samples is directly scanned using a transmission THz-TDS system for spectral imaging...
March 1, 2018: Biomedical Optics Express
Andrey Fokin, Mikhail Glyavin, German Golubiatnikov, Lev Lubyako, Mikhail Morozkin, Boris Movschevich, Alexander Tsvetkov, Gregory Denisov
Many state-of-the-art fundamental and industrial projects need the use of terahertz radiation with high power and small linewidth. Gyrotrons as radiation sources provide the desired level of power in the sub-THz and THz frequency range, but have substantial free-running frequency fluctuations of the order of 10-4 . Here, we demonstrate that the precise frequency stability of a high-power sub-THz gyrotron can be achieved by a phase-lock loop in the anode voltage control. The relative width of the frequency spectrum and the frequency stability obtained for a 0...
March 12, 2018: Scientific Reports
Chih-Hsien Lai, Yi-Siang Yeh, Chih-An Yeh, Yu-Kun Wang
We numerically investigate the transmission of the antiresonant-reflection-based terahertz (THz) pipe waveguide in which the cladding layer is very thin or the cladding index is close to one. It is found that robustness of the waveguide confinement is maintained when the cladding thickness is small, while the guiding ability deteriorates when the cladding index approaches to one. Hence, to increase the effective bandwidth of the pipe waveguide, reducing the cladding thickness is more desirable. Moreover, we also examine the effective bandwidth under the condition that the pipe waveguide is subject to a fixed ratio of core diameter to cladding thickness...
March 5, 2018: Optics Express
Jia Shi, Yuye Wang, Tunan Chen, Degang Xu, Hengli Zhao, Linyu Chen, Chao Yan, Longhuang Tang, Yixin He, Hua Feng, Jianquan Yao
The imaging diagnosis and prognostication of different degrees of traumatic brain injury (TBI) is very important for early care and clinical treatment. Especially, the exact recognition of mild TBI is the bottleneck for current label-free imaging technologies in neurosurgery. Here, we report an automatic evaluation method for TBI recognition with terahertz (THz) continuous-wave (CW) transmission imaging based on machine learning (ML). We propose a new feature extraction method for biological THz images combined with the transmittance distribution features in spatial domain and statistical distribution features in normalized gray histogram...
March 5, 2018: Optics Express
Jing Wang, Hao Tian, Yu Wang, Xueyan Li, Yujie Cao, Li Li, Jianlong Liu, Zhongxiang Zhou
An electrically tunable terahertz (THz) modulator with large modulation depth and low insertion loss is performed with liquid crystal (LC) metamaterial. The modulation depth beyond 90% and insertion loss below 0.5 dB are achievable at normal incidence by exploiting plasmon-induced transparency (PIT) effect. The PIT spectra can be manipulated by actively controlling the interference between dipole mode and nonlocal surface-Bloch mode with LC. The incident angle tuning effect on PIT spectra shows that the large modulation depth and low insertion loss can remain over a wide range of working angles...
March 5, 2018: Optics Express
Xi Wang, Qian Ma, Leiming Wu, Jun Guo, Shunbin Lu, Xiaoyu Dai, Yuanjiang Xiang
Black phosphorus (BP), a promising new two-dimensional (2D) material, has drawn a lot of attentions in academia and industry due to its extraordinary physical and chemical properties. In this paper, we theoretically demonstrate a monolayer BP that achieves coherent perfect absorption (CPA) at the THz/infrared band. It is found that quasi-CPA point does exist at the THz/infrared band. The CPA, which has a relative bandwidth of 141.3% and a coherent absorptivity of more than 90%, can be implemented at the quasi-CPA wavelength through a proper phase modulation...
March 5, 2018: Optics Express
Corinna L Koch Dandolo, Jean-Paul Guillet, Xue Ma, Frédéric Fauquet, Marie Roux, Patrick Mounaix
Reflection terahertz frequency modulated continuous waves scanner (300 GHz) has been proficiently optimized for imaging two easel paintings of different age. The information content of the obtained THz images has been fully inspected by selecting the appropriate THz image parameter. At the same time, a new data processing has been developed for improving the level of detail held by the axial parametric THz images by means of Gaussian fit of the reflected signals. By carefully weighting the reflected signals as a function of the optical path, the reflected amplitude has been corrected for the positioning of the object surface with respect to the beam focal point...
March 5, 2018: Optics Express
D Mihrin, P W Jakobsen, A Voute, L Manceron, R Wugt Larsen
The high-resolution terahertz absorption spectrum of the large-amplitude intermolecular donor librational band ν of the homodimer (HCN)2 has been recorded by means of long-path static gas-phase Fourier transform spectroscopy at 207 K employing a highly brilliant electron storage ring source. The rovibrational structure of the ν band has the typical appearance of a perpendicular type band of a Σ-Π transition for a linear polyatomic molecule. The generated terahertz spectrum is analyzed employing a standard semi-rigid linear molecule Hamiltonian, yielding a band origin ν0 of 119...
March 12, 2018: Physical Chemistry Chemical Physics: PCCP
Tyler Bowman, Alec Walter, Olga Shenderova, Nicholas Nunn, Gary McGuire, Magda El-Shenawee
THz imaging is effective in distinguishing between cancerous, healthy, and fatty tissues in breast tumors, but a challenge remains in the contrast between cancerous and fibroglandular (healthy) tissues. This work investigates carbon-based nanoparticles as potential contrast agents for terahertz imaging of breast cancer. Microdiamonds, nanodiamonds, and nanometer-scale onion-like carbon are characterized with terahertz transmission spectroscopy in low-absorption backgrounds of polydimethylsiloxane or polyethylene...
October 2017: Biomedical Physics & Engineering Express
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