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Cathy Ridgway, Prince Bawuah, Daniel Markl, J Axel Zeitler, Jarkko Ketolainen, Kai-Erik Peiponen, Patrick Gane
The physical properties and mechanical integrity of pharmaceutical tablets are of major importance when loading with active pharmaceutical ingredient(s) (API) in order to ensure ease of processing, control of dosage and stability during transportation and handling prior to patient consumption. The interaction between API and excipient, acting as functional extender and binder, however, is little understood in this context. The API indomethacin is combined in this study with microcrystalline cellulose (MCC) at increasing loading levels...
April 18, 2017: International Journal of Pharmaceutics
Fabio Novelli, Saeideh Ostovar Pour, Jonathan O Tollerud, Ashkan Roozbeh, Dominique R T Appadoo, Ewan W Blanch, Jeffrey A Davis
Here we reveal details of the interaction between human lysozyme proteins, both native and fibrils, and their water environment by intense terahertz time domain spectroscopy. With the aid of a rigorous dielectric model, we determine the amplitude and phase of the oscillating dipole induced by the THz field in the volume containing the protein and its hydration water. At low concentrations, the amplitude of this induced dipolar response decreases with increasing concentration. Beyond a certain threshold, marking the onset of the interactions between the extended hydration shells, the amplitude remains fixed but the phase of the induced dipolar response, which is initially in phase with the applied THz field, begins to change...
April 21, 2017: Journal of Physical Chemistry. B
Tianying Chang, Xiansheng Zhang, Xiaoxuan Zhang, Hong-Liang Cui
Interactions of terahertz (THz) electromagnetic radiation with polymer materials have been studied recently with increasing depth and breadth, for purposes of both using polymers in fabricating THz optical components such as lenses, waveplates, waveguides, and sample holders/containers, and employing THz spectral imaging as a new tool for nondestructive testing of polymer composite structures. Either endeavor cannot even begin without a quantitative knowledge of the complex dielectric permittivity, i.e., the propagation and attenuation properties of such polymers in the requisite wave band...
April 20, 2017: Applied Optics
Kawsar Ahmed, Sawrab Chowdhury, Bikash Kumar Paul, Md Shadidul Islam, Shuvo Sen, Md Ibadul Islam, Sayed Asaduzzaman
In this paper, a novel polarization-maintaining single-mode photonic crystal fiber (PCF) has been suggested for terahertz (THz) transmission applications. The reported PCF has five layers of hexagonal cladding with two layers of porous core. The cladding and core territory of the PCF are constituted by circular and elliptical air cavities, accordingly acting as a dielectric medium. Different geometrical parameters of the proposed PCF including pitches and diameters of circular air holes with the major and minor axes of elliptical air cavities being varied with the optimized structure...
April 20, 2017: Applied Optics
H W Hou, Z Liu, J H Teng, T Palacios, S J Chua
In this work, a high temperature THz detector based on a GaN high electron mobility transistor (HEMT) with nano antenna structures was fabricated and demonstrated to be able to work up to 200( )°C. The THz responsivity and noise equivalent power (NEP) of the device were characterized at 0.14 THz radiation over a wide temperature range from room temperature to 200 °C. A high responsivity Rv of 15.5 and 2.7 kV/W and a low NEP of 0.58 and 10 pW/Hz(0.5) were obtained at room temperature and 200 °C, respectively...
April 21, 2017: Scientific Reports
Deliang Zhou, Liwei Hou, Wei Xie, Yuanzhang Zang, Bin Lu, Jian Chen, Peiheng Wu
This paper introduces a dual-band terahertz imaging system as a potential product for nondestructive testing using heterodyne detectors and continuous-wave sources. The operating frequencies of the system are 110.4 and 220.8 GHz. Multiband fusion technology combines the advantages of the greater spatial resolution of the high-frequency band and the enhanced sensitivity of the low-frequency band to improve the detection ability of the system. Additionally, the interference cancellation technology is used to obtain a superior image quality...
April 10, 2017: Applied Optics
Sandeep Inampudi, Jierong Cheng, Hossein Mosallaei
High-resolution and fast-paced optical microscopy is a requirement for current trends in biotechnology and materials industry. The most reliable and adaptable technique so far to obtain higher resolution than conventional microscopy is near-field scanning optical microscopy (NSOM), which suffers from a slow-paced nature. Stemming from the principles of diffraction imaging, we present fast-paced graphene-based scanning-free wide-field optical microscopy that provides image resolution that competes with NSOM...
April 10, 2017: Applied Optics
Siqi Yan, Ziwei Cheng, Lars Hagedorn Frandsen, Yunhong Ding, Feng Zhou, Jianji Dong, Xinliang Zhang
A photonic differentiator (DIFF) plays a crucial role in photonic circuits. Despite the fact that a DIFF having a terahertz bandwidth has been reported, the practical bandwidth is limited to being a bandpass response. In this Letter, we propose the concept of a bandwidth-adaptable DIFF, which exploits the slow light effect in a photonic crystal waveguide (PhCW) to overcome the inherent bandwidth limitation of current photonic DIFFs. We fabricated a PhCW Mach-Zehnder interferometer (PhCW-MZI) on the silicon-on-isolator material platform to validate our concept...
April 15, 2017: Optics Letters
Mu-Chieh Lo, Robinson Guzmán, Carlos Gordón, Guillermo Carpintero
This Letter presents a photonics-based millimeter wave and terahertz frequency synthesizer using a monolithic InP photonic integrated circuit composed of a mode-locked laser (MLL) and two pulse interleaver stages to multiply the repetition rate frequency. The MLL is a multiple colliding pulse MLL producing an 80 GHz repetition rate pulse train. Through two consecutive monolithic pulse interleaver structures, each doubling the repetition rate, we demonstrate the achievement of 160 and 320 GHz. The fabrication was done on a multi-project wafer run of a generic InP photonic technology platform...
April 15, 2017: Optics Letters
Daniel Markl, Samy Yassin, D Ian Wilson, Daniel J Goodwin, Andrew Anderson, J Axel Zeitler
Oral dosage forms are an integral part of modern health care and account for the majority of drug delivery systems. Traditionally the analysis of the dissolution behaviour of a dosage form is used as the key parameter to assess the performance of a drug product. However, understanding the mechanisms of disintegration is of critical importance to improve the quality of drug delivery systems. The disintegration performance is primarily impacted by the hydration and subsequent swelling of the powder compact. Here we compare liquid ingress and swelling data obtained using terahertz pulsed imaging (TPI) to a set of mathematical models...
April 8, 2017: International Journal of Pharmaceutics
Hongbin Zhang, Baoyuan Man, Qi Zhang
Due to the gapless surface state and narrow bulk band gap, the light absorption of topological crystalline insulators covers a broad spectrum ranging from terahertz to infrared, revealing promising applications in new generation optoelectronic devices. To date, the photodetectors based on topological insulators generally suffer from a large dark current and a weaker photocurrent especially under the near-infrared lights, which severely limits the practical application of devices. Owing to the lower excitation energy of infrared lights, the photodetection application of topological crystalline insulators in the near-infrared region relies critically on understanding the preparation and properties of their heterostructures...
April 14, 2017: ACS Applied Materials & Interfaces
Heng-He Tang, Tie-Jun Huang, Jiang-Yu Liu, Yunhua Tan, Pu-Kun Liu
The resolution of conventional terahertz (THz) imaging techniques is limited to about half wavelength, which is not fine enough for applications of biomedical sensing and nondestructive testing. To improve the resolution, a new superlens, constructed by a monolayer graphene sheet combining with a grating voltage gate, are proposed in this paper to achieve deep super-resolution imaging in the THz frequency range. The main idea is based on the Fabry-Perot resonance of graphene edge plasmon waves. By shaping the voltage gate into a radial pattern, magnified images of subwavelength targets can be obtained...
April 11, 2017: Scientific Reports
Weien Lai, Oday Mazin Abdulmunem, Pablo Del Pino, Beatriz Pelaz, Wolfgang J Parak, Qian Zhang, Huaiwu Zhang
This paper presents a significant effect of manganese ferrite nanoparticles (MnFe2O4 NPs) on the increase of the surface photoconductivity of semiconductors. Herein, the optical characterization of photo-excited carriers of silicon coated with MnFe2O4 NPs was studied by using THz time-domain spectroscopy (THz-TDs). We observed that silicon coated with MnFe2O4 NPs provided a significantly enhanced attenuation of THz radiation in comparison with bare silicon substrates under laser irradiation. The experimental results were assessed in the context of a surface band structure model of semiconductors...
April 10, 2017: Scientific Reports
Mohsen Sajadi, Martin Wolf, Tobias Kampfrath
Collective low-frequency molecular motions have large impact on chemical reactions and structural relaxation in liquids. So far, these modes have mostly been accessed indirectly by off-resonant optical pulses. Here, we provide evidence that intense terahertz (THz) pulses can resonantly excite reorientational-librational modes of aprotic and strongly polar liquids through coupling to the permanent molecular dipole moments. We observe a significantly enhanced response because the transient optical birefringence is up to an order of magnitude higher than obtained with optical excitation...
April 10, 2017: Nature Communications
Basanth S Kalanoor, Maria Ronen, Ziv Oren, Doron Gerber, Yaakov R Tischler
The low-frequency vibrational (LFV) modes of biomolecules reflect specific intramolecular and intermolecular thermally induced fluctuations that are driven by external perturbations, such as ligand binding, protein interaction, electron transfer, and enzymatic activity. Large efforts have been invested over the years to develop methods to access the LFV modes due to their importance in the studies of the mechanisms and biological functions of biomolecules. Here, we present a method to measure the LFV modes of biomolecules based on Raman spectroscopy that combines volume holographic filters with a single-stage spectrometer, to obtain high signal-to-noise-ratio spectra in short acquisition times...
March 31, 2017: ACS Omega
H J Qin, Kh Zakeri, A Ernst, J Kirschner
When an ordered spin system of a given dimensionality undergoes a second order phase transition, the dependence of the order parameter, i.e., magnetization on temperature, can be well described by thermal excitations of elementary collective spin excitations (magnons). However, the behavior of magnons themselves, as a function of temperature and across the transition temperature T_{C}, is an unknown issue. Utilizing spin-polarized high resolution electron energy loss spectroscopy, we monitor the high-energy (terahertz) magnons, excited in an ultrathin ferromagnet, as a function of temperature...
March 24, 2017: Physical Review Letters
Zelin Dai, Xiangdong Xu, Yu Gu, Xinrong Li, Fu Wang, Yuxiang Lian, Kai Fan, Xiaomeng Cheng, Zhegeng Chen, Minghui Sun, Yadong Jiang, Chun Yang, Jimmy Xu
The low-frequency characteristics of polycrystalline taurine were studied experimentally by terahertz (THz) absorption spectroscopy and theoretically by ab initio density-functional simulations. Full optimizations with semi-empirical dispersion correction were performed in spectral computations and vibrational mode assignments. For comparison, partial optimizations with pure density functional theory were conducted in parallel. Results indicate that adding long-range dispersion correction to the standard DFT better reproduces the measured THz spectra than the popular partial optimizations...
March 28, 2017: Journal of Chemical Physics
Kirill A Grishunin, Nikita A Ilyin, Natalia E Sherstyuk, Elena D Mishina, Alexey Kimel, Vladimir M Mukhortov, Andrey V Ovchinnikov, Oleg V Chefonov, Mikhail B Agranat
Second Harmonic Generation induced by the electric field of a strong nearly single-cycle terahertz pulse with the peak amplitude of 300 kV/cm is studied in a classical inorganic ferroelectric thin film of (Ba0.8Sr0.2)TiO3. The dependences of the SHG intensity on the polarization of the incoming light is revealed and interpreted in terms of electric polarization induced in the plane of the film. As the THz pulse pumps the medium in the range of phononic excitations, the induced polarization is explained as a dynamical change of the ferrolectric order parameter...
April 6, 2017: Scientific Reports
Mohammad Ali Khosrovani Moghaddam, Mehdi Ahmadi-Boroujeni
The effect of dielectric cladding on the waveguiding characteristics of an array of metallic pillars on a metal plane in the sub-terahertz band is explored. Firstly, a 2D structure made up of a metallic grating of infinite lateral width with various dielectric overlays is analytically studied to get more insight into the problem. Then the ideas inferred from the 2D structure are applied to the realistic 3D structure that has a finite lateral width. It is shown that by proper design of the dielectric medium surrounding the metallic structure the modal field confinement can be enhanced in a broad frequency band resulting in a low bending loss...
March 20, 2017: Optics Express
Arno Rehn, David Jahn, Jan C Balzer, Martin Koch
An extensive investigation of the origin and the impact of periodic sampling errors of terahertz time-domain spectroscopy systems is given. We present experimental findings and compare them to a theoretical model which is developed in this work. Special attention is given to the influence on the extraction of the refractive index from measurements. It can be shown that even distortions of the spectrum at frequencies higher than the used bandwidth can have a significant impact on the extracted refractive index...
March 20, 2017: Optics Express
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