Thermally controllable filter at terahertz region

Shin, Hee Jun, Min-Cheol Lim, Sae-Hyung Kim, Kisang Park, Sung-Wook Choi, and Gyeongsik Ok. "Thermally controllable filter at terahertz region." Infrared Physics & Technology (2017).

Abstract

We experimentally investigated terahertz (THz) filters fabricated using dodecanoic acid (DDA) particles and polyethylene (PE) by performing THz time-domain spectroscopy. Since the refractive indices of DDA and PE are the same in the THz range, no optical scattering occurred when they were mixed. However, heating caused air voids to replace the DDA particles, and the DDA melted into the spaces between the PE particles. Furthermore, as the DDA particle size, heating time, and DDA content increased, the THz band width became narrower. Based on the results, we propose a new, low-cost type of THz filter with a simple manufacturing method.

......................The THz transmission spectra of the DDA were measured from 0.2 THz to 3 THz (6–100 cm−1) using a commercial THz-TDS system (TPS-3000, Teraview, UK) at room temperature and less than 1% humidity........................................

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https://www.sciencedirect.com/science/article/pii/S1350449517306722

A Study of the Effect of a Protein on the Structure of Water in Solution Using Terahertz Time-Domain Spectroscopy

Penkov, Nikita, Valery Yashin, Eugeny Fesenko Jr, Andrew Manokhin, and Eugeny Fesenko. "A Study of the Effect of a Protein on the Structure of Water in Solution Using Terahertz Time-Domain Spectroscopy." Applied Spectroscopy (2017): 0003702817735551.

Abstract

Terahertz time-domain spectroscopy (THz-TDS) was used to determine the spectra (range ¼ 1.2–120 cm-1 ) of aqueous solutions of bovine serum albumin (BSA) at pH range 2.5–10. Under each of the selected pH, BSA molecules exist in a different conformation, compared to other pH values. The spectra were used to calculate the functions of the dielectric permittivity of BSA solutions. Dielectric functions of the aqueous phase of BSA solutions were calculated based on the Bruggeman model, without the contribution of BSA itself. Fitting of the dielectric functions was performed using a model which includes three water spectral bands: two relaxation bands with relaxation times of about 8.28 and 0.3 ps and a vibrational band with a maximum of about 180 cm-1 . The parameters of these bands were determined through fitting and physical interpretation at the molecular level can be provided for each of them. A comparison between the values of model parameters of solutions with BSA and without BSA allowed to conclude that the main effect of BSA is the formation of strongly bound hydration shells in the immediate proximity to the protein molecule. At the same time, the structure of more distant layers of the hydration shells is destroyed, with an increased formation of free water molecules. Some differences are observed in the effect of different BSA conformations on the aqueous phase of solution. The proposed approach can be generalized and applied for studying of a wide class of biological macromolecules in aqueous solutions. 

… by the spectral properties of the solvent water. The fact is that the absorption coefficient of … TPS Spectra 3000 spectrometer (Teraview, UK) in the wave number range from 1.2 to 120 … of electric field into the spectra was performed using the Blackman–Harris 3 apodization function …

for full paper see http://journals.sagepub.com/doi/pdf/10.1177/0003702817735551

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Excitations and relaxation dynamics in multiferroic GeV 4 S 8 studied by terahertz and dielectric spectroscopy

Reschke, S., Zhe Wang, F. Mayr, E. Ruff, P. Lunkenheimer, V. Tsurkan, and A. Loidl. "Excitations and relaxation dynamics in multiferroic GeV 4 S 8 studied by terahertz and dielectric spectroscopy." Physical Review B 96, no. 14 (2017): 144418

Abstract

We report on THz time-domain spectroscopy on multiferroic GeV4S8, which undergoes orbital ordering at a Jahn-Teller transition at 30.5 K and exhibits antiferromagnetic order below 14.6 K. The THz experiments are complemented by dielectric experiments at audio and radio frequencies. We identify a low-lying excitation close to 0.5 THz, which is only weakly temperature dependent and probably corresponds to a molecular excitation within the electronic level scheme of the V4 clusters. In addition, we detect complex temperature-dependent behavior of a low-lying phononic excitation, closely linked to the onset of orbitally driven ferroelectricity. In the high-temperature cubic phase, which is paramagnetic and orbitally disordered, this excitation is of relaxational character becomes an overdamped Lorentzian mode in the orbitally ordered phase below the Jahn-Teller transition, and finally appears as well-defined phonon excitation in the antiferromagnetic state. Abrupt changes in the real and imaginary parts of the complex dielectric permittivity show that orbital ordering appears via a structural phase transition with strong first-order character and that the onset of antiferromagnetic order is accompanied by significant structural changes, which are of first-order character, too. Dielectric spectroscopy documents that at low frequencies, significant dipolar relaxations are present in the orbitally ordered, paramagnetic phase only. In contrast to the closely related GaV4S8, this relaxation dynamics that most likely mirrors coupled orbital and polar fluctuations does not seem to be related to the dynamic processes detected in the THz regime.

… The time-domain THz transmission experiments using a TPS Spectra 3000 spectrometer

for full paper see https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.144418

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Vibrational states of nano-confined water molecules in beryl investigated by first-principles calculations and optical experiments

Belyanchikov, Mikhail, Elena Zhukova, Sergei Tretiak, Andriy Zhugayevych, Martin Dressel, Frank Uhlig, Jens Smiatek, Maria Fyta, Victor G. Thomas, and Boris Gorshunov. "Vibrational states of nano-confined water molecules in beryl investigated by first principles calculations and optical experiments." Physical Chemistry Chemical Physics (2017).

Abstract

Using quantum mechanical calculations within density functional theory, we provide a comprehensive analysis of infrared-active excitation of water molecules confined in nanocages of a beryl crystal lattice. We calculate infrared-active modes including the translational, librational, and mixed-type resonances of regular and heavy water molecules. The results are compared to the experimental spectra measured for the two principal polarizations of the electric field: parallel and perpendicular to the crystallographic c-axis. Good agreement is achieved between calculated and measured isotopic shifts of the normal modes. We analyze the vibrational modes in connection with the structural characteristics and arrangements of water molecules within the beryl crystal. Specific atomic displacements are assigned to each experimentally detected vibrational mode resolving the properties of nano-confined water on scales not accessible by experiments. Our results elucidate the applicability and efficiency of a combined experimental and computational approach for describing and an in-depth understanding of nano-confined water, and pave the way for future studies of more complex systems.

... dielectric permittivity and optical conductivity were directly determined using quasioptical
spectrometer based on monochromatic and continuously frequency tunable radiation generators –
backward- wave oscillators 33 and a pulsed THz time-domain teraview TPS Spectra ...

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for full paper see http://pubs.rsc.org/en/content/articlelanding/2017/cp/c7cp06472a/unauth#!divAbstract

Global mapping of stratigraphy of an old-master painting using sparsity-based terahertz reflectometry

Dong, Junliang, Alexandre Locquet, Marcello Melis, and D. S. Citrin. "Global mapping of stratigraphy of an old-master painting using sparsity-based terahertz reflectometry." Scientific Reports 7, no. 1 (2017): 15098.

Abstact

The process by which art paintings are produced typically involves the successive applications of preparatory and paint layers to a canvas or other support; however, there is an absence of nondestructive modalities to provide a global mapping of the stratigraphy, information that is crucial for evaluation of its authenticity and attribution, for insights into historical or artist-specific techniques, as well as for conservation. We demonstrate sparsity-based terahertz reflectometry can be applied to extract a detailed 3D mapping of the layer structure of the 17th century easel painting Madonna in Preghiera by the workshop of Giovanni Battista Salvi da Sassoferrato, in which the structure of the canvas support, the ground, imprimatura, underpainting, pictorial, and varnish layers are identified quantitatively. In addition, a hitherto unidentified restoration of the varnish has been found. Our approach unlocks the full promise of terahertz reflectometry to provide a global and detailed account of an easel painting’s stratigraphy by exploiting the sparse deconvolution, without which terahertz reflectometry in the past has only provided a meager tool for the characterization of paintings with paint-layer thicknesses smaller than 50 μm. The proposed modality can also be employed across a broad range of applications in nondestructive testing and biomedical imaging.

.......Methods. THz reflective imaging. A typical THz time-domain system (Teraview TPS Spectra 3000) is employed in this study............ 

for full paper see

https://www.nature.com/articles/s41598-017-15069-2

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