Properties of two-component nematic liquid crystal mixtures in the range of 0.3–3.0 THz

TeraView's TPS Spectra 3000 was used to investigate nematic liquid crystals in the range of 0.3–3.0 THz.


http://www.tandfonline.com/doi/abs/10.1080/02678292.2015.1036816#.VYvdFvlViko


Abstract

In this work, we present the results of terahertz measurements of five nematic liquid crystal materials. Optical properties like refractive indices, birefringence and absorption coefficients of liquid crystals (LCs) for ordinary and extraordinary polarisation were compared. The aim of this study was to check the impact of the structure of LC molecules on above properties. The compounds with different core structure and various number of laterally substituted fluorine atoms were chosen. A standard terahertz Time-Domain Spectrometer to measurements from 0.3 THz to 3 THz was used.

TeraView TPS 3000 unit for time domain spectroscopy was used to investigate spectral properties of nematic liquid crystal mixtures

Article

Spectral Properties of Nematic Liquid Crystal Mixtures Composed with Long and Short Molecules in THz Frequency Range

ABSTRACT In this paper the influence of short and long molecules added to liquid crystal
6CHBT were investigated. Change of refractive indices and absorption coefficients
for 6CHBT mixtures were compared in the 0.3 - 3 THz frequency range. Influence of
temperature on the mentioned parameters of liquid crystal were investigated. Our study
show that even a slight change in shape and the composition of the molecules dopants
affects the macroscopic properties of liquid crystal. These properties depend on the
length of chains, the number of benzene or cyclohexane rings or the spatial distribution
of molecules and the interactions between them in the liquid crystal mixture. Spectra
measurements on the terahertz time-domain spectrometer were performed.
Spectral Properties of Nematic Liquid Crystal Mixtures Composed with Long and Short Molecules in THz Frequency Range (PDF Download Available). Available from: http://www.researchgate.net/publication/235218799_Spectral_Properties_of_Nematic_Liquid_Crystal_Mixtures_Composed_with_Long_and_Short_Molecules_in_THz_Frequency_Range [accessed Jun 23, 2015].

Terahertz single conductance quantum and topological phase transitions in topological insulator Bi2Se3 ultrathin films

Byung Cheol Park, Tae-Hyeon Kim, Kyung Ik Sim, Boyoun Kang, Jeong Won Kim, Beongki Cho, Kwang-Ho Jeong, Mann-Ho Cho & Jae Hoon Kim

Abstract

Strong spin-orbit interaction and time-reversal symmetry in topological insulators generate novel quantum states called topological surface states. Their study provides unique opportunities to explore exotic phenomena such as spin Hall effects and topological phase transitions, relevant to the development of quantum devices for spintronics and quantum computation. Although ultrahigh-vacuum surface probes can identify individual topological surface states, standard electrical and optical experiments have so far been hampered by the interference of bulk and quantum well states. Here, with terahertz time-domain spectroscopy of ultrathin Bi2Se3 films, we give evidence for topological phase transitions, a single conductance quantum per topological surface state, and a quantized terahertz absorbance of 2.9% (four times the fine structure constant). Our experiment demonstrates the feasibility to isolate, detect and manipulate topological surface states in the ambient at room temperature for future fundamental research on the novel physics of topological insulators and their practical applications.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.nature.com/ncomms/2015/150316/ncomms7552/full/ncomms7552.html#figures

Analysis of the Terahertz Absorption Spectrum of Melamine

Yeun Hee Hwang, Yo Han Noh, Dongkyun Seo, Hak Min Yeo, Seongheun Kim, Jaehun Park, Hyang Sook Chun, and Kyungwon Kwak

Abstract

In this paper, with terahertz (THz) time-domain spectroscopy, we measure the characteristic absorption peaks of melamine and analyze their vibrational modes with the help of solid-state density functional theory (DFT) calculations. The observed strong absorption peaks at 2, 2.27, and 2.61 THz are well reproduced but show red shifts compared to the theoretical results. Detailed normal mode analyses are carried out, which reveals that those THz peaks are generated from intermolecular vibrations. Temperature-dependent THz measurements suggest that this red shift mainly comes from the temperature effect. Thus, three peaks are assigned to the calculated intermolecular vibrational motions. This result indicates that THz spectroscopy can be a useful tool to detect the details of intermolecular structures.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://onlinelibrary.wiley.com/doi/10.1002/bkcs.10166/abstract?systemMessage=Wiley+Online+Library+will+be+disrupted+on+7th+March+from+10%3A00-13%3A00+GMT+%2805%3A00-08%3A00+EST%29+for+essential+maintenance.++Apologies+for+the+inconvenience.&userIsAuthenticated=false&deniedAccessCustomisedMessage

Polymorphism of Resorcinol Explored by Complementary Vibrational Spectroscopy (FT-RS, THz-TDS, INS) and First Principles Solid-State Computations (Plane-Wave DFT)

Kacper Druzbicki , Edward Mikuli , Norbert Pałka , Sławomir Zalewski , and Mirosława Danuta Ossowska-Chruściel

Abstract

The polymorphism of resorcinol has been complementary studied by combining Raman, time-domain terahertz and inelastic neutron scattering spectroscopy with modern solid-state density functional theory (DFT) calculations. The spectral differences, emerging from the temperature-induced structural phase transition, have been successfully interpreted with an emphasis on the low-wavenumber range. The given interpretation is based on the plane-wave DFT computations, providing an excellent overall reproduction of both wavenumbers and intensities and revealing the source of the observed spectral differences. The performance of the generalized gradient approximation (GGA) functionals in prediction of the structural parameters and the vibrational spectra of the normal-pressure polymorphs of resorcinol has been extensively examined. The results show that standard PBE along with its ‘hard’ revised form tend to be superior if compared to the ‘soft’ GGA approximation.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://pubs.acs.org/doi/abs/10.1021/jp507241j

Terahertz time-domain spectroscopy for measurement of particle sizes of fexofenadine hydrochloride

Anna Sadloňová, Vojtech Kresalek, Tomas Bata

Abstract

Time domain spectroscopy is one of the new methods of terahertz radiation used for wide spectrum of the industry. More extended sector is the security system much like the sector of the medicine. The main focus is orientated to detection and identification of the substances. This study is focused on the measurement of the particle size of pharmaceuticals. The characteristic absorption features will be studied experimentally by Terahertz time-domain spectroscopy. The results are identified for processing by one of the statistical method usable for such variable groups. The three samples of the pharmaceutical– Fexofenadine Hydrochloride (antihistamine) will be compared between themselves. Mentioned samples are supplied by different suppliers. The main focus will be put on the pharmaceutical differences of the same pharmaceutical that are commonly available on the markets. Terahertz time-domain spectroscopy setup was used to measure absorbance spectra of each sample in the range from 1 THz to 3 THz (it was used the device TPS Spectra 3000 produced by TeraView Ltd . The device that belongs to the first commercial machine developed in this company for measurement of the substances by transmission spectroscopy method.). During the testing was used the vacuum for purging the measurement chamber from water vapors.

This study was performed using TeraView's Spectra 3000 system. (TeraView, Cambridge, UK)

Use of Finite Difference Time Domain Simulations and Debye Theory for Modelling the Terahertz Reflection Response of Normal and Tumour Breast Tissue

Anthony J. Fitzgerald, Emma Pickwell-MacPherson, Vincent P. Wallace

Abstract

The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 0.98) and less so for normal breast (p = 0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues.

This study was performed using TeraView's TPS spectra 1000 system. (TeraView, Cambridge, UK)

Full Article: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0099291#pone-0099291-g005

Terahertz time-domain spectroscopy for measurement of particle sizes of fexofenadine hydrochloride

Anna Sadloňová, Vojtech Kresalek, Tomas Bata

Abstract

Time domain spectroscopy is one of the new methods of terahertz radiation used for wide spectrum of the industry. More extended sector is the security system much like the sector of the medicine. The main focus is orientated to detection and identification of the substances. This study is focused on the measurement of the particle size of pharmaceuticals. The characteristic absorption features will be studied experimentally by Terahertz time-domain spectroscopy. The results are identified for processing by one of the statistical method usable for such variable groups. The three samples of the pharmaceutical– Fexofenadine Hydrochloride (antihistamine) will be compared between themselves. Mentioned samples are supplied by different suppliers. The main focus will be put on the pharmaceutical differences of the same pharmaceutical that are commonly available on the markets. Terahertz time-domain spectroscopy setup was used to measure absorbance spectra of each sample in the range from 1 THz to 3 THz (it was used the device TPS Spectra 3000 produced by TeraView Ltd . The device that belongs to the first commercial machine developed in this company for measurement of the substances by transmission spectroscopy method.). During the testing was used the vacuum for purging the measurement chamber from water vapors.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://spie.org/ESD/conferencedetails/millimetre-wave-and-terahertz-sensors-and-technology

Distinguishing of different kinds of gunpowder using various methods based on Terahertz radiation

Tomáš Gavenda, Vojtech Kresalek, Tomas Bata

Abstract

The research performed by authors of this article in the year 2013 [1] lead to the following presented research. Different samples of commercially known kinds of gunpowder prepared by various manufactures were measured to obtain presented data. The article published in 2013 [1] proved, that particular samples can be distinguished from each other using terahertz time-domain spectroscopy. This article presents results of measuring and analysing of gunpowder samples using other methods based on terahertz radiation. Ten different samples of gunpowder were measured during the research. Most of them were based on nitrocellulose, but components of each sample differ. Systems TPS Spectra 3000 by TeraView Ltd. and Tera OSCAT by Menlo GmbH. were used for measurements. Several terahertz radiation based methods were used for researching the possibility of distinguishing different kinds of gunpowder, such as terahertz imaging (using both transitive and reflective imaging method), ATR spectroscopy and reflective variant of time-domain spectroscopy. Frequency ranges differ in dependence on used method, but the range from 0.5 THz to 2.0 THz was measured mostly. Presented research also contains results of measurements of gunpowder compounds, for example compounds with polymer materials (like polyethylene). These measurements are important because of the need for development of new possibilities to detect and identify dangerous materials at airports or other public places. Main contribution of this research is extension of knowledge in the domain of detection, identification and distinguishing of different kinds of gunpowder, which are commercially available and therefore exploitable as dangerous explosive materials. This article, together with the previous presented and already published article [1], makes comprehensive result of gunpowder properties measurement using methods based on terahertz radiation. [1] Gavenda T., Kresalek V., “Terahertz time-domain spectroscopy for distinguishing different kinds of gunpowder,” Proc. SPIE 8900, 6 pages (2013).

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://spie.org/ESD/conferencedetails/millimetre-wave-and-terahertz-sensors-and-technology

Terahertz radiation NDE of composite materials for wind turbine applications

Je-Woong Park, Kwang-Hee Im, In-Young Yang, Sun-Kyu Kim, Sung-Jun Kang, Young-Tae Cho, Jong-An Jung, David Kuei Hsu

Abstract

Nondestructive testing technique using T-ray (terahertz ray) has received more interest as a new capability tool in engineering application. So, T-ray time-domain spectroscopy was used for inspecting and evaluating physical property and defect characteristics in FRP composite materials for a use of wind energy. First of all, a general refraction mode and transmission mode was utilized for calculating a refractive index (n) based on the well-machined sample. In order to obtain the terahertz ray refractive index, a refractive mode and a transmission mode technique was defined for solving a refractive coefficient (n), with which refractive index of GFRP composites, balsa and epoxy for a use of wind turbine blades could be obtained. A method of wind turbine blade composites having one and two saw-cuts delaminations and some angles/directions was suggested based on the E-field vector. The time of flight in T-ray using evaluating a T-ray transmission mode agreed with that using T-ray time-domain spectroscopy with the wind turbine blade. Also, in CFRP composites, T-ray propagation is limited because the carbon fibers are blocking the T-ray. Therefore, we have analyzed difference between E-field vector in T-ray and the carbon fiber direction. Also, it was found that a T-ray time domain data in thick GFRP composite laminates seemed to show peaks with a regular spacing (Δt) which was obvious with the close relation between TOF and FFT.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://link.springer.com/article/10.1007/s12541-014-0464-0

Chemometrics Applied to Quantitative Analysis of Ternary Mixtures by Terahertz Spectroscopy

Josette El Haddad , Frederick de Miollis , Joyce Bou Sleiman , Lionel Canioni , Patrick Mounaix , and Bruno Bousquet

Abstract

Chemometrics was applied to qualitative and quantitative analyses of terahertz spectra obtained in transmission mode. A series of mixtures of three pure analytes, namely, citric acid, d-(−)fructose, and α-lactose monohydrate under various concentrations, was prepared as pressed pellets with polyethylene as binder. Then, terahertz absorbance spectra were recorded by terahertz time domain spectroscopy and analyzed. First, principal component analysis allowed one to correctly locate the samples into a ternary diagram. Second, quantitative analysis was achieved by partial least-squares (PLS) regression and artificial neural networks (ANN). The concentrations were predicted with values of relative mean square error lower than 0.9% for the three constituents. As a conclusion, chemometrics was demonstrated to be very efficient for the analysis of the ternary mixtures prepared for this study.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://pubs.acs.org/doi/abs/10.1021/ac500253b

Electrothermally actuated microelectromechanical systems based omega-ring terahertz metamaterial with polarization dependent characteristics

Chong Pei Ho, Prakash Pitchappa, Yu-Sheng Lin, Chia-Yi Huang, Piotr Kropelnicki and Chengkuo Lee

Abstract

We present the design, simulation, fabrication, and characterization of a continuously tunable Omega-ring terahertz metamaterial. The tunability of metamaterial is obtained by integratingmicroactuators into the metamaterial unit cell. Electrothermal actuation mechanism is used to provide higher tuning range, larger stroke, and enhanced repeatability. The maximum achieved tuning range for the resonant frequency is around 0.30 THz for the input power of 500 mW. This shows the potential of using electrothermally actuated microactuators based tunablemetamaterial design for application such as filters, absorbers, sensors, and spectral imagers.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://scitation.aip.org/content/aip/journal/apl/104/16/10.1063/1.4871999

Abstract accepted for an oral presentation at the LACONA-X conference

Tiphaine Bardon from University College London (UCL), who TeraView are currently hosting, has had an abstract accepted for an oral presentation at the LACONA-X conference (Lasers in the Conservation of Artworks) held in the United Arab Emirates between the 9th and the 13th of June 2014, gathering both researchers, conservators and conservation scientists. 

The topic of the presentation will be "Contrast and readability in terahertz time-domain images of ink inscriptions: A comparative study of model and historical documents"


Tiphaine Bardon, Robert K. May, Bianca Jackson, Philip F. Taday, Gerrit De Bruin, Matija Strlič

Abstract

The terahertz range between 0.15 – 3 THz (i.e. 5 – 100 cm-1) has been made accessible due to the development of ultra-short pulse lasers, as the emission and reception of a radiation with such broad bandwidth in the high frequency domain rely on photoconductive semiconductors gated by femtosecond laser pulses.

Terahertz time-domain imaging can give in-depth contrasted images of each layer in a laminar structure, with a depth resolution of up to 30 μm and a penetration depth of a few mm in dry organic materials. The image contrast of a specific layer relies on the differences of absorption and dispersion of the terahertz pulse by the materials on each side of this layer. Documents are, in essence, laminar structures consisting of layers of support (paper or parchment), ink and air gaps. Terahertz time-domain imaging therefore represents an ideal tool for the study of historical documents, the condition of which may prevent their opening or excessive handling, provided that ink inscriptions and their surrounding support can be differentiated in the terahertz image.

This comparative spectroscopic and imaging study of various model inks on different supports demonstrates the independent and combined influence of the nature of both the ink and the support on the contrast of inscriptions seen in terahertz images. Lamp black pigment is found to intensively absorb terahertz radiation and, as a result, any inscription containing lamp black would show good contrast in terahertz images, regardless of the nature of the support. On the other hand, the refractive index of the red pigment vermilion varies greatly in the terahertz region and is similar to the refractive index of parchment at specific frequencies: the image contrast of vermilion inscriptions on parchment is therefore very frequency-dependent.

Other factors can influence the contrast in terahertz images of documents and are reported in the present work: the roughness of the support can induce scattering of the impinging terahertz radiation, the indentation left by a quill or a pen locally modifies both the surface profile and the density (and therefore the refractive index of the support), and the ink penetration into the support creates a refractive index gradient. Finally, good readability of ink inscriptions does not rely solely on the contrast of the image, but also on the spatial resolution of the imaging set-up with respect to the width of the ink inscriptions: spatial resolutions of different set-ups are discussed, together with the loss of spatial resolution when imaging deep into a stack of sheets, depending on the nature and thickness of the supports.

Improved interpretation of the contrast in terahertz images of historical documents is possible on the basis of these findings. As an example, terahertz imaging of an Ottoman document from the UCL Centre for Sustainable Heritage Historic Reference Material Collection, dating from 1870 AD, is discussed: the difference in contrast of two black inscriptions is discussed and corroborated by results of analysis with optical coherence tomography, attenuated Fourier-transform infrared spectroscopy and near-infrared spectroscopy.

Further information about the conference can be found on the conference website:

http://www.lacona10.org/

Terahertz electrodynamics and superconducting energy gap of NbTiN

Taeyoon Hong¹, Kyujin Choi¹, Kyung Ik Sim¹, Taewoo Ha¹, Byung Cheol Park¹,Hirotake Yamamori² and Jae Hoon Kim^1,a)

Abstract

Terahertz electrodynamics of superconducting NbTiN has been studied in the spectral range of 8-70 cm^–1 above and below the critical temperature of Tc  = 14.1 K. Our transmission terahertz time-domain spectroscopy technique allows for independent and accurate determination of both the real part σ1 and the imaginary part σ2 of the optical conductivity σ as a function of frequency ω and temperature T without a Kramers-Kronig analysis. A clear signature of the superconducting energy gap Δ(T) is observed in the real part σ1 of the optical conductivity belowTc , with 2Δ(0) = 36.5 cm⁻¹ corresponding to 2Δ(0)/kBTc  = 3.72. No indication of strong-coupling effects was observed in the imaginary part σ2 toward zero frequency. Our results, including the temperature dependence of the penetration depth λ(T), are in excellent quantitative agreement with weak coupling BCS theory and Mattis-Bardeen formula.

This study was performed using TeraView's TPS Spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://scitation.aip.org/content/aip/journal/jap/114/24/10.1063/1.4856995

Detailed non-destructive evaluation of UHMWPE composites in the terahertz range

Optical and Quantum ElectronicsDOI 10.1007/s11082-013-9836-4

N. Palka, D. Miedzinska

Abstract

We report on the terahertz analysis of an internal structure of an ultra-high molecular weight polyethylene (UHMWPE) composite material, which is based on the HB10-tape from Dyneema®. This type of composite is very hard and resistant and therefore it is often used to manufacture personal armors such as bulletproof vests and helmets. The multilayer structure of the UHMWPE composite was investigated by means of a raster scanning time domain spectroscopy technique in a reflection configuration. The mechanism of the formation of many shifted in time THz pulses (reflected from the internal layers of the sample) originates from the periodic modulation of the refractive index along the propagation of the radiation. This modulation is connected with alternate layers of fibers, each having different direction (perpendicular to each other). As a result we obtained the detailed three dimensional profile of the 3.3-mm thick sample with all 74 layers clearly visible. Thicknesses of all layers, having around 45 μm each, were determined. Moreover, it is also possible to identify internal defects i.e. delaminations in the internal structure of this composite material.

This study was performed using TeraView's TPS Spectra 3000 system, with the XY Reflectance imaging module. (TeraView, Cambridge, UK)


Source: http://link.springer.com/article/10.1007%2Fs11082-013-9836-4/fulltext.html

Terahertz Conductivity of Twisted Bilayer Graphene

Physical Review Letters 110, 067401 (2013)  Received 9 April 2012; published 7 February 2013
doi:10.1103/PhysRevLett.110.067401

Authors: Xingquan Zou1, Jingzhi Shang¹, Jianing Leaw¹, Zhiqiang Luo¹, Liyan Luo¹, Chan La-o-vorakiat¹, Liang Cheng¹, S. A. Cheong¹, Haibin Su², Jian-Xin Zhu³, Yanpeng Liu⁴, Kian Ping Loh⁴, A. H. Castro Neto⁵, Ting Yu¹, and Elbert E. M. Chia¹

1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore
2. Division of Materials Science, School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore
3. Theoretical Division and Center for Integrated Nanotechnologies, +Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
4. Department of Chemistry, +National University of Singapore , 3 Science Drive 3, 117543 Singapore
5. Graphene Research Centre and Physics Department, National University of Singapore, 6 Science Drive 2, 117546 Singapore

More details at: http://prl.aps.org/abstract/PRL/v110/i6/e067401

Abstract

Using terahertz time-domain spectroscopy, the real part of optical conductivity [σ1(ω)] of twisted bilayer graphene was obtained at different temperatures (10–300 K) in the frequency range 0.3–3 THz. On top of a Drude-like response, we see a strong peak in σ1(ω) at ∼2.7  THz. We analyze the overall Drude-like response using a disorder-dependent (unitary scattering) model, then attribute the peak at 2.7 THz to an enhanced density of states at that energy, which is caused by the presence of a van Hove singularity arising from a commensurate twisting of the two graphene layers.
© 2013 +American Physical Society

... The transmission THz spectra of the BLG were measured using a conventional THz-TDS system (TeraView TPS Spectra 3000)... THz TDS has proven to be a very useful noncontact technique to study material properties such as dielectric response, complex conductivity and refractive index in the far-infrared range without the need for Kramers-Kronig analysis ...