Anharmonicity-driven redshift and broadening of sharp terahertz features of α-glycine single crystal from 20 K to 300 K: Theory and experiment

 Allen, J. L., T. J. Sanders, Josip Horvat, and R. A. Lewis. "Anharmonicity-driven redshift and broadening of sharp terahertz features of α-glycine single crystal from 20 K to 300 K: Theory and experiment." Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 244 (2020): 118635.

Abstract

For the first time, large single crystals of the simplest amino acid, glycine, have been used to determine the temperature dependence of its terahertz spectrum. High-quality spectra with very sharp absorption features are observed at cryogenic temperatures. The α-glycine structure and the purity of the crystals were verified via Raman spectroscopy and X-ray diffraction. Spectral redshift with increasing temperature was observed for all absorption bands in the terahertz region (10–250 cm−1, or 1–8 THz) over the temperature range of 20–300 K. X-ray diffraction revealed expansion in all planes of the crystal lattice over the same temperature range. A Bose-Einstein distribution was used to model the frequency position shift of the two lowest-energy fundamental modes at 50 cm−1 and 69 cm−1. On this basis, we attribute the observed redshift and broadening with increasing temperature to the anharmonic potential associated with the phonon bath.

Terahertz, Infrared, and UV-Vis Spectroscopy Study on Silver@ Polyaniline Core@ Shell Nanocomposites; Optical and Electronic Properties

 Abouelsayed, A., Anis, B., & Eisa, W. H. (2020). Terahertz, Infrared, and UV–Vis Spectroscopy Study on Silver@ Polyaniline Core@ Shell Nanocomposites: Optical and Electronic Properties. The Journal of Physical Chemistry C, 124(33), 18243-18256.

Abstract

We present transmission measurements on silver@polyaniline (Ag@PANI) core@shell nanocomposites over a wide frequency range from terahertz to ultraviolet (0.001–6.2 eV). The Ag@PANI core@shell nanocomposites were prepared using solid-state reaction by mixing aniline sulfate (ANS) with 2.5, 5, 7.5, and 10 wt % AgNO3. The nanocomposites were characterized by transmission electron microscope, ultraviolet/visible spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The optical conductivity σ(ω) was fitted using the localization-modified Drude model together with the Lorentzian function. The incremental loading of AgNO3 leads to an increase in the Drude conductivity (σLMD) and decrease of the scattering rate (γD) due to the increase of electron delocalization of protonated quinoid imine units. In addition, the densities of states NEF at the Fermi level are increased from 1.7 to 2.7 per eV per formula unit, while the conduction bandwidth W is decreased from 0.7 to 0.4 eV with increasing the AgNO3 from 2.5 to 10%. The optically determined band parameters suggest that the addition of AgNO3 modifies the energy state of the Ag@PANI core@shell nanocomposites close to the Fermi energy modifying the half-filled polaron band.

… instrument). Terahertz time domain spectroscopy was used to characterize the Ag@PANI core@shell nanocomposites in the low-frequency range (2-100 cm−1) using a commercial THz- TDS system (TPS spectra 3000 system …

for full paper https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.0c05895

Pulsed THz imaging for thickness characterization of plastic sheets

 Zhai, Min, Alexandre Locquet, and D. S. Citrin. "Pulsed THz imaging for thickness characterization of plastic sheets." NDT & E International 116 (2020): 102338.

Abstract

The thickness of 2, 4, 6, 8, 10, and 12 mm thick polycarbonate (PC) and poly-methyl methacrylate (PMMA) sheets were characterized nondestructively by terahertz time-of-flight tomography in reflection. Due to terahertz attenuation and dispersion in the material, first characterized in transmission, features in the reflected signal associated with structure deep in the sample (i.e., the back interface) may be difficult to identify, and therefore signal processing is employed, namely frequency-wavelet domain deconvolution and a cross-correlation approach in which we account for dispersion. The refractive indices are found to be 

$n\left(\nu \right)=1.67-0.0096v$

for PC and 

$n\left(\nu \right)=1.61-0.0085v$

for PMMA, while the absorption coefficients, which follow the form of the universal dielectric response, are 

$\alpha \left(\nu \right)=0.564+9.075v^{1.669}$

 for PC and 

$\alpha \left(\nu \right)=0.0406+13.66v^{1.776}$

 for PMMA, where ν is measured in THz and the absorption coefficient is in units of cm−1. We show that straightforward analysis techniques that neglect dispersion are limited to measuring layer thicknesses in these materials of less than ~17 mm, while accounting for dispersion results in a factor-of-two improvement, allowing us to measure samples as thick as ~36 mm.

for full paper  and the missing lines see 

https://www.sciencedirect.com/science/article/abs/pii/S0963869519305079

… Tensile strength, ISO 527-2, 60 MPa, 65 MPa. Elongation at break, ISO 527-2, 6%, 4%. THz reflection and transmission spectra were measured with a Teraview TPS Spectra 3000, a broadband THz time-domain system, shown schematically in Fig …

Hydration Shells of DPPC Liposomes from the Point of View of Terahertz Time-Domain Spectroscopy

 Penkov, Nikita V., Valery A. Yashin, and Konstantin N. Belosludtsev. "Hydration Shells of DPPC Liposomes from the Point of View of Terahertz Time-Domain Spectroscopy." Applied Spectroscopy (2020): 0003702820949285.

Abstract

Analysis of structural and dynamic properties of water in suspensions of liposomes composed from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) in three phase states (gel, rippled gel, liquid crystalline phase) by means of terahertz time-domain spectroscopy in 0.3–3.3 THz range was conducted in the current work. Fraction of free water molecules in DPPC liposome suspension was shown to decrease with temperature (compared to the analogous aqueous solution without liposomes), and intermolecular water binding was enhanced. The most crucial changes occur during gel-rippled gel phase transition (pretransition): at temperatures below pretransition point, liposomes alleviate water binding degree, while at temperatures above the transition point, they enhance water binding. This study has demonstrated the high information content of the terahertz time-domain spectroscopy method for exploring the hydration properties of phospholipids in water.

… spectra and refractive index spectra of the substance under investigation were measured at the same time with the help of a TPS Spectra 3000 spectrometer (Teraview, UK) in the range of wavenumber 10–110 cm –1 with the … 

Effect of particle size and deformation behaviour on water ingress into tablets

Skelbæk-Pedersen, Anne Linnet, Mohammed Al-Sharabi, Thomas Kvistgaard Vilhelmsen, Jukka Rantanen, and J. Axel Zeitler. "Effect of particle size and deformation behaviour on water ingress into tablets." International Journal of Pharmaceutics 587 (2020): 119645.

Abstract

Drug release performance of tablets is often highly dependent on disintegration, and water ingress is typically the rate-limiting step of the disintegration process. Water ingress into tablets is known to be highly influenced by the microstructure of the tablet, particularly tablet porosity. Initial particle size distribution of the formulation and the predominant powder deformation behaviour during compression are expected to impact such microstructure, making both factors important to investigate in relation to water ingress into tablets. Two size fractions (<125 and 355–500 µm) of plastically deforming microcrystalline cellulose (MCC) and fragmenting di-calcium phosphate (DCP) were compressed into tablets with porosities ranging from 5 to 30% (with 5% increments). The total porosity of the tablets was measured using terahertz time-domain spectroscopy and liquid transport into these tablets was quantified using a flow cell coupled to terahertz pulsed imaging. It was found that tablets compressed from large MCC particles resulted in slower water ingress compared to tablets prepared from small MCC particles. In contrast, no difference in liquid transport kinetics was observed for tablets prepared across both size fractions of DCP particles. These results highlight the complex interplay between material characteristics, the process induced microstructure, and the liquid transport process that ultimately determines the drug release performance of the tablets.

… Terahertz time-domain spectroscopy (THz-TDS) measurements were acquired in a transmission setup using a Terapulse 4000 spectrometer (Teraview Ltd., Cambridge, UK) (n = 3). The chamber was purged with dry nitrogen gas …

For full paper see https://www.sciencedirect.com/science/article/abs/pii/S0378517320306293

Terahertz imaging aids in art restoration

 

TeraView is pleased to announce that it has begun a collaboration with the Russian Museum’s Technology Research Department in St Petersburg, Russia aimed at demonstrating the power and capabilities of terahertz imaging in art restoration. TeraView is the leading supplier of terahertz systems to support a range of applications. Recently, the use of terahertz imaging in art restoration has been demonstrated by different museums and other institutions across the world. In some paintings and other works of art, terahertz imaging is able to detect the sequence and thickness of the different layers of paint, each of which can be imaged separately, effectively producing a 3D image of the artwork. Terahertz imaging can thus help reveal the artist’s technique, as well as authenticate paintings in some instances where the identity of the artist is in question. Additionally, terahertz imaging can assist art conservation and restoration decisions by providing information on cracks, delamination and defects buried below the surface and not visible to the naked eye or readily accessible with other techniques. The full press release is available to view here.

Terahertz Coating thickness analysis

Designed for the coatings industry, the TeraCota sensor can determine the individual thickness of multiple paint layers on both metallic and non-metallic substrates and offers significant benefits over existing techniques.

The sensor is non-contact, suitable for working on curved surfaces and capable of performing horizontal and vertical line scans.

For more information on the TeraCota system visit TeraView's web site at www.teraview.com #terahertz

Optical constants of CuO and ZnO particles in the terahertz frequency range

 Calvo-de la Rosa, Jaume, Alexandre Locquet, Denis Bouscaud, Sophie Berveiller, and D. S. Citrin. "Optical constants of CuO and ZnO particles in the terahertz frequency range." Ceramics International (2020).

Abstract

The optical constants (complex dielectric function) of CuO and ZnO particles in polyethylene pellets are measured by terahertz time-domain spectroscopy. The determination of the dielectric properties of these materials is of interest for energy-storage applications, for instance. Maxwell-Garnett theory is used to extract the contribution to the frequency-dependent optical constants of the oxide powders. The validity of the assumptions of Maxwell-Garnett theory are experimentally verified and self-consistency of the results of the model confirmed. On this basis, experimental complex permittivity values for isotropic CuO and ZnO oxide powders are reported in the 100 GHz-3 THz range.

for full paper see https://www.sciencedirect.com/science/article/pii/S0272884220318502

"THz transmission data through the pellets were obtained using a TeraView TPS Spectra 3000 in transmission mode. The experimental bandwidth (power spectrum of "

Terahertz Time-of-Flight Tomography Beyond the Axial Resolution Limit: Autoregressive Spectral Estimation Based on the Modified Covariance Method

Zhai, Min, Alexandre Locquet, Cyrielle Roquelet, and D. S. Citrin. "Terahertz Time-of-Flight Tomography Beyond the Axial Resolution Limit: Autoregressive Spectral Estimation Based on the Modified Covariance Method." Journal of Infrared, Millimeter, and Terahertz Waves (2020): 1-14.

Abstract

We present a time-of-flight tomography method for exceeding the naïve axial (i.e., depth) resolution limit of terahertz (THz) deconvolution by autoregressive spectral extrapolation (AR) based on the modified covariance method (AR/MCM). In contrast to Wiener filtering combined with wavelet denoising, AR/MCM does not discard any frequency components in the low signal-to-noise (SNR) regions of the measured data, and unlike the AR approach based on the Burg method (AR/BM), no peak splitting (single peaks in the impulse response function appearing as double peaks) as well as frequency bias (spectral peaks shifted with respect to their correct positions) is observed after deconvolution. After verifying the advantages of AR/MCM over Wiener filtering in conjunction with wavelet denoising as well as over AR/BM, using synthetic data, AR/MCM is employed to reconstruct a single layer of mill scale on a steel coupon from experimental THz time-of-flight tomography data. The reconstruction shows good agreement with the film thickness obtained from destructive cross-sectional measurements. In addition, unlike AR/BM, optimizing the parameters to obtain stable reconstruction is straightforward relying of Akaike’s information criterion suggesting that AR/MCM can be an easier to implement for THz nondestructive characterization of stratigraphy under noisy conditions, particularly when estimates of the stratigraphy may not a priori be available.

Full paper can be found at https://link.springer.com/article/10.1007/s10762-020-00722-1

… that minimizes the AIC. Experiment. The measurement in this work is carried out using a pulsed, broadband THz time domain system from TeraView Ltd. (TPSSpectra 3000), shown schematically in Fig. 1. The GaAs photoconductive …

High performance of talented copper/magneso-zinc titanate nanostructures as biocidal agents for inactivation of pathogens during wastewater disinfection

Nahrawy, Amany M. El, Ahmed M. Bakr, Ali B. Abou Hammad, and Bahaa A. Hemdan. "High performance of talented copper/magneso-zinc titanate nanostructures as biocidal agents for inactivation of pathogens during wastewater disinfection." Applied Nanoscience: 1-17.

Abstract

In the present research, the performance of MZT nano-titanate was established by combining (0.3–0.5) copper nanoparticles (0–0.5C-MZT) to improve the antimicrobial efficacy of promising engineered nanomaterials. XRD characterized the phase purity confirms the formation of magneto-zinc and copper titanates at 750 °C. The morphological features of four engineering nanoceramics were accurately described. As well, the inactivation effects of microbial growth were also evaluated for these kinds of engineered nanomaterials. After that, the disinfection of estimating four harmful waterborne bacteria in real wastewater was appraised. The results obtained of Raman active modes and FT-IR exhibit that the crystallization was strengthened by Cu doping. The natural THz response of the samples appears a distinct attenuation in the THz transmission. In addition, the results showed that 0.5C-MZT is a powerful antimicrobial agent for damaging the targeted pathogens. The results of toxicological safety tests indicated that the nanomaterials examined are safe for environmental applications. The results achieved reveal that the examined proficient dosage (200 mg/L) of studied 0.5C-MZT nanomaterials was practiced to deactivate four predominant waterborne pathogens in wastewater. Eventually, MZT could serve as a smart nano-weapon towards numerous sorts of dangerous pathogenic microbes and results; therefore, recommend that MZT can be employed as a talented disinfecting agent within wastewater processing.

for full paper see https://link.springer.com/article/10.1007%2Fs13204-020-01454-3

… Standard transmission THz/TDS coordination is occupied for measurements using the TPS spectra 3000 system (Teraview Ltd. England) model by using the transmission unit of polyethylene pelts and under Nitrogen gas (N2) purging …

Utilizing multilayer structures to enhance terahertz characterization of thin films ranging from aqueous solutions to histology slides

Sun, Qiushuo, Kai Liu, Xuequan Chen, Xudong Liu, A. I. Hernandez-Serrano, and Emma Pickwell-MacPherson. "Utilizing multilayer structures to enhance terahertz characterization of thin films ranging from aqueous solutions to histology slides." Optics letters 44, no. 9 (2019): 2149-2152.

Abstract

We propose a multilayer geometry to characterize thin-film samples in reflection terahertz time domain spectroscopy. Theory indicates that this geometry has higher sensitivity compared to ordinary transmission or reflection geometries when characterizing both low- and high-absorption samples. Pure water and water–ethanol mixtures are measured to verify the characterization accuracy of the proposed geometry and its capability to measure trace liquids. Paraffin-embedded oral cancer tissue is imaged to further show how the proposed geometry enhances the sensitivity for solid low-absorptive films.

for full paper see https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-9-2149

"The TF liquid measurements were conducted using the Terapulse 4000 from Teraview Ltd. The ethanol (≥99.8%) was from SIGMA-ALDRICH CO. The dove prism was made of fused quartz with a top angle of 38°. The top medium in the liquid measurements was a 2mm-thick fused quartz substrate. 25 µm Teflon spacers were sandwiched in the middle between the quartz prism and the substrate. The incident wave was p-polarized"

2020 OSA Awards and Medals

The OSA has awarded the William F. Meggers Award for recognition of his outstanding work in spectroscopy to Tony F. Heinz

Stanford University and SLAC National Accelerator Laboratory, USA 

For seminal studies of the properties and dynamics of surfaces, interfaces, and nanoscale materials by diverse spectroscopic techniques, including through the development of powerful new methods .

Tony Heinz received a B.S. in physics from Stanford University, USA, and a Ph.D. in physics from the University of California, Berkeley, USA. He is a professor of applied physics and photon science at Stanford University and the Associate Laboratory Director for Energy Sciences at SLAC National Accelerator Laboratory. Previously, he was a research staff member at the IBM Watson Research Center, USA, and a professor of physics and electrical engineering at Columbia University, USA. He is a Fellow of OSA and served as OSA President in 2012. Heinz has developed a wide range of spectroscopic techniques to examine the properties and dynamics of nanoscale systems. These methods include interface sensitive nonlinear spectroscopy and time-resolved approaches, such as terahertz time-domain techniques. The measurement techniques have been applied to elucidate the electronic, optical and chemical properties of 0-, 1-, and 2-dimensional materials and interfaces.  The research  would not have been possible without the insight and hard work of more than 70 graduate students and postdocs over the years.

Influence of SiO2 nanoparticles on morphology, optical, and conductivity properties of Poly (ethylene oxide)

Hameed, Talaat A., F. Mohamed, A. M. Abdelghany, and G. Turky. "Influence of SiO."

Abstract

In this work, a detailed insight to the microstructure, morphology, surface topography, electrical and optical properties in visible and terahertz range was presented for polyethylene oxide (PEO)/silicon dioxide SiO2 nanocomposites. PEO-filled with various contents of SiO2 nanoparticles were synthesized via the solution cast technique. The polycrystalline nature of PEO/SiO2 films was affirmed by the selected area electron diffraction pattern (SAED) recorded by HRTEM measurement and it was found to nearly conformable with X-ray diffraction data. The energy-dispersive X-ray analysis (EDAX) proved the existence of SiO2 with wt% ranged from 0 to 5% as starting fillers. The high-resolution scanning electron microscope planar images indicated uniform distribution of SiO2 nanoparticles within the PEO films. The atomic force microscope 3D images depicted the surface changed from rough to smooth upon the filling with SiO2. The composite samples exhibit absorption spectra that extended from UV–Vis to near infrared regions. Based on Tauc's formula, it was found that the absorption edge shifted from 4.90 to 3.20 eV as the filler fraction increased from 0 to 5 wt%. The analysis of reflective index in the UV–Vis–NIR regions displayed decrement with increasing filler content. Moreover, the refractive index in Vis–NIR regions is good extension to that in THz region expressing the optical quality of studied films. The optical dispersion parameters were analyzed in the view of Wemple-Didomenico single oscillator and Sellmeier model. The values of nonlinear optical parameters (nonlinear susceptibility χ(3) and nonlinear refractive index (n2) were influenced by the filler fractions. Upon the rise of filler content, the conductivity values show slightly decrement.

for full paper see https://link.springer.com/article/10.1007%2Fs10854-020-03591-5

Monitoring the role of enantiomers in the surface modification and adsorption process of polymers imprinted by chiral molecules: theory and practice

Woźnica, Marcin, Monika Sobiech, Norbert Pałka, and Piotr Luliński. "Monitoring the role of enantiomers in the surface modification and adsorption process of polymers imprinted by chiral molecules: theory and practice." Journal of Materials Science: 1-17.

ABSTRACT 

The objective of this study was to explore the role of enantiomers in the surface modification and adsorption process of polymers imprinted by chiral molecules. Here, R-, S- and R/S-1-aminoindanes (TR, TS and TR/S) were used as the model template molecules. Optimization of synthetic protocols facilitated preselection of the most efficient composition for a molecularly imprinted polymer (MIP)— methacrylic acid-co-ethylene glycol dimethacrylate—with satisfactory specificity and an imprinting factor equal to 3. This polymer composition was used further to analyse the effect of configuration of the template on adsorption properties. The results showed preferable adsorption of R-enantiomer, TR in the R-MIP and S-enantiomer, TS in the S-MIP but revealed variations in the binding capacities of TR and TS in the R- and S-cavity (stereoselectivity factor; k = 1.66 to 1.22, respectively). The theoretically analysed binding energies (DEB) of both TR and TS in the R-cavity (DEB = - 506.14 to - 256.77 kcal mol-1 ) and S-cavity (DEB = - 302.42 to - 347.18 kcal mol-1 ) were in agreement with empirical data. Morphology and porosity analyses revealed the impact of the template molecule on the pore system of the MIP and control (a non-imprinted polymer), but enantiomers were only found to have a negligible role. Binding characterization revealed that the physisorption-governed adsorption process and Dubinin– Radushkevich model fitted the experimental data best. Finally, terahertz spectroscopy was employed to confirm the similarity between both materials imprinted by each enantiomer.

for full paper see https://link.springer.com/content/pdf/10.1007/s10853-020-04796-z.pdf

… Terahertz spectroscopy was performed at the Military University of Technology Institute

of Opto- electronics, Warsaw, Poland. A TDS-based spec- trometer was used for terahertz

measurements (Teraview TPS Spectra 300, Cambridge, UK) in transmission …

Simultaneous Investigation of the Liquid Transport and Swelling Performance during Tablet Disintegration

Al-Sharabi, Mohammed, Daniel Markl, Theona Mudley, Prince Bawuah, Anssi-Pekka Karttunen, Cathy Ridgway, Patrick Gane et al. "Simultaneous Investigation of the Liquid Transport and Swelling Performance during Tablet Disintegration." International Journal of Pharmaceutics (2020): 119380.

Abstract

Fast disintegrating tablets have commonly been used for fast oral drug delivery to patients with swallowing difficulties. The different characteristics of the pore structure of such formulations influence the liquid transport through the tablet and hence affect the disintegration time and the release of the drug in the body. In this work, terahertz time-domain spectroscopy and terahertz pulsed imaging were used as promising analytical techniques to quantitatively analyse the impact of the structural properties on the liquid uptake and swelling rates upon contact with the dissolution medium. Both the impact of porosity and formulation were investigated for theophylline and paracetamol based tablets. The drug substances were either formulated with functionalised calcium carbonate (FCC) with porosities of 45% and 60% or with microcrystalline cellulose (MCC) with porosities of 10% and 25%. The terahertz results reveal that the rate of liquid uptake is clearly influenced by the porosity of the tablets with a faster liquid transport observed for tablets with higher porosity, indicating that the samples exhibit structural similarity in respect to pore connectivity and pore size distribution characteristics in respect to permeability. The swelling of the FCC based tablets is fully controlled by the amount of disintegrant, whereas the liquid uptake is driven by the FCC material and the interparticle pores created during compaction. The MCC based formulations are more complex as the MCC significantly contributes to the overall tablet swelling. An increase in swelling with increasing porosity is observed in these tablets, which indicates that such formulations are performance-limited by their ability to take up liquid. Investigating the effect of the microstructure characteristics on the liquid transport and swelling kinetics is of great importance for reaching the next level of understanding of the drug delivery, and, depending on the surface nature of the pore carrier function, in turn controlling the performance of the drug mainly in respect to dissolution in the body.

for full paper see https://www.sciencedirect.com/science/article/pii/S0378517320303641

"2.3. Terahertz Time-Domain Spectroscopy and Imaging. A commercial terahertz system (TeraPulse 4000, Teraview Ltd., Cambridge, UK) was used to conduct all the terahertz measurements in either transmission or reflection mode."

Terahertz-infrared electrodynamics of swingle-crystalline Ba0. 2Pb0. 8Al1. 2Fe10. 8O19 M-type hexaferrite

Ahmed, Asmaa, Anatoly S. Prokhorov, Vladimir Anzin, Denis Vinnik, Alexander Bush, Boris Gorshunov, and Liudmila Alyabyeva. "Terahertz-infrared electrodynamics of swingle-crystalline Ba0. 2Pb0. 8Al1. 2Fe10. 8O19 M-type hexaferrite." Journal of Alloys and Compounds (2020): 155462.

Abstract

Spectral response of single-crystalline Ba0.2Pb0.8Al1.2Fe10.8O19 synthesized by a modified Czochralski method is investigated using terahertz-infrared spectroscopy. Reflectivity, transmissivity, and complex dielectric permittivity spectra of the compound are studied in the temperature range from 6 to 300 K and in the frequency interval 8-8000 cm−1 for two principle polarizations of the radiation electric field relative to the crystallographic c-axis, namely E||c and E⊥c. The resonance absorption lines observed above 80 cm−1 are assigned to polar lattice vibrations basing on a factor group analysis and a comparison with a dielectric response of isostructural compounds. A set of absorption bands is observed in a range of 8–80 cm−1. To clarify their nature, a model is developed that considers electronic transitions within the fine-structured ground state of four-fold coordinated Fe2+. It is shown that the trigonal distortions of the crystal field lead to lowering of the symmetry of 4f1 and 4e tetrahedral site-positions of Fe2+ and, as a result, to further splitting of the ground state spin-orbital sub-levels. Electro-dipole transitions between the corresponding sub-levels are associated with the absorption lines observed in a low-energy response (at 8-80 cm−1) of the Ba0.2Pb0.8Al1.2Fe10.8O19 compound. The study paves the way for the development of low cost materials with high dielectric permittivity (about 30) at terahertz frequencies that are promising for the manufacture of electronic devices with enhanced characteristics.

for full see https://www.sciencedirect.com/science/article/abs/pii/S0925838820318260

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

Gudkov, V. V., M. N. Sarychev, S. Zherlitsyn, I. V. Zhevstovskikh, N. S. Averkiev, D. A. Vinnik, S. A. Gudkova et al. "Sub-lattice of Jahn-Teller centers in hexaferrite crystal." Scientific Reports 10, no. 1 (2020): 1-15.

Abstract

A novel type of sub-lattice of the Jahn-Teller (JT) centers was arranged in Ti-doped barium hexaferrite BaFe₁₂O₁₉. In the un-doped crystal all iron ions, sitting in five different crystallographic positions, are Fe³⁺ in the high-spin configuration (S = 5/2) and have a non-degenerate ground state. We show that the electron-donor Ti substitution converts the ions to Fe²⁺ predominantly in tetrahedral coordination, resulting in doubly-degenerate states subject to the E⊗eE⊗e problem of the JT effect. The arranged JT complexes, Fe²⁺O₄, their adiabatic potential energy, non-linear and quantum dynamics, have been studied by means of ultrasound and terahertz-infrared spectroscopies. The JT complexes are sensitive to external stress and applied magnetic field. For that reason, the properties of the doped crystal can be controlled by the amount and state of the JT complexes.

for full paper see https://www.nature.com/articles/s41598-020-63915-7

They used a terahertz time-domain spectrometer (Teraview TPS 3000 TDS)

Terahertz-Based Porosity Measurement of Pharmaceutical Tablets: a Tutorial

Bawuah, Prince, Daniel Markl, Daniel Farrell, Mike Evans, Alessia Portieri, Andrew Anderson, Daniel Goodwin, Ralph Lucas, and J. Axel Zeitler. "Terahertz-based porosity measurement of pharmaceutical tablets: a tutorial." Journal of Infrared, Millimeter, and Terahertz Waves (2020): 1-20.

Abstract

Porosity, one of the important quality attributes of pharmaceutical tablets, directly affects the mechanical properties, the mass transport and hence tablet disintegration, dissolution and ultimately the bioavailability of an orally administered drug. The ability to accurately and quickly monitor the porosity of tablets during manufacture or during the manufacturing process will enable a greater assurance of product quality. This tutorial systematically outlines the steps involved in the terahertz-based measurement method that can be used to quantify the porosity of a tablet within seconds in a non-destructive and non-invasive manner. The terahertz-based porosity measurement can be performed using one of the three main methods, which are (i) the zero-porosity approximation (ZPA); (ii) the traditional Bruggeman effective medium approximation (TB-EMA); and (iii) the anisotropic Bruggeman effective medium approximation (AB-EMA). By using a set of batches of flat-faced and biconvex tablets as a case study, the three main methods are compared and contrasted. Overall, frequency-domain signal processing coupled with the AB-EMA method was found to be most suitable approach in terms of accuracy and robustness when predicting the porosity of tablets over a range of complexities and geometries. This tutorial aims to concisely outline all the necessary steps, precautions and unique advantages associated with the terahertz-based porosity measurement method.

for full paper see https://link.springer.com/article/10.1007/s10762-019-00659-0

Review of Terahertz Pulsed Imaging for Pharmaceutical Film Coating Analysis

Alves-Lima, Décio, Jun Song, Xiaoran Li, Alessia Portieri, Yaochun Shen, J. Axel Zeitler, and Hungyen Lin. "Review of Terahertz Pulsed Imaging for Pharmaceutical Film Coating Analysis." Sensors 20, no. 5 (2020): 1441.

Terahertz pulsed imaging (TPI) was introduced approximately fifteen years ago and has attracted a lot of interest in the pharmaceutical industry as a fast, non-destructive modality for quantifying film coatings on pharmaceutical dosage forms. In this topical review, we look back at the use of TPI for analysing pharmaceutical film coatings, highlighting the main contributions made and outlining the key challenges ahead.

for full paper see https://www.mdpi.com/1424-8220/20/5/1441

Nondestructive measurement of mill-scale thickness on steel by terahertz time-of-flight tomography

Zhai, Min, Alexandre Locquet, Cyrielle Roquelet, Patrice Alexandre, Laurence Daheron, and D. S. Citrin. "Nondestructive measurement of mill-scale thickness on steel by terahertz time-of-flight tomography." Surface and Coatings Technology (2020): 125765.

Abstract

We measure in a nondestructive and noncontact fashion the thicknesses of three scale films with thicknesses 28.5 ± 1.4 μm, 13.4± 0.9 μm, and 5.1 ± 0.3 μm on steel substrates employing terahertz time-of-flight tomography combined with advanced signal-processing techniques. Wüstite is the dominant phase in the scale films, though magnetite and hematite are also present. Because wüstite is electrically insulating, the incident terahertz electromagnetic pulses largely penetrate into the scale film; however, the pulses are entirely reflected by the underlying electrically conductive steel substrate. Because the film layers are thin, in some cases optically thin, the distinct pulses reflected at the air/scale and scale/steel interfaces overlap in time and thus are not visually evident in the reflected terahertz signal, necessitating the use of deconvolution techniques to recover the sample structure. We compare the merits of three deconvolution techniques, one unsuccessful (frequency-wavelet domain deconvolution) and two successful (sparse deconvolution and autoregressive extrapolation), to characterize the thicknesses of these scale films.

for full paper see  https://www.sciencedirect.com/science/article/abs/pii/S0257897220304345

ExperimentalThe THz experiments were carried out in an air -conditioned laboratory at 22 o C with humidity < 48 %. Otherwise, the samples were stored in a dry box to retard the transformation of wüstite from transforming into magnetite. The experiments shown here were conducted within the 3 months of sample fabrication to ensure that the scale films were primarily composed of wüstite. The THz reflection measurements are taken on a TeraView TPS Spectra 3000, a pulsed, broadband THz time -domain spectroscopy (TDS) system, shown in Fig. 4. 

Terahertz Imaging and Characterization Protocol for Freshly Excised Breast Cancer Tumor

Vohra, Nagma, Tyler Bowman, Keith Bailey, and Magda El-Shenawee. "Terahertz Imaging and Characterization Protocol for Freshly Excised Breast Cancer Tumors." Journal of Visualized Experiments 158 (2020).

This manuscript presents a protocol to handle, characterize, and image freshly excised human breast tumors using pulsed terahertz imaging and spectroscopy techniques. The protocol involves terahertz transmission mode at normal incidence and terahertz reflection mode at an oblique angle of 30°. The collected experimental data represent time domain pulses of the electric field. The terahertz electric field signal transmitted through a fixed point on the excised tissue is processed, through an analytical model, to extract the refractive index and absorption coefficient of the tissue. Utilizing a stepper motor scanner, the terahertz emitted pulse is reflected from each pixel on the tumor providing a planar image of different tissue regions. The image can be presented in time or frequency domain. Furthermore, the extracted data of the refractive index and absorption coefficient at each pixel are utilized to provide a tomographic terahertz image of the tumor. The protocol demonstrates clear differentiation between cancerous and healthy tissues. On the other hand, not adhering to the protocol can result in noisy or inaccurate images due to the presence of air bubbles and fluid remains on the tumor surface. The protocol provides a method for surgical margins assessment of breast tumors.

for full paper see https://cpb-us-e1.wpmucdn.com/wordpressua.uark.edu/dist/6/250/files/2016/05/jove-protocol-61007-terahertz-imaging-characterization-protocol-for-freshly-excised.pdf

Application of Terahertz Spectroscopy and Imaging in the Diagnosis of Prostate Cancer

Zhang, Ping, Shuncong Zhong, Junxi Zhang, Jian Ding, Zhenxiang Liu, Yi Huang, Ning Zhou, Walter Nsengiyumva, and Tianfu Zhang. "Application of Terahertz Spectroscopy and Imaging in the Diagnosis of Prostate Cancer." Current Optics and Photonics 4, no. 1 (2020): 31-43.

Abstract

The feasibility of the application of terahertz electromagnetic waves in the diagnosis of prostate cancer was examined. Four samples of incomplete cancerous prostatic paraffin-embedded tissues were examined using terahertz spectral imaging (TPI) system and the results obtained by comparing the absorption coefficient and refractive index of prostate tumor, normal prostate tissue and smooth muscle from one of the paraffin tissue masses examined were reported. Three hundred and sixty cases of absorption coefficients from one of the paraffin tissues examined were used as raw data to classify these three tissues using the Principal Component Analysis (PCA) and Least Squares Support Vector Machine (LS-SVM). An excellent classification with an accuracy of 92.22% in the prediction set was achieved. Using the distribution information of THz reflection signal intensity from sample surface and absorption coefficient of the sample, an attempt was made to use the TPI system to identify the boundaries of the different tissues involved (prostate tumors, normal and smooth muscles). The location of three identified regions in the terahertz images (frequency domain slice absorption coefficient imaging, 1.2 THz) were compared with those obtained from the histopathologic examination. The tissue tumor region had a distinctively visible color and could well be distinguished from other tissue regions in terahertz images. Results indicate that a THz spectroscopy imaging system can be efficiently used in conjunction with the proposed advanced computer-based mathematical analysis method to identify tumor regions in the paraffin tissue mass of prostate cancer.

for full paper see https://www.osapublishing.org/copp/abstract.cfm?uri=copp-4-1-31

Terahertz Imaging and Spectroscopy Data Acquisition 

All prostate tissue were tested using a TPI system (TeraPulse 4000, TeraView, Cambridge, England) operating in Reflection Spectrum and Imaging Module (RIM). This module adopts a single-point scanning imaging method. A raster-scanning system that changes the position of the sample through a mobile station in an X-Y plane was used, which allowed the terahertz radiation to pass through the individual points of the sample to be measured. The maximum size of the sample that the system can scan is 20 mm * 20 mm, and the minimum scanning step is 0.1 mm. The axial resolution of our TPI system used is around 30 microns and the maximum lateral resolution is around 250 microns. In this study, the scanning area of the sample was about 15 * 5 mm, the resolution of each point was 0.2 mm, and the diameter of the terahertz spot at the focal point is 0.2 mm

Laser process of transparent conducting surfaces for terahertz bandpass ultrathin metamaterials.

Wang, Qinghua, Bingtao Gao, Fatima Toor, Mark Arnold, and Hongtao Ding. "Laser process of transparent conducting surfaces for terahertz bandpass ultrathin metamaterials." In Laser-based Micro-and Nanoprocessing XIV, vol. 11268, p. 112680H. International Society for Optics and Photonics, 2020.

Abstract

Terahertz (THz) optoelectronics have great potentials in communication, imaging, sensing and security applications. However, the state-of-the-art fabrication processes for THz devices are costly and time-consuming. In this work, we present a novel laser-based metamaterial fabrication (LMF) process for high-throughput fabrication of transparent conducting surfaces on dielectric substrates such as quartz and transparent polymers to achieve tunable THz bandpass filtering characteristics. The LMF process comprises two steps: (1) applying ultrathin-film metal deposition, with a typical thickness of 10 nm, on the dielectric substrate; (2) creating periodic surface pattern with a feature size of ~100 microns on the metal film using nanosecond pulsed laser ablation. Our results demonstrate the LMF-fabricated ultra-thin metal film exhibits newly integrated functionalities: (a) highly conductive with sheet resistance of ~20 Ω/sq; (b) optically transparent with visible transmittance of ~70%; (c) tunable bandpass filtering effect in the THz frequency range; and (d) extraordinary mechanical durability during repeated fatigue bending cycles. The scientific findings from this work will render an economical and scalable manufacturing technique capable of treating large surface area for multi-functional THz metamaterials.

for full paper see https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11268/112680H/Laser-process-of-transparent-conducting-surfaces-for-terahertz-bandpass-ultrathin/10.1117/12.2544054.short

Experimental

… 2.5 THz Transmission Measurement Experimental THz transmission spectra, were generated using THz-Time Domain Spectroscopy (THz-TDS) technique 52,53. A 1000D TeraView spectrometer (TeraView Limited, Cambridge)