Non-Destructive Short Fault Localization in Advanced IC Packages Using Electro Optical Terahertz Pulse Reflectometry

Zee, B., W. Qiu, J. Alton, T. White, M. Igarashi, and D. Sullivan. "Non-Destructive Short Fault Localization in Advanced IC Packages Using Electro Optical Terahertz Pulse Reflectometry." In ISTFA 2019: Proceedings of the 45th International Symposium for Testing and Failure Analysis, p. 9. ASM International, 2019.

We demonstrate how electro optical terahertz pulse reflectometry (EOTPR) can be used in conjunction with a new one-dimensional lump circuit simulation software to quickly and non-destructively isolate faults in advanced IC packages. In the case studies presented, short failures are accurately located in a series of advanced IC package.


full paper can be seen at https://books.google.co.uk/books?hl=en&lr=lang_en&id=tGXIDwAAQBAJ&oi=fnd&pg=PA9&dq=teraview&ots=1ZOHrHkCtl&sig=0YtoqV0FKmNpAexIVy4z3pyy_-4#v=onepage&q=teraview&f=false

Terahertz diffractive structures for compact in-reflection inspection setup

Siemion, A., P. Komorowski, M. Surma, I. Ducin, P. Sobotka, M. Walczakowski, and E. Czerwińska. "Terahertz diffractive structures for compact in-reflection inspection setup." Optics Express 28, no. 1 (2020): 715-723.

Abstract

Two diffractive optical elements are used to create a compact raster THz scanning setup in reflective configuration. The first one focuses the radiation into the small focal spot on the sample, while the second one collects reflected radiation and focuses it on the detector. To assure small size of the setup and large apertures of optical elements, structures work in the off-axis geometry. Thus, the focal spot is formed 100 mm after and 60 mm below the optical axis of the element, which measures 75 mm in diameter. The designed iterative algorithm allows further minimization of these values.

for full paper see https://www.osapublishing.org/DirectPDFAccess/4CCAC4BA-E671-8D40-99D950830DE0A55F_425611/oe-28-1-715.pdf?da=1&id=425611&seq=0&mobile=no

The refractive index for all frequencies in sub-THz range is equal to approximately 1.59 and the absorption coefficient corresponding to the frequency of 520 GHz is equal to 2.39 cm−1 . These measurements have been conducted using Teraview Spectra 3000 spectrometer for the sample of 3D printing material before manufacturing. Manufactured lenses measure 75 mm in diameter and up to 0.98 mm 

Breast Cancer Detection With Low-Dimensional Ordered Orthogonal Projection in Terahertz Imaging

Chavez, Tanny, Nagma Vohra, Jingxian Wu, Keith Bailey, and Magda El-Shenawee. "Breast Cancer Detection with Low-dimension Ordered Orthogonal Projection in Terahertz Imaging." IEEE Transactions on Terahertz Science and Technology (2019).

Abstract:

This article proposes a new dimension reduction algorithm based on low-dimensional ordered orthogonal projection, which is used for cancer detection with terahertz (THz) images of freshly excised human breast cancer tissues. A THz image can be represented by a data cube with each pixel containing a high-dimensional spectrum vector covering several THz frequencies, where each frequency represents a different dimension in the vector. The proposed algorithm projects the high-dimensional spectrum vector of each pixel within the THz image into a low-dimensional subspace that contains the majority of the unique features embedded in the image. The low-dimensional subspace is constructed by sequentially identifying its orthonormal basis vectors, such that each newly chosen basis vector represents the most unique information not contained by existing basis vectors. A multivariate Gaussian mixture model is used to represent the statistical distributions of the low-dimensional feature vectors obtained from the proposed dimension reduction algorithm. The model parameters are iteratively learned by using unsupervised learning methods, such as Markov chain Monte Carlo or expectation maximization, and the results are used to classify the various regions within a tumor sample. Experiment results demonstrate that the proposed method achieves apparent performance improvement in human breast cancer tissue over existing approaches such as one-dimensional Markov chain Monte Carlo. The results confirm that the dimension reduction algorithm presented in this article is a promising technique for breast cancer detection with THz images, and the classification results present a good correlation with respect to the histopathology results of the analyzed samples.

for full paper see https://ieeexplore.ieee.org/abstract/document/8941261

"The reflection measurements were taken by using a TPSSpectra 3000 pulsed THz imaging and spectroscopy system (from TeraView Ltd., U.K.). The diagram of the system is shown in Fig. 2(a). The system uses a Ti:Sapphire laser that produces an 800-nm pulse to excite the THz emitter and the THz receiver. Upon excitation, the THz emitter generates a time-domain THz pulse, as shown in Fig. 2(b). The Fourier transform of the pulse, as shown in Fig. 2(c), demonstrates a power spectrum of pulse ranging from 0.1 to 4 THz. This emitted pulse is made incident on the sample through a set of mirrors, and the reflected pulse from the sample is directed toward the THz receiver [8]. In the reflection mode measurements, both the THz emitter and the detector are offset 30◦ with respect to the normal direction on the sample. To obtain the THz-reflected signal at each pixel on the tissue to produce an image, the scanning stage was set to move in increments of 200-μm step size using a stepper motor"

TeraCota (Terahertz Coating thickness analysis)

TeraCota is a non-contact, multi-layer coating thickness sensor that uses pulsed terahertz light. The operating principles of this sensor are similar to those of pulsed ultrasound, without the need for coupling fluid.

This sensor uses a broadband pulse of terahertz light to illuminate the coated surface from a short distance. The reflected signal contains reflections at the interface of adjacent coating layers, and it is analysed to determine the thickness of each layer.

The automotive paint process is the initial application area to determine the thickness of individual paint layers following baking. For this application, a successful operation has been demonstrated on all types of basecoats encountered: solid, metallic, and pearlescent.

For qualification, the results are compared with the values obtained from standard thickness sensing modalities (optical microscopy, magnetic gauge, and pulse ultrasound). This article also presents the results of initial field trials carried out in a production environment with a demonstrator system, which is the precursor to handheld and robot-mounted production-ready systems.

Exploring the Robustness of Terahertz-Based at-Line Porosity Measurements for Realising a Non-Destructive Dissolution Assay of Tablets during Manufacturing

Bawuah, Prince, Daniel Markl, Daniel Farrell, Mike Evans, Alessia Portieri, Andrew Anderson, Daniel Goodwin, Ralph Lucas, and Axel Zeitler. "Exploring the Robustness of Terahertz-Based at-Line Porosity Measurements for Realising a Non-Destructive Dissolution Assay of Tablets during Manufacturing." In 2019 AIChE Annual Meeting. AIChE, 2019.

INTRODUCTION

To achieve a continuous downstream manufacturing process with in-process quality monitoring and real-time release testing capabilities, different process analytical technologies (PATs) such as laser scattering methods, near infrared (NIR) spectroscopy, and Raman spectroscopy can be deployed to, for example, measure the particle size of raw materials and powder blends as well as to detect the content uniformity of powder blends and tablets. However, the use of the above-mentioned PAT methods to directly measure and quantify the bulk properties of tablets, e.g. porosity, that govern the mass transport processes and mechanical changes in tablets during disintegration and dissolution, are limited. For example, NIR methods to quantify tablet hardness typically probes surface properties only and these measurements are not necessarily..........

For full paper see https://www.aiche.org/conferences/aiche-annual-meeting/2019/proceeding/paper/260f-exploring-robustness-terahertz-based-line-porosity-measurements-realising-non-destructive

"Terahertz time-domain measurements of all the batches were acquired using a TeraPulse 4000 (TeraView Ltd., Cambridge, UK). The porosity was extracted from the measured terahertz effective refractive index using Bruggeman's effective medium theory [1,5]."

Femtosecond Laser Pulse-Induced Structural Modification of Lanthanum Aluminosilicate Glasses: Refractive Indices in Visible Vs. Terahertz Frequency Regions

Dobesh, David Kotaro, S. K. Sundaram, and R. E. Youngman. "Femtosecond Laser Pulse-Induced Structural Modification of Lanthanum Aluminosilicate Glasses: Refractive Indices in Visible Vs. Terahertz Frequency Regions." Journal of Infrared, Millimeter, and Terahertz Waves 41, no. 2 (2020): 171-193.

Abstract

We studied femtosecond laser modifications of lanthanum aluminosilicate (SAL) glasses with 11–23 mol% La2O3 content. Refractive indices of these glasses were measured in the visible and terahertz frequencies and correlated to the change in the glass structure. The role of lanthanum provided a comparison to traditional glass modifiers within the glass network in terms of polarizability and optical basicity for femtosecond laser irradiation modification of the refractive index. 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) was used to identify aluminum speciation within the SAL glasses. We used prism-coupling and terahertz time-domain spectroscopy (THz-TDS) for visible and THz refractive index measurements, respectively. Our results show a linear correlation between refractive index measurements in visible and terahertz frequencies with systematic rare-earth ion inclusions. In addition, our results demonstrate that THz-TDS can be utilized as a means of extending the detectable limits in refractive index measurements of disordered glass structures.

for full paper see https://link.springer.com/article/10.1007/s10762-019-00651-8

2.5 THz-TDS 

Sample thickness was determined using a calibrated OriginCal caliper. A TeraView TPS 3000 (TeraView, Cambridge, UK) was used for THz-TDS measurements. THz spectra were collected from 0 to 3 THz under ambient conditions in transmission mode detection. Initial reference spectra were collected before sample data collection in pure nitrogen. Incident THz radiation energy was produced from a mode-locked Ti:Sapphire laser with a 800 nm central wavelength, pulse duration of 100 fs, and a repetition rate of 80 MHz. The incident THz pulse was divided into both pump and probe beams. .....

Vibrational Response of Felodipine in the THz Domain: Optical and Neutron Spectroscopy Versus Plane-Wave DFT Modeling

Łuczyńska, Katarzyna, Kacper Drużbicki, Tomasz Runka, Norbert Pałka, and Jan Węsicki. "Vibrational Response of Felodipine in the THz Domain: Optical and Neutron Spectroscopy Versus Plane-Wave DFT Modeling." Journal of Infrared, Millimeter, and Terahertz Waves (2019): 1-36.

Abstract

We present a joint experimental and computational terahertz (THz) spectroscopy study of the most stable polymorph (form I) of an antihypertensive pharmaceutical solid, felodipine (FLD). The vibrational response has been analyzed at room temperature by combining optical (THz-TDS, FT-IR, THz-Raman) and neutron (INS) terahertz spectroscopy. With the challenging example of a large and flexible molecular solid, we illustrate the complementarity of the experimental techniques. We show how the results can be understood by employing ab initio modeling and discuss current progress in the field. To this end, we employ plane wave formulation of density functional theory (plane wave DFT) along with harmonic lattice dynamics calculations (HLD) and ab initio molecular dynamics (AIMD) simulations. Based on a comprehensive theoretical analysis, we discover an inconsistency in the commonly accepted structural model, which can be linked to a distinct librational dynamics of the side ester chains. As a result, only a moderate agreement with the experimental spectra can be achieved. We, therefore, propose an alternative structural model, effectively accounting for the influence of the large-amplitude librations and allowing for a comprehensive analysis of the vibrational resonances up to 4.5 THz. In that way, we illustrate the applicability of the computationally supported THz spectroscopy to detect subtle structural issues in molecular solids. While the provided structural model can be treated as a guess, the problem calls for further revision by means of high-resolution crystallography. The problem also draws a need of extending the THz experiments toward low-temperature conditions and single-crystal samples. On the other hand, the studied system emerges as a challenge for the DFT modeling, being extremely sensitive to the level of the theory used and the resulting description of the intermolecular forces. FLD form I can be, hence, considered as a testbed for the use of more sophisticated theoretical approaches, particularly relying on an advanced treatment of the van der Walls forces and going beyond zero-temperature conditions and harmonic approximation.

for full paper see https://link.springer.com/article/10.1007/s10762-019-00634-9

"Standard THz time-domain spectroscopy (THz-TDS) has been used for the determination of the dielectric function. Teraview TPS 3000 unit with accessories in transmission configuration was used. The main parameters of the system are an accessible spectral range of 0.06–3.5 THz, signal to noise greater than 4000:1, and the spectral resolution better than 0.06 THz. The chamber was purged with dry air to eliminate water vapor. FLD was mixed with a high-density polyethylene (HDPE) powder to reduce the attenuation from the sample. The material was ground using a mortar and pestle to reduce the particle size and to avoid the scattering loss. Next, the sample was mixed with the PE matrix powder. The sample was then pressed into a pellet (400 mg weight and 13 mm in diameter), using a hydraulic press. As a reference, a pellet made of pure polyethylene, with the same diameter and the weight of 360 mg, was prepared. The spectrum was acquired by the accumulation of 3600 scans and transformed into the absorption form using a standard, 3-term Blackman-Harris apodization function."

TeraPulse Lx: Future-proof your research with the TeraPulse Lx Modular System

TeraPulse Lx

Future-proof your research with the TeraPulse Lx Modular System

The TeraPulse Lx system is the latest addition to TeraView’s world-leading product family for terahertz analysis. It has been designed to meet the needs of the researcher in imaging or spectroscopy applications.

The system’s modular architecture gives the user both flexibility and expandability and is compatible with TeraView’s extensive and unique Terahertz Toolbox range of accessories. For the first time, these robust fibre-connected modules are available as user exchangeable plug and play devices. All systems include the TeraView patented laser-gated photoconductive emitters and detectors. The new TeraPulse Lx sample chamber has optical fibre coupling throughout, for unprecedented stability
and portability.

The lightweight compact core unit allows for easy transport between locations, and is available in both table-top and 19” rack-compatible formats. The system boasts an industry-leading 3,200 ps time-delay line, as standard.

see www.teraview.com  for more information

Terahertz-infrared spectroscopy of Ti4+-doped M-type barium hexaferrite

Alyabyeva, Liudmila, Samvel Yegiyan, Victor Torgashev, Anatoly S. Prokhorov, Denis Vinnik, Svetlana Gudkova, Dmitry Zherebtsov, Martin Dressel, and Boris Gorshunov. "Terahertz-infrared spectroscopy of Ti4+-doped M-type barium hexaferrite." Journal of Alloys and Compounds 820 (2020): 153398.

Abstract

We report on the first detailed investigations of the terahertz-infrared dielectric response of potential multiferroic single crystalline Ti-doped M-type barium hexagonal ferrite, BaFe12-xTixO19, with concentrations of the dopant above (x = 1.15) and below (x = 0.62) the critical concentration that corresponds to changes of the charge compensation mechanism. Employing terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy, we performed measurements of the spectra of complex dielectric permittivity ε*(ν) = ε′(ν)+iε"(ν) at frequencies ν = 2-8000 cm−1 (0.06–240 THz) and in the temperature interval T = 10–300 K. The effect of aliovalent cation substitution on the low-energy response of barium hexaferrite is analyzed and discussed. A rich set of polarization- and temperature-dependent excitations is observed and their origin assigned to the electronic transition within the ground state 5E of the four-fold coordinated divalent iron, to relaxational dynamics of domains, and to phonon resonances.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0925838819346444

"At terahertz frequencies (7- 100 cm-1, resolution 1.2 cm-1), spectra of real and imaginary parts of the complex dielectric permittivity were directly (without using Kramers-Kronig analysis) determined with the help of terahertz time-domain spectrometers TeraView TPS 3000"

Effect of aluminium substitution on low energy electrodynamics of barium-lead M-type hexagonal ferrites

Ahmed, Asmaa, Liudmila Alyabyeva, Victor Torgashev, Anatoly S. Prokhorov, Denis Vinnik, Martin Dressel, and Boris Gorshunov. "Effect of aluminium substitution on low energy electrodynamics of barium-lead M-type hexagonal ferrites." In Journal of Physics: Conference Series, vol. 1389, no. 1, p. 012044. IOP Publishing, 2019.

Abstract 

We present the first detailed study of the terahertz-infrared dielectric response of single crystalline lead-substituted M-type barium hexaferrites doped with Al3+. The broadband spectra of complex dielectric permittivity ε*(ν)=ε'(ν)+iε"(ν) of Ba0.8Pb0.2AlxFe12-xO19 with concentrations of the dopant x(Al)=1.2, 3, 3.3 are obtained for two principle polarizations using Fourier-transform infrared spectroscopy and terahertz time-domain spectroscopy in the temperature range from 4 to 300 K and at frequencies from 10 cm-1 up to 8000 cm-1 . We observe a rich set of excitations and assign them to the electronic transitions within the ground state 5E of the 4-fold coordinated divalent iron and to phonon resonances. Effect of Al3+ cation substitution on low energy (terahertz) dielectric response and infrared phonon spectra of barium-lead M-type hexaferrites is analysed and discussed. 

for full paper see https://iopscience.iop.org/article/10.1088/1742-6596/1389/1/012044/pdf

........TeraView TPS 3000) equipped with exchange gas cryostats were used to obtain the spectra of complex dielectric permittivity in the 10-100 cm-1 frequency range....................

Terahertz-infrared spectroscopy of single crystalline m-type hexaferrite BaTix Fe12-xO19

Yegiyan, S. R., L. N. Alyabyeva, V. I. Torgashev, D. A. Vinnik, S. A. Gudkova, A. S. Prokhorov, M. Dressel, and B. P. Gorshunov. "Terahertz-infrared spectroscopy of single crystalline m-type hexaferrite BaTixFe12-xO19." In Journal of Physics: Conference Series, vol. 1389, no. 1, p. 012038. IOP Publishing, 2019.

Abstract

We have studied polarization-dependent broad-band dielectric response of singlecrystalline Ti-substituted barium hexaferrites BaTixFe12-xO19, x=0.64., 0.75, 1.1, in the frequency range from 10 to 8000 cm-1 and at temperatures from 5 to 300 K. In addition to a rich set of phonon resonances located at frequencies from 90 to 800 cm-1 we observed an unusual low-energy response (terahertz region, 10-100 cm-1 ) stemming from two different effects: relaxational process and second order spin-orbit coupling in Fe2+ ground state, that may set up new prospects for doped hexaferrites in terahertz technologies. 

for full paper see https://iopscience.iop.org/article/10.1088/1742-6596/1389/1/012038/pdf

The measurements of transmission spectra at frequencies from 10 to 100 cm-1 where performed with the help of time-domain spectrometer TeraView TPS Spectra 3000 with spectral resolution 1.2 cm-1 . 

Dual phases of crystalline and electronic structures in the nanocrystalline perovskite CsPbBr3

Whitcher, T. J., L. C. Gomes, D. Zhao, M. Bosman, X. Chi, Y. Wang, A. Carvalho et al. "Dual phases of crystalline and electronic structures in the nanocrystalline perovskite CsPbBr 3." NPG Asia Materials 11, no. 1 (2019): 1-12.

Abstract

Inorganic perovskites have recently attracted much attention as promising new nanocrystalline materials that have interesting fundamental phenomena and great potential in several applications. Herein, we reveal unusual structural and electronic changes in nanocrystalline cesium lead bromide (CsPbBr3) as a function of temperature using high-resolution spectroscopic ellipsometry, high-resolution transmission electron microscopy and terahertz spectroscopy measurements supported by first-principles calculations. New dual phases of crystalline and electronic structures are observed due to the nanocrystalline nature of the material. Interestingly, a change in the electronic structure occurs below 150 K, and the rate at which the nanocrystal transitions from the tetragonal to orthorhombic phase is found to be nonlinear with temperature. Our results show the importance of the charge and lattice interplay in determining the dual phases and fundamental properties of nanocrystalline materials.

for full paper see https://www.nature.com/articles/s41427-019-0170-6

Terahertz spectroscopy

Our THz spectra of the CsPbBr3 perovskite thin film samples were measured using a THz time domain spectrometer (TeraView TPS 3000) Combined with a Janis ST-100-FTIR continuous flow cryostat, a homemade three-axis alignment stage and a Cryo Industries cryo-cooler (20–30 K).

Low temperature sintering of Zn4B6O13 based substrates, their microstructure and dielectric properties up to the THz range

Szwagierczak, D., B. Synkiewicz-Musialska, J. Kulawik, E. Czerwińska, N. Pałka, and P. R. Bajurko. "Low temperature sintering of Zn4B6O13 based substrates, their microstructure and dielectric properties up to the THz range." Journal of Alloys and Compounds 819 (2020): 153025.

Abstract

Tape casting was used to prepare green tapes based on pure and doped Zn4B6O13 ceramics that are destined for LTCC high frequency substrates. In order to broaden the sintering temperature range, three additives which were based on Zn2SiO4–Li2TiO3, AlF3–CaB4O7–Li2TiO3 and Zn2SiO4–MgTiO3, were selected using heating microscope studies. Differential thermal analysis was used to establish the optimal firing profiles. The microstructure and composition of the sintered ceramics were examined by scanning electron microscopy, energy dispersive spectroscopy and the X-ray diffraction method. Owing to the low sintering temperatures and good compatibility with commercial Ag thick films, multilayer substrates based on green tapes made of the developed materials can be cofired at 900–920 °C. The dielectric properties were studied in a broad range up to the THz frequencies. The most advantageous properties for LTCC substrates, such as high densification degree, a low dielectric permittivity (6.9 at 1 THz) and a low dissipation factor (0.005 at 1 THz) were exhibited by the Zn4B6O13 ceramic to which 10% Zn2SiO4 and 5% MgTiO3 were added.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0925838819342719

… The TDS setup (TeraView, UK) uses a complicated optoelectronic system with a femtosecond laser, photoconductive antennas and a delay line to generate and accurately detect about 0.5 ps long electromagnetic pulse …

Optical properties of BiB3O6 in the terahertz range

Li, Yang, Jingguo Huang, Zhiming Huang, Nazar Nikolaev, Grigory Lanskii, Alexander Mamrashev, and Yury Andreev. "Optical properties of BiB3O6 in the terahertz range." Results in Physics 16 (2020): 102815.

Abstract

We present the spectra of the refractive index and the absorption coefficient of BiB3O6 (BIBO) crystal measured by the means of terahertz time-domain spectroscopy in the frequency range of 0.18–2.75 THz. We observe a large birefringence Δn = nZ − nX = 1.5 and the values of absorption coefficients of all three axes to be less than 5 cm−1 in the range below 1 THz. We report weak absorption lines in the vicinity of 2.28 and 2.6 THz for the Z-axis. Our results show that at room temperature BIBO has a lower absorption than other popular oxygen-containing nonlinear crystals: β–BBO, LBO, KTP, and LN. Thus, we assume the crystal to be an efficient THz radiation generator under intense laser pumping.

for full paper see https://www.sciencedirect.com/science/article/pii/S2211379719330189

"The study was carried out at the temperature of ~17 °C in transmission configuration with commercial terahertz time-domain spectrometer TeraPulse 4000 (TeraView, UK). The samples under study were stuck to the 4.8 mm diaphragm placed in the focal plane between elliptical mirrors of the spectrometer. The THz beam waist in the focal plane is about 4 mm for the lowest frequencies. Two wire-grid polarizers were additionally installed in front of the generator and detector correspondingly to increase the polarization contrast of the system since BIBO exhibit large birefringence. "

Monitoring of air voids at plastic-metal interfaces by terahertz radiation

Pałka, Norbert, Andrzej Rybak, Tomasz Jakubowski, Marek Florkowski, Marcin Kowalski, Przemysław Zagrajek, Marek Życzkowski, Wiesław Ciurapiński, Leon Jodłowski, and Michał Walczakowski. "Monitoring of air voids at plastic-metal interfaces by terahertz radiation." Infrared Physics & Technology 104 (2020): 103119.

Abstract

The time domain spectroscopy (TDS) setup in a reflection configuration was exploited for non-destructive measurements of four samples with a 10-mm (approx.) leaf-shaped air void at the interface between the plastic and metal structures. We identified and measured the material parameters of the samples required for precise determination of the voids’ thicknesses in the range of 125–500 μm. For high resolution measurements we selected the reflection TDS setup with a short focal length and developed a method for the accurate calculation of the incidence angle. We used a deconvolution-based method for thickness monitoring of voids and discussed its limitations. The two-dimensional thickness, amplitude and binary maps were exploited for imaging of the void areas. We also showed that the multiplication of the deconvolved and binarised maps can provide relevant information about the real thickness of the layer and the presence of the void in the single image. The correlation coefficient between the real and TDS measured shapes of the leaf in the range 0.8–0.9 suggests a good perspective for this technique in industrial applications.

For full paper see https://www.sciencedirect.com/science/article/pii/S135044951930619X

We determined the refractive index (n) of both the plastic layer and the tape, which are needed for further calculations. The measurements were carried out in the standard TDS system with a transmission configuration using a TPS Spectra 3000 from TeraView. Additionally, we also present the absorption coefficients of the samples, which indicate the transmission properties of the considered material

Terahertz Time-Domain Spectroscopy of Glasses

Sundaram, S. K. "Terahertz Time-Domain Spectroscopy of Glasses." In Springer Handbook of Glass, pp. 909-929. Springer, Cham, 2019.

Abstract

Terahertz-time domain spectroscopy () uses the real and imaginary parts of the dielectric and optical constants for glass characterization over a wide frequency range in the electromagnetic spectrum. This chapter provides an overview and analysis of various THz spectrometers and typical data sets over 0.1−10THz$0.1-10\mathrm{T}\mathrm{H}\mathrm{z}$. Phonon modes in THz region and Lunkenheimer–Loidl plots for disordered materials along with density-functional based tight-binding () modeling results for As2S3$\mathrm{A}{\mathrm{s}}_2{\mathrm{S}}_3$ are described. THz optical and dielectric properties of selected model glass systems, e. g., silica, alkali borate, and silicates, based on works reported in the literature, are discussed. Mixed-alkali effects and thermal stability in terms of THz properties of simple tellurite glass composition, 80TeO2$80\mathrm{T}\mathrm{e}{\mathrm{O}}_2$-10WO3$10\mathrm{W}{\mathrm{O}}_3$-(10−x$10-x$)Li2O$\mathrm{L}{\mathrm{i}}_2\mathrm{O}$-xNa2O$\mathit{x}\mathrm{N}{\mathrm{a}}_2\mathrm{O}$ with x=$x=$ 0, 2, 4, and 6, are reported. Chalcogenide (As-S) glasses show that the refractive indices in THz, infrared, and visible frequencies decrease with arsenic composition up to a point of optimal constrained structure with average coordination number, ⟨r⟩$⟨r⟩$, beyond which the refractive index increases. Our results in hydroxyapatite (Ca10(PO4)6$\mathrm{C}{\mathrm{a}}_{10}(\mathrm{P}{\mathrm{O}}_4{)}_6$⋅$\cdot$(OH)2$(\mathrm{O}\mathrm{H}{)}_2$; HA)-glass (0.05CaO-0.12TiO2$0.12\mathrm{T}\mathrm{i}{\mathrm{O}}_2$-0.17Na2O$0.17\mathrm{N}{\mathrm{a}}_2\mathrm{O}$-0.28ZnO-0.38SiO2$0.38\mathrm{S}\mathrm{i}{\mathrm{O}}_2$) composites demonstrate that the THz-TDS can be a promising non-destructive tool for evaluating these composites and tracking their degradation in simulated body fluids in biological applications.

for full paper see https://link.springer.com/chapter/10.1007/978-3-319-93728-1_26