Terahertz Time-Domain Spectroscopy of Glasses

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 \(0.1{-}10\,{\mathrm{THz}}\). Phonon modes in THz region and Lunkenheimer–Loidl plots for disordered materials along with density-functional based tight-binding () modeling results for \(\mathrm{As_{2}S_{3}}\) 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, \(\mathrm{80TeO_{2}}\)-\(\mathrm{10WO_{3}}\)-(\(10{-}x\))\(\mathrm{Li_{2}O}\)-\(\mathrm{\mathit{x}Na_{2}O}\) with \(x=\) 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, \(\langle r\rangle\), beyond which the refractive index increases. Our results in hydroxyapatite (\(\mathrm{Ca_{10}(PO_{4})_{6}}\)\(\cdot\)\(\mathrm{(OH)_{2}}\); HA)-glass (0.05CaO-\(\mathrm{0.12TiO_{2}}\)-\(\mathrm{0.17Na_{2}O}\)-0.28ZnO-\(\mathrm{0.38SiO_{2}}\)) 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.