Terahertz time-domain spectroscopy is used to study properties of nonpolar amorphous materials. Terahertz absorption spectra and refractive indices were measured in a number of glasses, lubricating oils, and polymers, and the results were correlated with material properties.

This paper is a survey of existing and upcoming industrial applications of terahertz technologies, comprising sections on polymers, paint and coatings, pharmaceuticals, electronics, petrochemicals, gas sensing, and paper and wood industries. Finally, an estimate of the market size and growth rates is given, as obtained from a comparison of market reports.

The emission spectra and the lifetimes of the lasing transition ${}^4{I}_{13/2}{-}^4{I}_{15/2}$ in ${\mathrm{Er}}^{3+}$-doped ${\mathrm{TeO}}_2{-\mathrm{Z}\mathrm{n}\mathrm{O}-\mathrm{N}\mathrm{a}}_2\mathrm{O}$ ternary glasses have been studied. The investigation includes two main studies: The first part discusses the Raman spectroscopic analysis of the host glass structure. In the second part, we explain the dependence of ${\mathrm{Er}}^{3+}$-ion photoluminescence near 1500 nm on ${\mathrm{OH}}^{\mathrm{-}}$-ion concentration. The influence of the concentrations of ${\mathrm{Er}}_2{\mathrm{O}}_3$ and the glass structure modifiers (ZnO, ${\mathrm{Na}}_2\mathrm{O})$ on the lifetimes of ${}^4{I}_{13/2}$ level and line shape of the emission spectra has been analyzed. It was observed that the increasing concentrations of ${\mathrm{Er}}^{3+}$ ions resulted in spectral broadening as a consequence of ${\mathrm{Er}}^{3+}$ being distributed in the glass structure. The measured lifetimes of ${}^4{I}_{13/2}$ emission vary between 4.5 and 7.8 ms and strongly depend on OH-ion concentrations. The structural origin of the spectral broadening of the Er emission line is particularly discussed by analyzing the spectral components in the tellurite, modified silicate, and fluoride glass hosts. The number of spectral components at room temperature in Er-doped ${\mathrm{TeO}}_2,$ silicate, and fluoride glasses are compared, and the dependence of line strengths and site-to-site variation of the rare-earth ions on the structure of each glass is also explained. The unusually large broadening of the ${\mathrm{OH}}^{\mathrm{-}}$ band in the ${\mathrm{TeO}}_2$ family of glasses is analyzed in the context of the tellurite glass structure.

Terahertz (THz) time-domain transmission spectroscopy was used to obtain the absorption coefficients and refractive indices of silica, Pyrex, and seven different Schott glasses. The refractive indices were analyzed using the Clausius–Mossotti equation, and the absorption coefficients in terms of the power-law model of far-infrared absorption. Relationships were observed between THz absorption and refractive indices on the one hand, and glass properties on the other. THz transmission data have been shown to provide a useful insight into glass structure.