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Terahertz (THz) properties of seventeen types of wood typically growing within the European area are investigated. The samples include both coniferous and deciduous timbers. The determined properties can be useful for further THz studies on samples consisting completely or partially of wood, for example, art objects. Especially in the field of art conservation, THz spectroscopy is an excellent non-destructive evaluation method, which shows considerable analysis potential.

Using terahertz time-domain spectroscopy (THz-TDS), we monitor the isothermal crystallization kinetics of amorphous polyethylene terephthalate (PET-A). PET-A was tempered at different temperatures and for a varied amount of time to induce a isothermal crystallization. Afterwards the THz spectra were recorded and analyzed. An adapted Avrami equation was used to analyze the spectral data to monitor the isothermal crystallization. It was found that the adapted Avrami theory is a good approach to describe the kinetics of isothermal crystallization and allows to determine kinetic parameters as with classical technologies. Therefore, we conclude that THz-TDS offers a non-destructive method to characterize the kinetics of isothermal crystallization in polymers.

We determined the THz properties of 12 different adhesives which are mainly used for industrial purposes. The adhesives applied can be classified according to their chemical structure: epoxy resins, acrylic resins, and polyurethane based materials. This work represents a basis for future studies, which will concentrate on aging effects, including the absorption of water of adhesive joints. Thus, the dielectric properties of the unaged adhesives are investigated and the results of these measurements are described herein.

The different crystallinity states of high density polyethylene (PE-HD) are investigated using THz time-domain spectroscopy by exploiting the complex permittivity at a frequency range from 0.5 up to 3.5 THz. We found that samples with different crystallinity can be distinguished by comparing the material specific refractive index (n) or rather the linked complex part of the permittivity (∈ ′ ′). Correlating the calorimetrically determined degrees of crystallinity with the absolute values of the refractive index and the specific absorption peak at 2.18 THz, respectively, suggests in both cases a linear correlation.

We report nondestructive measurements of the properties of two-component epoxy adhesives at THz wavelengths using a reflective time-domain spectroscopy system. We describe a simple method to determine the refractive index, layer thickness, and absorption coefficient using time-domain data applying a Fresnel-equation based approach. The results indicate that the adhesive’s curing process may be monitored using a simple parameter extraction technique based on time-domain measurements for systems featuring small bandwidth, showing good agreement with data obtained with from transmission measurements.