The most important application focus is on time-of-flight measurements, where the time-of-flight of the reflected signals is analyzed. In this way, distances and coating thicknesses can be determined very accurately. This approach underlies the industrially used paint thickness measurement.
Terahertz time-domain spectroscopy is a reliable method for the non-contact and non-destructive characterization of materials, e.g. powders, solids or liquids and gases. Many molecules show characteristic signatures in their absorption spectra in this spectral range – a chemical fingerprint.
Gases show rotational spectra with narrow absorption lines. Only crystalline solids show broad absorption bands due to the phonon vibrations of the crystal. Therefore, powdery or solid substances must have at least a crystalline component to be identified by these absorption bands. Liquids therefore do not show distinct absorption bands. Spectra are evaluated using chemometric methods for reliable substance identification under real operating conditions. The Postscanner is based on the combination of terahertz spectroscopy and chemometric evaluation for the identification of drugs and explosives in mail.
Unlike IR and Raman spectroscopy – which are sensitive to intramolecular vibrational and rotational motions – terahertz spectroscopy provides information on intermolecular motions. Thus, in addition to the mere detection of macromolecules, statements can be made about the state of aggregation, polymorphic structures as well as the crystallinity of the substances.