Terahertz Time-Domain Spectroscopy

One of the established measurement techniques in the terahertz spectral range is terahertz time domain spectroscopy (TDS). It is based on the generation of broadband electromagnetic radiation by ultrashort femtosecond (fs) laser pulses and on detection with the pump-probe principle. The advantages here are a coherent detection of the terahertz waves and thus a high-resolution amplitude and phase recording of the terahertz electric field in the time domain. This measurement technique suppresses incoherent radiation, i.e. there is no interference from room temperature and ambient light.

Main Applications

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.

Example Projects


Flexible Pipe Inspection

Our measuring system allows direct testing of the pipe wall thickness at four freely selectable positions.


Terahertz Mail Scanner

The use of terahertz mail scanners in the postal logistics chain makes it possible to warn people at risk of letter or parcel bombs in good time without opening the mail items.



A Laser Concept for the Future of Terahertz Measurement Technology.



In the project »SelfPaint«, we are working with the Fraunhofer Institutes IPA and FCC to develop a self-programming paint cell for unit numbers of one.