Fraunhofer Institute for Industrial Mathematics ITWMTerahertz time-domain spectroscopy (TDS) has proven to be a reliable method of non-contact and non-destructive characterization of materials such as dry chemicals, solids and liquids. We developed fibre-coupled terahertz measurement systems based on the principle of TDS. By irradiating extended test objects point by point, it is also possible to obtain 2D (imaging) or even 3D (tomography) renderings in addition to the spectroscopic results.
Terahertz waves are electromagnetic waves in the frequency range between 100 GHz and 10 THz. Within this region of the spectrum many molecules exhibit characteristic signatures in their absorption spectra. In addition to this, many substances impermeable to visible light or infrared (IR) are transparent to terahertz waves. The specific interactions of the waves with the matter open up new applications in many fields of measurement technology. Advances in laser and semiconductor technologies during the past years have made it possible to develop suitable sources and detectors for terahertz radiation.
One of the established measurement techniques is terahertz time domain spectroscopy (THz-TDS). It is based on the generation of broad-band electromagnetic radiation by ultra short femtosecond (fs) laser pulses together with the pump-probe principle. The advantages here are coherent detection of the terahertz waves and hence a highly resolved recording of amplitude and phase of the electrical terahertz field in the time domain. This measurement technique suppresses incoherent radiation, i.e. there is no interference due to ambient temperature and light.