Interferometry-aided terahertz time-domain spectroscopy for robust measurements in reflection

Terahertz time-domain spectroscopy systems rely on a correct time base of the acquired signals. In reflection geometry, two sources of optical delays have to be considered: the optical delay line, which enables the sampling principle, and the distance from the emitter and detector to the sample. Both optical paths can be perfectly monitored by using interferometric methods, which leads to a drastic enhancement of the stability and precision of the acquired measurement data. In this contribution we specially focus on the effect of vibrations of the sample or measurement head, which can lead to drastically reduced accuracy of the measurement results when considering layer thickness measurements.