Revealing the invisible - identifying concealed substances by means of terahertz spectroscopy

Is that powder in the envelope dangerous? Is the right mixture flowing through the pipe? Is the semiconductor doped correctly? Terahertz spectroscopy can help answer these and other critical questions. This article first describes some of the special features of terahertz spectroscopy in relation to substances in their various physical states, and then discusses automated evaluation of the measurements by means of chemometrics.