The terahertz range refers to electromagnetic waves with frequencies between 100 GHz and 10 THz, or wavelengths between 3 mm and 30 μm. Light between microwaves and infrared has some unique properties. Terahertz waves can “look inside” plastics and textiles, paper and cardboard. Many biomolecules, proteins, explosives and narcotics also feature characteristic absorption lines – so-called spectral “fingerprints” – at terahertz frequencies. Unlike X-rays, terahertz waves do not have any ionizing effect and are generally considered biologically innocuous.