• Frequency range 100 GHz .. 10 THz, wavelengths 3 mm .. 30 µm
• Also known as far-infrared or sub-millimeter waves
• Non-ionizing, but penetrates clothing, paper, cardboard, plastics, …
• Absorbed by water and many organic substances
• High chemical sensitivity

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 radio waves and infrared has some unique properties. Terahertz can “look inside” plastics and textiles, paper and cardboard. Many biomolecules, proteins, explosives or narcotics also feature characteristic absorption lines, so-called spectral “fingerprints”, at frequencies between 0.1 and 5 THz. The two main advantages of terahertz radiation are thus the penetration of conventionally opaque materials on one hand, and a high chemical selectivity on the other hand.

One of the strongest absorbers for terahertz radiation is water, which – depending on the application – turns out to be a blessing or a curse: Air moisture limits the propagation of terahertz rays to a few meters, but vice versa, the characteristic fingerprint enables a high precision in humidity-sensitive measurements. Liquid water is an even more dominant absorber than water vapor. 

Unlike X-rays, terahertz waves do not have any ionizing effects and are generally considered biologically innocuous.