Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency[1] (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the ITU-designated band of frequencies from 0.3 to 3 terahertz (THz; 1 THz = 1012 Hz). Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm (or 100 μm). Because terahertz radiation begins at a wavelength of one millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy.
Photon energy in the THz regime is less than the band-gap energy of non-metallic materials and thus THz radiation can penetrate such materials. THz beams transmitted through materials can be used for material characterization, layer inspection, and as an alternative to X-rays for producing high resolution images of the interior of solid objects.[2]
Terahertz radiation occupies a middle ground between microwaves and infrared light waves known as the “terahertz gap”, where technology for its generation and manipulation is in its infancy. It represents the region in the electromagnetic spectrum where the frequency of electromagnetic radiation becomes too high to be measured digitally via electronic counters, so must be measured by proxy using the properties of wavelength and energy. Similarly, the generation and modulation of coherent electromagnetic signals in this frequency range ceases to be possible by the conventional electronic devices used to generate radio waves and microwaves, requiring the development of new devices and techniques.
Here is a research study:
PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 49 (2004) 1595–1607
In vivo study of human skin using pulsed terahertz radiation
Abstract
Studies in terahertz (THz) imaging have revealed a significant difference between skin cancer (basal cell carcinoma) and healthy tissue. Since water has strong absorptions at THz frequencies and tumours tend to have different water content from normal tissue, a likely contrast mechanism is variation in water content. Thus, we have previously devised a finite difference timedomain (FDTD) model which is able to closely simulate the interaction of THz radiation with water. In this work we investigate the interaction of THz radiation with normal human skin on the forearm and palm of the hand in vivo. We conduct the first ever systematic in vivo study of the response of THz radiation to normal skin.