No, this isn't science fiction.
What it is
A type of electromagnetic radiation in the terahertz range of the electromagnetic spectrum. (about one millimeter of wavelength) This puts them between the infrared and microwave wavelengths.
All matter emits very weak terahertz radiation. The amount and precise frequency varies depending on the chemical element or compound. With an active T-ray source, objects can be "T-rayed", which works like x-rays, but reveals different things. T-rays are potentially capable of analysing the precise composition and structure of objects without doing them any damage. Unlike x-rays, this radiation can't penetrate a human body, but it does go through the clothing a person has on. That's right - people look naked under T-rays. Yes, like those "x-ray specs" of classical boy's fantasy.1 But this isn't fiction, just very exciting science. The potential applications for T-ray emitters and sensors are astounding.
Why it hasn't been here before
Until now, T-rays haven't gotten much attention because both producing and measuring them is very difficult and expensive. But recent advances with using semiconductors for detection promise a great price drop. And just recently (November 2002), a 20-Watt terahertz ray was produced, which is 100'000 times stronger than any T-ray before. Also recently, a T-ray camera small enough to fit on a space probe was developed by the ESA. It won't be all that long now until the first commercial applications.
What it's good for
- Quality Control
T-rays can be used to discern the fat content of meat, determine whether tomatoes are ripe, inspect packaging or check for defects in semiconductors, to name a few. And all these tests are non-destructive, unlike many conventional analysis methods.
The search for water in the Universe has found an excellent tool in this new radiation. Water emits a specific frequency, which can be measured by the new ESA camera.
What it's bad for
Unfortunately, as with most if not all groundbreaking technologies, there is also a dark side. Because of their capability to see through things, T-rays are excellent tools for espionage and general invasion of privacy. This is mainly due to one special application: Using T-rays, letters can be read unopened. (The paper is transparent but the ink isn't.)
(1) However the images aren't in color and of rather low quality. Tough luck, perverts.
Sources: Der Spiegel, #41/2002 (18.11.02), verified on various websites.