Imaging at a distance

Terahertz (THz) radiation, or far-infrared light, is potentially very useful for security applications, as it can penetrate clothing and other materials to provide images of concealed weapons, drugs, or other objects.

However, THz scanners must usually be very close to the objects they are imaging. Doubts have lingered over whether it is possible to use THz waves to image objects that are far away, because water vapour in air absorbs THz radiation so strongly that most of it never reaches the object to be imaged!

But at the upcoming Conference on Lasers and Electro-Optics and the Quantum Electronics and Laser Science (CLEO/QELS) meeting in Baltimore, an MIT-Sandia team will demonstrate the first real-time THz imaging system that can obtain images from 25 metres away.

The technique takes advantage of the fact that there are a few "windows," or frequency ranges, of the terahertz spectrum that do not absorb water very strongly.