February 2004

10 Emerging Technologies That Will Change Your World

Continued from page 5

By Technology Review

DON ARNONE
T-Rays

With the human eye responsive to only a narrow slice of the electromagnetic spectrum, people have long sought ways to see beyond the limits of visible light. X-rays illuminate the ghostly shadows of bones, ultraviolet light makes certain chemicals shine, and near-infrared radiation provides night vision. Now researchers are working to open a new part of the spectrum: terahertz radiation, or t-rays. Able to easily penetrate many common materials without the medical risks of x-rays, t-rays promise to transform fields like airport security and medical imaging, revealing not only the shape but also the composition of hidden objects, from explosives to cancers.

In the late 1990s, Don Arnone and his group at Toshiba's research labs in Cambridge, England, were eyeing t-rays as an alternative to dental x-rays. The idea was that t-rays, operating in the deep-infrared region just before wavelengths stretch into microwaves, would be able to spot decay without harmful ionizing radiation. In tests, the researchers fired powerful but extremely short pulses of laser light at a semiconductor chip, producing terahertz radiation (so called because it has frequencies of trillions of waves per second). Passing through gaps or different thicknesses of material changes the rays' flight time, so by measuring how long each t-ray took to pass through an extracted tooth and reach a detector, the researchers were able to assemble a 3-D picture of the tooth.