T-Rays: The Future of Airport Security, the End of Suicide Bombers?

PHOTO Terahertz sensing is said to be promising for medical imaging and the detection of weapons or explosives.

It's the price we pay for living in a post-9/11 world -- waiting on endless lines at airport security, worried about missing a flight, and wondering if all those metal detectors and pat-downs will make us any safer anyhow.

Scientists at Rensselaer Polytechnic Institute in Troy, N.Y., have now made an advance that could substantially change that scenario. Instead of X-rays, try T-rays.

T-rays? Sounds like a dinosaur or something from a high-school cafeteria, but it's really slang for terahertz -- part of the electromagnetic spectrum, like visible light, infrared or ultraviolet -- that could be tremendously useful in remote sensing involved in everything from homeland security to defense to medicine.

The scientists at RPI have now used terahertz sensing to determine the chemical makeup of samples in the lab from up to 67 feet away -- the size of the lab in which they were working -- and say their technology may be effective at considerably greater distances.

Imagine, scientists say, being able to:

Pick out a suicide bomber from a distance -- before he or she can set off any explosives.

Scan the road ahead of a military convoy for hidden explosives.

Shoot images of an enemy satellite 22,000 miles out in orbit, and figure out exactly what it is before it does anything.

"A lot of chemical compounds have chemical signatures in the terahertz range," said Jingle Liu, one of the members of the Rensselaer team, who published their results in the journal Nature Photonics. "We tested hundreds of compounds."

Straight From a Novel

For years, T-rays were the stuff of spy thrillers -- witness this 1996 excerpt from Tom Clancy's "Games of State:"

"He pressed a square, red button on the back of the power pack. 'What you get are terahertz oscillations that wriggle around between the infrared and radio wave area of the spectrum. What that gives you is the ability to tell what's inside or behind something thin -- paper, wood, plastic, almost anything.'"

Terahertz Could Transform Security Scanning

Security agencies are intrigued. Terahertz research is being backed by the Defense Advanced Research Projects Agency (DARPA), the Missile Defense Agency, the Office of Naval Research, and the Departments of Energy and Homeland Security.

"There is stuff you can do with terahertz that you simply can't do with microwaves or optically," said Bruce Carlsten of Los Alamos National Laboratories.

Already, many of the so-called full-body scanners being tried at some airports make use of terahertz, though there are major privacy issues raised by sensors that can see through people's clothes. Many people are concerned about the safety of terahertz radiation, though studies so far seem to suggest that low-level exposure is not harmful.

One good thing about T-rays, scientists say, is that unlike X-rays, they are not ionizing radiation. They do not strip atoms of their electrons, causing the damage that other radiation does.

One bad thing is that while they can detect all sorts of hazards, they also detect almost anything else -- including the water vapor that hangs in the air. It looks like an opaque fog in a terahertz image. The RPI team figured out a way to "see" through vapor, using a low-powered laser.

Engineers elsewhere are experimenting with using them for voice and data transmissions. They can be sent much like a radio transmission, but they can be aimed with precision, and they are very hard for others to intercept.

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