Bomb-detecting sensors advance at 'terahertz' scale

A dual-laser laboratory device has opened the door to remote detection of smuggled bombs and drugs at 30-foot distances, physicists report.

A Nature Photonics journal study led by Jingle Liu of Rensselaer Polytechnic Institute in Troy N.Y., reports remote sensing success using terahertz frequency spectroscopy, which acts in the submilliter radiation band between microwaves and X-rays. Able to pass through cloth, paper and other materials, such terahertz signals had been defeated by water in the atmosphere, until now.

"The most immediate application is in detecting terrrorists," Liu says. "We think this could be scaled up to work at very long distances."

In the study, Liu and colleagues focused two lasers (one a 400-nanometer laser and the other an 800-nanometer laser) at a distance point to create a wave of fluorescence radiation in the terahertz frequency. This fluorescene reveals the terahertz chemical signatures of the material without being absorbed by atmospheric water vapor. In a blind test, the team detected the bomb ingredient "4A-DNT" at a distance of just over 30 feet away.

"This wouldn't see you naked at the airport," Liu adds. "It would detect substances very efficiently." The study research is partly funded by the Defense Threat Reduction Agency (DTRA).