Terrorist
attacks like the attempted Christmas Eve bombing on a Northwest Airlines flight
have led to an increased interest in bomb detection. Researchers at the Rensselaer Polytechnic Institute (RPI) are now using remote
wave sensing to detect hidden explosives, chemical/biological agents, and other
contraband from a distance of 20 meters.
The new
system uses terahertz (THz) radiation, which lies at the far end of the
infrared band of the electromagnetic spectrum, just before the microwave band.
The unique properties of THz waves allow for better detection than traditional
methods, such as X-rays. THz waves can, for example, pass through all
substances except water and metal—from clothing to wood to plastic.
Substances
like explosives emit specific THz “fingerprints.” The new system uses lasers to
detect these waves and compare them to a directory of substances—allowing for
instant identification.
The new system uses lasers to detect the
terahertz radiation that all substances emit. Possible applications include
detecting bombs and drugs in airports and locating explosives on battlefields
(source: Rensselaer Polytechnic Institute/Daria Robbins).
Xi-Cheng
Zhang, Director of the Center for THz Research at RPI, explains the
technology in the university’s press
release:
“We have shown that you can focus an 800 nm laser beam and a 400 nm laser beam
together into the air to remotely create a plasma interacting with the THz
wave, and use the plasma fluorescence to convey the information of the THz wave
back to the local detector.”
Unlike
other detection systems, such as X-rays, THz waves pose little to no health
threat. Because the radiation cannot penetrate water, however, it cannot be
used to detect substances hidden in the body.
Much of
the research has been funded by the U.S. Departments of Homeland Security and
Defense, which are eager for better explosives detection in airports and on
battlefields.
“I think I
can predict that, within a few years, the THz science and technology will
become more available and ready for industrial and defense-related use,” Zhang states.
The
research is detailed in an upcoming paper in Nature Photonics. Co-authors include Rensselaer’s Jingle Liu, Research
Associate Professor Jianming Dai, and Professor See-Leang Chin of Quebec’s University of Laval.
