Security with New Wave Remote Sensing

Wednesday, July 14, 2010 @ 07:07 PM gHale

New optical wave sensing technology opens the way for detecting hidden explosives, chemical, biological agents and illegal drugs from 20 meters.
The all-optical system, using terahertz (THz) wave technology, has potential for homeland security and military uses because it can “see through” clothing and packaging materials and can immediately identify the unique THz “fingerprints” of any hidden materials.
Terahertz waves occupy a large segment of the electromagnetic spectrum between the infrared and microwave bands.
“The potential of THz wave remote sensing has been recognized for years, but practical application has been blocked by the fact that ambient moisture interferes with wave transmission,” said Xi-Cheng Zhang, Ph.D., director of the Center for THz Research at Rensselaer Polytechnic Institute in Troy, NY.
The “all optical” technique for remote THz sensing uses laser induced fluorescence, essentially focusing two laser beams together into the air to remotely create a plasma that interacts with a generated THz wave. The plasma fluorescence carries information from a target material to a detector where it instantly compares with material spectrum in the THz “library,” making possible immediate identification of a target material.
“We have shown that you can focus a 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,” Dr. Zhang said.
Because of repeated terrorist threats and the thwarted Christmas Eve bombing attempt aboard a Northwest jet, Homeland Security and the Defense Department increased interest to develop THz remote sensing capabilities.
Because THz radiation transmits through almost anything that is not metal or liquid, the waves can “see” through most materials that might be used to conceal explosives or other dangerous materials, such as packaging, corrugated cardboard, clothing, shoes, backpacks and book bags.
Unlike x-rays, THz radiation poses little or no health threat. However, the technique cannot detect materials concealed in body cavities.
“Our technology would not work for owners of an African diamond mine who are interested in the system to stop workers from smuggling out diamonds by swallowing them,” Dr. Zhang said.
Though most of the research has been in a laboratory setting, the technology is portable and eventually officials could use it to check out backpacks or luggage abandoned in an airport for explosives, other dangerous materials or for illegal drugs. On battlefields, it could detect hidden explosives.
The fact each substance has its own unique THz “fingerprint” will show exactly what compound or compounds are hidden, a capability expected to have multiple important and unexpected uses. In the event of a chemical spill, for instance, remote sensing could identify the composition of the toxic mix. Since sensing is remote, no individuals will enter into a danger zone.
“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,” said Dr. Zhang.

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