Hidden explosives, chemical weapons, biological agents and illegal drugs could one day be optically detectable from up to 20 meters away. How? Well, every substance has its own unique terahertz (THz) radiation “fingerprint”, the waves of which pass through anything other than metal or liquid. Scientists from New York state’s Rensselaer Polytechnic Institute are working on a way of analyzing those waves, then determining what substance they’re emanating from. The process would be harmless to both the subject and the observer, and could make the world a much safer place.

In the past, THz wave analysis has been hampered by the presence of water vapor in the air. The Rensselaer team have gotten around this problem by using laser-induced fluorescence. This process involves focusing two laser beams together into the air, where they create a plasma that fluoresces with THz waves. The nature of that fluorescence contains information regarding the makeup of the source substance, which can be compared to a digital THz library, resulting in an on-the-spot identification of the target material... even if the material itself is hidden from view.

While the technology is still lab-based, the team sees it becoming portable, and being used to check out abandoned luggage at airports, to search for hidden explosives on battlefields, or even to assess chemical spills from a safe distance. One thing it can not do, at this point, is detect substances hidden within body cavities. It definitely, however, still holds a lot of promise.

“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 Xi-Cheng Zhang, director of the Center for THz Research at Rensselaer.

Much of the research funding has come from Homeland Security and the US Defense Department. The team’s findings were recently published in the journal Nature Photonics.