Terahertz plasma to detect chemicals

Rensselaer Polytechnic Institute researchers have used a combination of optical, infrared and terahertz radiation to come up with a way to detect chemicals at ranges of up to 20m.

“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, director of the Center for THz Research at Rensselaer.

Zhang is lead author of a paper to be published next week in the journal Nature Photonics. The technique 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 is compared with the material spectrum in the terahertz absorption library.

“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,” said Zhang.

Though most of the research has been conducted in a laboratory setting, the researchers claimed the technology is portable and eventually could be used to check out backpacks or luggage abandoned in an airport for explosives, other dangerous materials or for illegal drugs. On battlefields, it could detect where explosives are hidden.

“I think I can predict that, within a few years, the terahertz science and technology will become more available and ready for industrial and defence-related use,” Zhang claimed.

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