Science Daily – A major breakthrough in remote wave sensing by a team of Rensselaer Polytechnic Institute researchers opens the way for detecting hidden explosives, chemical, biological agents and illegal drugs from a distance of 20 meters.
The new, all-optical system, using terahertz (THz) wave technology, has great potential for homeland security and military uses because it can “see through” clothing and packaging materials and can identify immediately the unique THz “fingerprints” of any hidden materials.”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,” explains Dr. Zhang.
Terahertz wave sensing and imaging have received a great deal of attention because of their significant scientific and technological potential in multidisciplinary fields. However, owing to the challenge of dealing with high ambient moisture absorption, the development of remote open-air broadband terahertz spectroscopy is lagging behind the urgent need for the technology that exists in homeland security and the fields of astronomy and environmental monitoring. The requirement for on-site bias or forward collection of the optical signal in conventional terahertz detection techniques has inevitably prohibited their use in remote sensing. We introduce an ‘all-optical’ technique of broadband terahertz wave detection by coherently manipulating the fluorescence emission from asymmetrically ionized gas plasma interacting with terahertz waves. Owing to the high atmospheric transparency and omnidirectional emission pattern of the fluorescence, this technique can be used to measure terahertz pulses at standoff distances with minimal water vapour absorption and unlimited directionality for optical signal collection. We demonstrate coherent terahertz wave detection at a distance of 10 meters.