A new detection method extends the distance from which powerful terahertz technology can remotely sniff out hidden explosives, chemicals and other materials. Benjamin Clough, a doctoral student at Rensselaer Polytechnic Institute, has developed a technique that uses sound waves to boost the effective distance of terahertz spectroscopy from a few feet to several meters. For the innovation, Clough was named winner of the 2011 $30,000 Lemelson-MIT Rensselaer Student Prize, which is awarded annually to a Rensselaer senior or graduate student who has created or improved a product or process, applied a technology in a new way, redesigned a system or demonstrated remarkable inventiveness in other ways. Benjamin Clough, a doctoral student at Rensselaer Polytechnic Institute, has developed a method for extending the distance from which terahertz technology can detect explosives, chemicals and other hazardous materials. Courtesy of Kris Qua, Rensselaer. Clough’s method circumvents a fundamental limitation of remote terahertz spectroscopy, which is that it works at only short distances, so it has not been suitable for detecting bombs or hazardous materials. His method uses sound waves to remotely “listen” to terahertz signals and identify a target. First, two laser beams are focused into the air to create small bursts of plasma, which in turn create terahertz pulses. Second, another pair of lasers is aimed near the target to create a second plasma, which detects the terahertz pulses from the first two laser beams after they have interacted with the material. The detection plasma produces acoustic waves as it ionizes in the air. Using a sensitive microphone to listen to the plasma, Clough detected terahertz wave information embedded in the sound waves. The information was converted into digital data and checked against a library of known terahertz fingerprints to determine the target’s chemical composition. Using acoustics, Clough has identified terahertz fingerprints from several meters away. Separately, he has demonstrated plasma acoustic detection from 11 m, a distance limited only by available lab space.