Countering IEDsAir laser will sniff bombs, pollutants from great distance
Princeton University engineers have developed a new laser-sensing technology that may allow soldiers to detect hidden bombs from a distance and scientists better to measure airborne environmental pollutants and greenhouse gases; the new technique differs from previous remote laser-sensing methods in that the returning beam of light is not just a reflection or scattering of the outgoing beam; it is an entirely new laser beam generated by oxygen atoms whose electrons have been “excited” to high energy levels
Princeton University engineers have developed a new laser-sensing technology that may allow soldiers to detect hidden bombs from a distance and scientists better to measure airborne environmental pollutants and greenhouse gases.
“We are able to send a laser pulse out and get another pulse back from the air itself,” said Richard Miles, a professor of mechanical and aerospace engineering at Princeton, the research group leader and co-author on the paper. “The returning beam interacts with the molecules in the air and carries their fingerprints.”
The new technique differs from previous remote laser-sensing methods in that the returning beam of light is not just a reflection or scattering of the outgoing beam. It is an entirely new laser beam generated by oxygen atoms whose electrons have been “excited” to high energy levels. This “air laser” is a much more powerful tool than previously existed for remote measurements of trace amounts of chemicals in the air.
The researchers, whose work is funded by the Office of Naval Research, published their new method 28 January in the journal Science.
Miles collaborated with three other researchers from Princeton’s Department of Mechanical and Aerospace Engineering: Arthur Dogariu, a research scholar and the lead author on the paper, and James Michael, a doctoral student; and Marlan Scully, a lecturer with the rank of professor who also is a professor of physics at Texas A&M University.
The new laser-sensing method uses an ultraviolet laser pulse that is focused on a tiny patch of air, similar to the way a magnifying glass focuses sunlight into a hot spot. Within this hot spot — a cylinder-shaped region just 1 millimeter long — oxygen atoms become “excited” as their electrons get pumped up to high energy levels. When the pulse ends, the electrons fall back down and emit infrared light. Some of this light travels along the length of the excited cylinder region and, as it does so, it stimulates more electrons to fall, amplifying and organizing the light into a coherent laser beam aimed right back at the original laser.
Researchers plan to use a sensor to receive the returning beam and determine what contaminants it encountered on the way back.
“In general, when you want to determine if there are contaminants in the air you need to collect a sample of that air and test it,” Miles said. “But with remote sensing you don’t need to
