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Plasmon sensors to put bomb-sniffing canines out of work

Posted: 21 Jul 2014 ?? ?Print Version ?Bookmark and Share

Keywords:plasmon? sensor? bomb?

The ability to increase the sensitivity of optical sensors traditionally had been restricted by the diffraction limit, a limitation in fundamental physics that forces a trade-off between how long and in how small a space the light can be trapped. By coupling electromagnetic waves with surface plasmons, the oscillating electrons found at the surface of metals, researchers were able to squeeze light into nanosized spaces, but sustaining the confined energy was challenging because light tends to dissipate at a metal's surface.

The new device builds upon earlier work in plasmon lasers by Zhang's lab that compensated for this light leakage by using reflectors to bounce the surface plasmons back and forth inside the sensor C similar to the way sound waves are reflected across the room in a whispering gallery C and using the optical gain from the semiconductor to amplify the light energy.

Zhang said the amplified sensor creates a much stronger signal than the passive plasmon sensors currently available, which work by detecting shifts in the wavelength of light. "The difference in intensity is similar to going from a light bulb for a table lamp to a laser pointer," he said. "We create a sharper signal, which makes it easier to detect even smaller changes for tiny traces of explosives in the air."

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The plasmon laser sensor consists of a thin slab of semiconductor separated from the metal surface by a dielectric gap layer. Surface defects on the semiconductor interact with molecules of the explosive DNT. Source: Ren-Min Ma and Sadao Ota, UC Berkeley

The sensor also could be developed into an alarm for unexploded land mines that otherwise are difficult to detect, the researchers said. According to the United Nations, landmines kill 15,000 to 20,000 people every year. Most of the victims are children, women and the elderly.

The U.S. Air Force Office of Scientific Research Multidisciplinary University Research Initiative programme helped support this work. The research's findings were published in online publication of the journal Nature Nanotechnology.


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