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Laser detects distant bombs with 99% accuracy

New laser technology makes it possible to identify explosives, biological agents, and hazardous chemicals from a half mile away.

The lasers travel long distances and identify dangerous materials present within powders that commonly act as carriers for explosive nitrates and lethal biological agents such as anthrax and ricin.

Reported in Nature Communications and the Proceedings of the National Academy of Sciences, the technology involves beaming a high-powered laser onto a powder for an extremely short amount of time—about a trillionth of a second.

When laser light contacts the molecules present within the powder, it experiences a scattering effect that can be analyzed to construct a sort of molecular “fingerprint” that reveals its exact chemical makeup, says Vladislav Yakovlev, professor in the biomedical engineering department at Texas A&M University.

“As part of our research, we identified individual nitrates in powder at a distance of a half kilometer. In a single shot we were able to distinguish those chemicals with 99-percent accuracy, and now we’re working on identification from even greater distances.”

‘Raman effect’

The initial success of the detection technology is due largely in part to the fact that researchers can generate an emission that can be detected by a spectrometer that’s positioned more than a half-mile away.

Traditionally, collecting an excited signal from such long distances has been a significant obstacle to developing remote-sensing technology, but by taking advantage of the inherent properties of the targeted powder, researchers have been able to dramatically amplify the resulting emission.

“In very simple terms, we can take a powder, shine a laser on this powder, and we get a type of scattering effect that enhances our signal,” Yakovlev says. “This was the first demonstration that this is indeed possible with powders.”

The powder provides the conditions by which light is amplified. When a laser passes through the powder, its wavelength is not fully absorbed. Instead, some of the light from the laser scatters, and the path length increases because of this multiple scattering—something scientists refer to as the “Raman effect.”

Target from the air

This scattered light is then emitted from the powder in a strong, diffuse form that is visually similar to a bright LED light. It’s this extremely bright emission that can be collected from long distances.

“We get a large amount of energy into the system in a very short amount of time. This is what allows the process to happen,” Yakovlev says. Yakovlev and colleagues have been able to increase the scattering efficiency by nine orders of magnitude, meaning more light can be detected from greater distances.

It’s an achievement that could pave the way for the technology’s use in military and homeland security applications, says Yakovlev.

“Ideally, you’d like to target a suspicious substance from an airplane, possibly, which could beam a laser at the powder and collect the resulting signal with a powerful parabolic antenna so that the signal could then be analyzed while keeping personnel out of harm’s way.”

Marian O. Scully, professor physics and astronomy, and researchers from Moscow State University contributed to the report. The National Science Foundation and the US Air Force Research Laboratory provided funding.

Source: Texas A&M University

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