Laser beam 'kicks' molecules to detect roadside bombs

Soldiers walking after a roadside bomb exploded in the Helmand Province of southern Afghanistan
Image caption Roadside bombs have been one of the leading causes of deaths and injuries in places like Iraq and Afghanistan

A laser beam that makes molecules vibrate could help detect improvised explosive devices, say scientists.

Every molecule vibrates with a unique frequency - so the laser could "sense" bombs while scanning the ground from a safe distance.

The Michigan State University team's work is another attempt to curb the number of deaths from roadside bombs in places such as Afghanistan.

The research appears in the journal Applied Physics Letters.

More than half the deaths of coalition soldiers in Iraq and Afghanistan have been as a result of improvised explosive devices, or IEDs.

The lead developer of the laser sensor, Dr Marcos Dantus, said detecting IEDs had always been a challenge because of the chemical compounds present in the environment that masked the bomb's molecules.

"Having molecular structure sensitivity is critical for identifying explosives and avoiding unnecessary evacuation of buildings and closing roads due to false alarms," he said.

The invention uses a laser beam to probe the chemical composition of an object at a certain distance from the laser.

The beam combines short pulses that "kick" the molecules to make them vibrate with longer pulses.

"The laser and the method we've developed were originally intended for microscopes, but we were able to adapt and broaden its use to demonstrate its effectiveness for standoff detection of explosives," said Dr Dantus.

The researcher said he was not able to describe the technology behind the invention in great detail because of the project's sensitive nature.

"I cannot give you more specific information regarding its implementation," he told BBC News.

"All we are saying is that it could detect explosives from a stand-off distance."

Image caption In 2010, a team of UK scientists developed a "plastic laser" able to sense hidden explosives

Bombs in airports

Many different devices and techniques have been developed to help safely detect roadside bombs.

A UK scientist, Dr Graham Turnbull from University of St Andrews, who has done a lot of research in this area, told the BBC that the latest study was an exciting step forwards for stand-off detection of explosives - despite still being in the exploratory phase.

"The work demonstrates that a laser spectroscopy technique called 'coherent anti-Stokes Raman spectroscopy' can be used for high-sensitivity stand-off detection of explosives," he said.

"The researchers show that their technique is sensitive - they can detect low concentrations of explosives, of a few millionths of a gram per square centimetre, from a distance of one metre.

"They also show that it is highly selective and can even tell apart very similar explosive molecules - this could be important in complex environments like airports where there could be innocent substances that give false positives with other stand-off detection techniques."

Robot dog's nose

In mid-2010, Dr Turnbull and his team developed laser technology able to sense hidden explosives by "pumping" a type of plastic called polyfluorene with photons from another light source.

They found the laser reacted with vapours from explosives such as TNT.

Dr Turnbull suggested placing such a laser on a robotic, perhaps remotely controlled, vehicle that would be able to "sniff around" in a mine field, looking for vapour clouds.

"On a dusty road in Afghanistan there are relatively few things that might give you a false positive and it certainly could have potential in that area," said Dr Turnbull.

"Essentially it's making an artificial nose for a robot dog."

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