July 07, 2008 --While bombs get more complicated, identifying them is still pretty simple: someone, or increasingly something, has to get close to it.
Soon bomb squads could safely tell if a suspicious package is an explosive, and from up to 100 meters (328 feet) away, using a laser system developed by researchers at Oak Ridge National Laboratory in Tennessee.
"There are a number of ways to look for explosives," said Oak Ridge National Laboratory researcher Larry Senesac. "But its a lot nicer if you don't have to walk up to a bomb to find out what it is."
Eventually the same technology that could save soldiers from roadside bombs could also spare civilians from food poisoning, say the researchers.
The system is based on on a series of quantum cascade, solid state lasers. Each laser sends out a pulse of light in specific infrared frequencies.
When the lasers hit an object coated with residue from explosives, the light scatters. Some of it bounces back and is picked up by quartz crystals, which act like tuning forks, changing the electromagnetic waves into acoustic waves.
By determining which quartz crystals are activated, and running that specific activation signature through a computer with the chemical signatures of known explosive agents, the system can determine which type of explosive was used.
"This is the first device of its kind," said Charles Van Neste, also of Oak Ridge National Laboratory and the lead author on the paper, which appears in Applied Physics Letters 92.
Other laser-based chemical detection systems exist, but they use powerful lasers that work over a mile away and are dangerous to bystanders.
The new system is so sensitive it can even pick up traces of TNT and other explosives floating in the air. In a different setting, the same system could be programmed pick up signatures associated with spoiled food.
Michael Carpenter, a researcher at the University of Albany, is impressed by both the range of the detection and the selectivity of the system.
"This is a really neat technique," said Carpenter. "What they need to do now is keep pushing the limits of the technology onto more challenging applications."
The range of the experiments has been limited by the distance inside the lab. The researchers expect the system can scan up to 100 meters (328 feet), which they will soon test.
That's far enough that a car can drive at a normal speed while front-mounted lasers sensors scan for roadside bombs and alert the driver, say the researchers. A car-mounted system could happen in as little as a couple of years.
The system will continue to shrink physically while expanding capability. The lasers, which are eye-safe, since they only use about five milliwatts of power, can be easily mass produced and the researchers expect the price will continue to drop.
"I remember the first CD player I bought was over $100," said Senesac. "Today you can buy a CD laser for probably four or five bucks. We expect something similar to happen."
Eventually the researchers envision the system becoming so cheap and small that consumers could find one on their cell phone and use it to scan fruit for freshness.
"We could be coming to a point very much like laser pointers, where you go to Wal-Mart and just pick up some quantum cascade lasers," said Van Neste.
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