For soldiers in Iraq and Afghanistan, the most dangerous threat comes not in the form of a bullet, but a bomb. According to NATO, improvised explosive devices (IEDs for short) account for over half of all deaths among coalition soldiers.
A big part of the problem — especially in Afghanistan — is that the bombs are beyond-tough to spot. They’re made of wood and fertilizer, so metal detectors are close-to-useless. There are sensors that can pick up explosives’ stray molecules, but they have to be right next to the bomb to be effective; the best sensor is still a dog’s nose.
Now, researchers have developed an advanced new bomb detection technique that uses lasers no more powerful than your typical presentation pointer to detect and identify bombs like IEDs from tens, if not hundreds, of feet away.
The technology was developed by a team of researchers at Michigan State University led by chemist Marcos Dantus.
“The laser and the method we’ve developed were originally intended for microscopes,” explains Dantus, “but we were able to adapt and broaden its use to demonstrate its effectiveness for standoff detection of explosives.”
The detection method uses what’s known as a single-beam coherent anti-Stokes Raman scattering technique. Translation? A laser beam like the one pictured up top combines short and long pulses of light to identify individual molecules with a high degree of precision from a safe distance.
Here’s how it works. The laser’s short pulses give the molecules being investigated what the researchers describe as a little “kick,” causing the mystery molecules to vibrate. Every molecule gives off its own unique vibrational frequency in response to the kick from the short pulse.
The long pulses, in turn, listen in on these unique vibrations to identify each molecule with an incredible degree of sensitivity. Just how sensitive are we talking? You can think of each chemical’s short pulse-induced vibration like a fingerprint; according to Dantus, the technique can even tell the difference between chemical isomers — chemicals with the same chemical formula but a different arrangement of atoms.
“Having molecular structure sensitivity is critical for identifying explosives and avoiding unnecessary evacuation of buildings and closing roads due to false alarms,” explans Dantus.
According to Dantus and his colleagues, who have documented the application of the technique in the latest issue of Applied Physics Letters, the bomb-detecting laser technology has already been demonstrated to work from up to 40 feet away, though the researchers estimate that it should work from upwards of 100 yards.
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