Laser beams used to detect explosives

Posted by Kate Taylor

Austrian scientists say they've developed a way of using a laser to sniff out explosives from more than 100 meters away.

Vienna University of Technology researchers are using what's known as  Raman-spectroscopy, which involves irradiating a sample with a laser beam. When the light is scattered by the molecules of the sample, it can change the light's wavelength, and thus its colour.

And by analyzing the colour spectrum of the scattered light, it's possible to work out what type of molecules did the scattering.

Until now, samples had to be placed very close to the laser and the light detector for this kind of Raman-spectroscopy.

"Among hundreds of millions of photons, only a few trigger a Raman-scattering process in the sample," says the university's Bernhard Zachhuber.

These scattered particles of light are scattered uniformly in all directions, so that only a tiny fraction travel back to the light detector.

From this very weak signal, though, it's possible to extract enough information using a highly efficient telescope and extremely sensitive light detectors.

The team worked with the Austrian military to test the system with  frequently used explosives, such as TNT, ANFO or RDX. And, says Engelene Chrysostom, "Even at a distance of more than a hundred meters, the substances could be detected reliably."

And the same held true even when the sample was hidden in a nontransparent container. The laser beam is scattered by the container wall, but a small portion of the beam penetrates the box, where it can still excite Raman-scattering processes.

The team expects applications in airport security checks, as well as adacdemic research, for example geological analysis on a Mars mission.