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Laser probe sniffs out landmines

03 Apr 2003

A hand-held optical device that can detect metals, plastics and explosives could speed up the search for landmines.

Researchers from the Technical University of Clausthal in Germany have developed a laser-based device for detecting landmines. The system, which they call a "laser-optical mine detection needle", is hand-held and is said to identify metals, plastics or explosives in real-time.

"The sensor is like a conventional mine detection needle, which looks like a screwdriver, but here we have integrated a microchip laser using fiber-optics," research leader Wolfgang Schade told Optics.org.

The system uses a technique known as laser-induced breakdown spectroscopy (LIBS). It works by firing 0.5 mJ, 1 ns pulses from a miniaturized, passively Q-switched Nd:YAG laser down a fiber-optic cable within the needle. The intense pulses ionize elements within the sample, generating a plasma on its surface.

When the electrons in the plasma recombine they emit light which is then analyzed by the instrument. "The time evolution of the plasma emission for specific wavelengths gives a fingerprint for the material being analyzed," said Schade. He says that traces of cyanide, carbon and explosive materials can be distinguished in this way.

Schade says that this data analysis takes 10 seconds to perform at present. His team is now modifying the microchip laser to speed this up. "The next step is amplification by fiber amplifiers and the use of microchip lasers with a kHz repetition rate instead of the current 200 Hz," he said. "This will mean that the results are all shown after a few seconds."

There are a few other improvements on the cards too. "We also want to apply an 'intelligent' data analysis system that is able to learn," said Schade. "We want to be able to drill a hole and to look at what is behind the hole, whether it is just air or TNT." The team is also hoping to make the device battery-operated.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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