Explosive laser: Shedding light on bombs

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  • Published: Sep 15, 2013
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Explosive laser: Shedding light on bombs

Explosive traces

Standoff explosives trace detection and imaging by selective stimulated Raman scattering. Baggage check photo by David Bradley

A laser that can detect microscopic traces of explosive chemicals on clothing and luggage has been developed by researchers at Michigan State University. The development opens up the possibility of the accurate identification of terror suspects or baggage that may represent a bomb threat at airports and other security checkpoints. Details are published in the latest issue of Applied Physics Letters by MSU's Marshall Bremer and Marcos Dantus.

For many years, scientists have tried to develop lasers that would be powerful enough for analytical applications but safe enough to be used around people, especially outside the protective laboratory environment. The initial inspiration came to Dantus when working in a collaboration with Harvard University where a laser had been developed for detecting cancer but was superficially no more powerful in terms of beam output than a lecturer's laser pointer. “While working on biomedical imaging, I began exploring additional applications,” Dantus says. “We soon learned how effective it was for detecting traces of hazardous substances from distances up to 10 metres away.”

Passenger potential

"Our method uses a single beam and requires no bulky spectrometers," he adds. "It is quite practical and could scan many people and their belongings quickly. The system not only identifies traces of suspicious chemicals but can highlight their precise location in a pocket, on a zip, or elsewhere. The system is unlikely to be developed into a handheld scanner of any kind for use at airport security. Instead, it is more likely to be incorporated into the conveyor systems used for checking luggage and perhaps augment the body scanners that are increasingly common at international airports. The low-power laser - 10 milliwatts - is safe to use on luggage as well as passengers, Dantus says.

Checking the pulse

The technology uses two femtosecond pulses from a single laser, with the second pulse acting as a shadow, reference, wave. The initial resonant pulse is "tuned" to the compounds one wishes to detect, any discrepancy between the two pulses at the detector indicates the presence of those explosive analytes.

“The laser is not affected by the colour or surface of clothes or luggage,” Dantus explains. “The resonant pulse and the shadow pulse are always in balance unless something is detected. Our method has Raman chemical specificity, excellent sensitivity and robust performance on virtually all surfaces.” The team is already in discussions with an aerospace company with the express interest of developing the technology for security applications. Currently, the research is funded by a grant from the US Department of Homeland Security, Science and Technology Directorate. Additional funding would allow a standalone prototype to be built within a year, Dantus hopes. "The next step is to reproduce the characteristics of our laboratory laser setup in a compact laser source. Once that is done the whole system can be designed for field tests," Dantus told SpectroscopyNOW.

Related Links

Appl Phys Lett 2013, 103, 061119: "Standoff explosives trace detection and imaging by selective stimulated Raman scattering"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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