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QCL-based sensor network reveals bomb-making

08 Oct 2014

Development at Fraunhofer IAF identifies terror threats from far away.

A network of sensors - including some based on quantum cascade lasers - can detect illicit production of explosives and improvised explosive devices. Traces on doorknobs, in sewage or in the air are detected by the sensors and the data fused in a command center to enable the bomb builder's location to be identified.

The Fraunhofer Institute for Applied Solid State Physics is developing an imaging laser technology, based on QCLs, which will allow a precise localization of the dangerous substances. Last week, the researchers demonstrated their sensor technology at a test site in the south of Sweden.

Nowadays, terrorists are able to manufacture bombs and IEDs with relative ease, requiring few aids and using easily-accessible materials such as synthetic fertilizer. The security forces do not always succeed in preventing the attacks and tracking down illegal workshops in time. However, bomb manufacturing often leaves its tracks: remains of the synthetic fertilizer stick to stairs and doorknobs, waste from the manufacturing process gets into the sewerage system and is deposited in air ducts.

Previously, no technology for systematically identifying illegal bomb production at an early stage has been commercially available. The Fraunhofer researchers have now developed a sensor network as part of the EU project EMPHASIS, which can detect such activity at an early stqge and locate it precisely. Last week, in Sweden, the developers showed how a simple kitchen used to manufacture explosives can be tracked down at the test site of the Swedish Defence Research Agency (FOI) near Grindsjön.

To minimize the number of "false positive" discoveries, different sensor technologies for early and precise localization of illegal bomb manufacturing are involved. The sensors are placed at different appropriate locations in a community - such as on apartment buildings or in sewers. Thus any suspect waste materials produced during the manufacturing of explosives and bombs can be detected early on.

In the command center, the data from all sensors is collected and analyzed automatically. Suspicious results trigger an alarm. With the help of laser-based measurement techniques, security forces can then remotely localize the bomb workshop from a distance. The IAF's infrared laser system in Freiburg evaluates the data from the spectroscopic measurements directly and presents its results on a monitor.

Dr. Frank Fuchs, who leads the project at Fraunhofer IAF, commented, "Our laser technology can detect even faint traces of dangerous substances from about 20 meters away. This reduces the risk of danger for the security forces. The QCLs we have integrated emit in the infrared region so do not pose a danger to the eye.

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Technical specification

The wavelengths between 7.5 and 11 micrometers are well-suited for such sensing: molecules of organic compounds absorb strongly in this region. Target chemical compounds show specific absorption lines in this area. They can thus be exactly determined using these characteristic chemical "fingerprints".

Quantum cascade lasers are finding applications in solving many diverse sensing problems, adds Fuchs. For example, at airports or train stations, laser technology can be implemented to check suspect luggage for explosives. It also promises quick and precise spectroscopic measurements without costly laboratory examinations when controlling food, medicine or drinking water.

Furthermore, sources of pollution can be found more rapidly in factory environments. "Quantum cascade lasers can be used wherever the chemical nature of a surface or its change due to pollution is of interest," added Fuchs. "As our lasers are widely tunable, they can be adapted specifically for different issues and be the basis for highly sensitive sensors in different applications."

About the Author

Matthew Peach is a contributing editor to optics.org.

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