Multiphotons sniff out explosives

17 Jun 2002

US firm combats terrorism with a laser technique that detects explosives on passengers boarding airplanes.

Courtesy of Opto & Laser Europe (OLE) magazine

Implant Sciences of the US claims that it has developed a laser-based method of detecting five types of explosive. It says that it has incorporated the technique, which can also detect traces of the drug marijuana, into a battery-powered portable system to screen passengers boarding aircraft.

According to the company, the system can "selectively identify a range of explosives, sound an alarm and print out the concentrations in seconds". Common explosives that have been successfully detected and quantified so far include TNT and C4.

In the wake of last year's terrorist attacks, airport security has become a vital issue. According to Implant Science's estimate, the global explosives-detection market will exceed $1 billion (Euro 1.14 billion) by 2003. The company is clearly confident that its system has potential - it has already set up a dedicated division to manufacture and market it.

Although X-ray scanners are routinely used to bulk-screen airplane passengers and their baggage for explosives, there is a need for more sensitive, portable detection devices that can screen individuals. This was highlighted recently by the case of the alleged "shoe bomber", who was able to board a flight from Paris to Miami with enough explosive hidden in his shoe to have blown a hole in the plane fuselage.

The detection method, developed by Implant Sciences' Leo Krasnobaev, employs resonance-enhanced multiphoton ionization (REMPI) to ionize specific "target" molecules given off by explosives and drugs. REMPI was first pioneered as a technique for isotope enrichment of uranium for use in nuclear power, although it has never been taken up commercially for that application.

The firm says that the REMPI method can detect the presence of explosives down to the parts per trillion level - a success rate some 20-30 times better than that achieved by sniffer dogs.

Company president Anthony Armini said: "Our system is unique in that it uses a laser beam to ionize the vapor from the explosive. We believe that laser ionization is much better for selectively ionizing the explosive molecule than conventional methods using a radioactive source."

Although the firm is reluctant to discuss specific details of the laser system yet, it is believed to be based around a portable, battery-operated ultraviolet source emitting 1 mJ pulses. A prototype is expected later this month and Implant Sciences plans to market the laser as a stand-alone product for use in other applications.