The Engineer

07 May 2004 The leading online resource for the engineering industry

From The Engineer, 29 April 2004

Airborne biological warfare agents can be detected at long range by a short burst from a high-powered laser, according to French researchers.

The method could replace the time-consuming process of sending an aircraft to collect air samples and then conducting a lengthybiochemical analysis.

Researchers at the University of Lyon believe their laser could be fired at a suspect cloud, and the emission analysed instantaneously for fluorescent molecules such as riboflavin, a harmless vitamin found in anthrax and other agents. The fluorescence signature of riboflavin would immediately signal the presence of biological warfare agents.

During an experiment in Lyon a water-based aerosol doped with riboflavin was sprayed into the air. A terawatt (one trillion watts) laser was then fired towards the sample in femtosecond bursts and a telescope collected the reflected light and scattered signals. The information from the riboflavin-doped cloud was then compared with that from a pure water aerosol. The fluorescence of riboflavin was clearly detected by the laser.

But the Lyon researchers broke new ground by doubling the wavelength of the light pulses. Instead of one photon from the laser being used to excite the fluorescence in one molecule of riboflavin, two photons were used for each molecule.

Whereas the one-photon method failed to detect fluorescent molecules beyond 2km away, the two-photon method was effective up to 4km from the laser.

Prof Jean-Pierre Wolf of the physics department at the university, who conducted the research, said the detection method will have two phases of development. 'If you see an aircraft which has suddenly released some strange aerosol or exhaust, you can just shoot the laser into the cloud and see instantly if it is biological or not.

This is the first stage, and could be ready to use in two years,' he said. 'The next stage will be to analyse all the air. At the moment it is very difficult because bacteria is everywhere, so we cannot always be sure that something is really a pathogen. This might take 10 years or more to develop,' he said.

Laser laboratory