Plastic Lasers Sense Explosives
Light output of a blue plastic laser used in the explosive detection setup. The laser is based on a 2D grading, giving rise to the blue cross of the emitted laser light. Picture by G. Tsiminis.
Our group has developed a laser system that could be used to detect hidden explosives. The system may be able to be used to help to detect landmines and roadside bombs.
Ying Yang, Graham Turnbull, and Ifor Samuel's work has recently been published in the journal Advanced Functional Materials. The laser material is made up from a type of plastic known as polyfluorene, and is excited by a compact laser. The plastic laser is very sensitive to chemicals in the air surrounding it, including trace amounts of TNT. The laser operation changes when the concentration of TNT-like molecules around it is as low as 10 parts per billion.
"Floating above a landmine in Iraq or Afghanistan, there's a very weak, dilute cloud of vapours of explosive molecules that the bomb is made from," said Dr Turnbull. "A small number of these TNT-like molecules come into contact with a plastic film that the laser is made from, and these interact with the light-emitting molecules in the laser and switch off the light emission. The laser sensor can be reset by a blast of nitrogen gas to remove the vapour."
Ying and Graham examine the explosive detection experimental setup. Explosive vapour is introduced into the chamber at 10 parts per billion and the polymer laser's lasing threshold increases within a few seconds, indicating the presence of explosives.
Work on the use of plastic lasers for sensing explosive vapours has previously been published by this group and by a team from M.I.T., but the current work shows for the first time how rapidly the laser sensor can respond to the presence of explosive vapours, with a substantial change in the light emission in only a few seconds. The work also explores how far the molecules of the vapour can penetrate into the polymer, which determines how effectively the vapour can cause a change in the laser's output power, and will guide the design of improved sensors.
Ifor Samuel said "This technology is important because polymer lasers, since they're made of plastic, could be made very easily."
"On a dusty road in Afghanistan there are relatively few things that might give you a false positive and it certainly could have potential in that area. Essentially it's making an artificial nose for a robot dog," said Dr Turnbull.
This development was reported as the lead story in the online BBC News Science section on 7 June, after appearing in the magazine New Scientist.
Resources
• Read the paper for free
• University Press Release
• BBC News Piece
• New Scientist Piece