Laser gun to zap leaves on line

They have blasted it, scrubbed it, sanded it and scraped it, but the humble leaf on the line has resisted everything the might of Britain's railways can hurl at it. Now, though, the commuters' most loathed excuse may finally be on the way out - zapped with a laser.

Mounted under the belly of a train, LaserThor sends pulses of an extremely fine infra-red laser beam downwards onto the track, creating 5,000C of heat and vapourising the leafy matter instantly without damaging the rail beneath.

The idea was developed by former Royal Naval Officer Malcolm Higgins, who got £360,000 from the Government to do it. He said: "They may start off as humble leaves, but put a train over them and they turn into a black Teflon-like substance that is virtually welded to the track, is incredibly slippery, and extremely difficult to move. Even scraping it off with a penknife is all but impossible.

"I am no scientist or railway expert but it suddenly occurred to me that lasers ought to be able to help."

Demonstrations for potential customers will take place this autumn.

"Railtrack has so far been interested enough to help us get safety clearance and for using its rails and locomotives to test it, so I expect they will be an early customer," said Mr Higgins. "By autumn we expect to get it up to 40mph by fine-tuning the system. That is a practical proposition for nightly maintenance. By next year, we expect to have a commercial version, and possibly one that could be mounted in an ordinary passenger train."

The system depends on a new type of laser called a pulsed neodymium yttrium aluminium garnet laser. Designed by the Fraunhofer Institute for Laser Technology in Aachen, Germany, it puts out 1kw of energy, about 10 times more than most of its rivals.

The laser itself is fitted into a stainless steel cube a metre high which also holds a chiller - to stop waste energy melting the whole device. Two small bogey wheels keep the system a constant 15mm above the track. Mounted below a standard Railtrack maintenance locomotive, it currently works at speeds of up to 20 mph.

"There is virtually no maintenance. There are no moving parts, and the diodes, which make the light for the laser, have a life of 10,000 hours. That is five years at eight hours a day every day," said Mr Higgins.

Leaves on the line, which now cost Railtrack £60 million a year, became a problem after the passing of the Age of Steam when trees started to be planted alongside tracks as noise screens.

LaserThor is reported in next month's edition of Physics World, the magazine of the Institute of Physics.