January 25, 2013 12:00 am

It’s light, Jim, but not as we know it

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The Starship Enterprise from 'Star Trek'©Allstar

Scientists in Scotland and the Czech Republic say they have demonstrated the first true “tractor beam”, a step towards realisation of a technology that has played a starring role in science fiction dramas from Star Trek to Star Wars.

The announcement, made in a letter to the journal Nature Photonics, highlights an ability to use beams of light to manipulate physical objects – but also the gulf between space fantasy and earthbound reality.

Fictional tractor beams have been powerful enough to trap spaceships as large as a Star Trek starship or Star Wars’ Millennium Falcon. The real-life laser fields created by researchers at Scotland’s University of St Andrews and the Czech Institute of Scientific Instruments can handle particles only a few millionths of a metre across.

But the technology’s relative simplicity and ability to pull very specific particles out of a liquid medium using light alone means it could be useful in such areas of biomedicine as advanced blood testing.

“Optical sorting looks like one of the most important possible applications,” said Tomas Cizmar, research team leader, of the St Andrews School of Medicine.

Mr Cizmar acknowledged that the Scottish-Czech team was not the first to claim a breakthrough in tractor beam technology as scientists learn to use the momentum of beams of light to move particles.

Devices such as “optical tweezers” are widely used and last year, researchers at New York University announced an experimental demonstration of an “optical conveyor” they described as a “class of tractor beams”.

But Mr Cizmar said his team was the first to use a static beam that exerted a pulling force on a particle without the need for further external control, meeting what he considered to be the definition of a true tractor beam.

The breakthrough did not require any new optical technology, instead making use of greater computing power to identify the conditions that would allow the beam to exert an attractive force.

A beam of light would normally be expected to push an object away from its source. This phenomenon can itself be tapped for use by a spaceship equipped with a big enough sail, an idea broached by science fiction author Jules Verne in his 1865 novel From the Earth to the Moon and in 2010 used by Japan’s space agency to test an interplanetary “solar yacht”.

But under some conditions, light hitting a particle scatters forward instead of back, pushing the particle toward the source of the beam, said Mr Cizmar. “The interaction of the photon with the object is not like that of a billiard ball,” he said.

Unfortunately, the latest approach offers only limited fodder for science fiction fantasies.

So far, the team has pulled particles measuring no more than two micrometres or 0.00008 inches across, and Mr Cizmar said it was unlikely to be possible to use it to grab an object even the size of a football.

The relative weakness of the momentum imparted by light means a laser strong enough to move such an object would generate prohibitive amounts of heat.

Rather than gently catching a spaceship, as the tractor beams in Star Trek do, such a device would probably burn it to a crisp.

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