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'Tractor Force' Experiment Goes Where No Man Has Gone Before

posted 15 Apr 2013, 06:47 by Mpelembe   [ updated 15 Apr 2013, 06:48 ]

Researchers are taking Star Trek 'tractor beam' technology where no man has gone before. The scientists from Scotland's University of St Andrews and the Institute of Scientific Instruments (ISI) in the Czech Republic have found a way to generate a special optical field that efficiently reverses radiation pressure of light.

BRNOCZECH REPUBLIC  (ISIBRNO.CZ/WWW.ST-ANDREWS.CO.UK) -  In the science fiction programme Star Trek tractor beams have often been used to attract large-scale objects to each other from a distance. In real life this has only been possible on a microscopic level, but a team of Czech and Scottish researchers have taken the technology into a new dimension. Dr Tomas Cizmar's team have, for the first time, managed to generate a special optical field that efficiently reverses radiation pressure of light.

Scientists hope such reverse force could have medical applications by targeting and attracting individual cells.

Usually when microscopic objects are hit by a beam of light, they are forced along in the direction of the beam, away from its source, by the light photons. That radiation force was first identified by the German astronomer Johannes Kepler in 1619 when he observed that tails of comets always point away from the Sun. But the Czech and Scottish team say they've moved tiny polystyrene beads submerged in water by reversing the process.

"Our implementation is a clear demonstration of this, that the radiation pressure for some specific parameters can reverse, so instead of pushing like sunlight pushes away comet tails, you can obtain pulling, so the particles would propagate towards the source of the light," said Cizmar. "Unfortunately it only occurs for very small particles, in the range of between half a micrometer up to say five micrometers for a visible light."

The team at the University of St Andrews worked with colleagues at the Institute of Scientific Instruments (ISI) in the Czech Republic. All the experiments were done at ISI headquarters in the Czech city of Brno (pron: Berno).

"We only used two beams, or in a sense we only used one reflected from a mirror that provided us with much simpler geometry to see this phenomena clearly. That's where the significance is, the experimental verification that something like that truly exists," explained Cizmar.

The research, published in Nature Photonics and led by the University of St Andrews, is limited to moving microscopic particles.

Practical scientific theories on real-life tractor beams have been developed since 1960, but it is thought this is the first time a beam has been used to draw microscopic objects towards the light source.

Recent years have seen a flurry of interest in the possibilities of 'tractor beam' technology. US space agency NASA has even funded a study to examine how the technique might help with manipulating and capturinge planetary particles in space.

It has been a staple plot device in science fiction, television and movies allowing objects like space ships to be trapped in a beam of light, but Dr Cizmar says this particular technique would not eventually lead to that because it would require too much heat. It could have interesting applications in the medical field, though, such as more efficient examination of blood samples.

"Our demonstration, as we've shown it, allows sorting of objects based on their size, so possibly even materials, so there is a hope that at some point this could be used for sorting of colloidal ensembles, maybe even such as blood, if you tweaked the parameters properly," Cizmar said.

Cizmar calls his team's work "a great discovery for fundamental physics" which could broaden understanding of light and matter interactions.

The Czech physicist, due to take up a new position at the University of Dundee, is working on a variety of other projects, including a lensless miniature camera no thicker than a human hair. Images can be transmitted along a tiny strand of fibre optic cable and could be harnessed to allow doctors to see inside some of the hardest to reach parts of the human body.