Tractor Beams 'Pull' Tiny Particles Backward

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A laser moves tiny spheres of polystyrene floating in water.
Bill Varie/Corbis

In space opera, it's not uncommon for the hero's ship to be snagged by a tractor beam that pulls him towards the enemy -- think of the famous scene in Star Wars where Darth Vader's Death Star captures Hans Solo's spaceship, the Millennium Falcon in an invisible grasp. Scientists have now made a real tractor beam, that while not capable of snaring spacecraft yet, is able to tug on tiny particles.

Pavel Zemanek and his colleagues at the Institute of Scientific Instruments of the Academy of Sciences of the Czech Republic built a laser that moves tiny spheres of polystyrene floating in water. Changing the way the light is polarized changes the direction the spheres move. They also found that at certain sizes, the spheres arrange themselves into neat rows as they move, bound by the light itself.

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"We used a relatively simple setup easily adaptable to any optical microscope and found that it works!" Zemanek told Discovery News via email. In fact Zemanek said it was so simple, one could build the tractor beam setup. All you'd need is a good microscope, a laser, tiny styrofoam balls and distilled water.

This kind of 'tractor beam' can't be scaled up to spaceships – the laser power needed to do that would end up vaporizing the intended target. But the beam could be used to assemble parts in very small robots, move around tiny particles in laboratory experiments and advance medical diagnostics.

"NASA also is actively investigating possible uses of optical tractor beams for sampling comet tails and planet surfaces. What the present paper makes clear is that tractor-beam technology also opens new avenues for lab-on-a-chip material processing that could be very useful for medical diagnostics and related applications," said David Grier, a professor of physics at New York University. Grier wasn't involved in this study.

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Scientists have known for a century that light exerts pressure. About a decade ago, theoretical calculations showed that a particle could move against the direction of a light beam, but no one had demonstrated it in the real world without using a complex arrangement of lenses and mirrors.

Zemanek and his team got it to work using laser beams and a simple setup.