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article imageNot just sci-fi, long-range tractor beam now a reality

By Greta McClain     Oct 21, 2014 in Science
Canberra - Two Australian laser physicists have developed the world's first first long-distance optical tractor beam, capable of not only attracting objects, but repelling them as well.
Tractor beams were once thought of as nothing more than something out of a science fiction movie. Over the past few years however, laser beams have become a reality. In January of last year Digital Journal reported that scientists had developed a tractor beam capable of targeting single cells in the human body and moving them to a particular location. However, that tractor beam only moved microscopic cells very short distances.
According to Nature Photonics, the development and use of long-range tractor beams have never evolved beyond the realm of theoretical investigation. That has now changed thanks to Australian National University (ANU) laser physicists Dr Wieslaw Krolikowski and Dr Cyril Hnatovsky.
Krolikowski and Hnatovsky have developed a long-distance optical tractor beam with the ability to move particles one fifth of a millimeter in diameter up to 20 centimeters, a distance approximately 100 times further than previous experiments. The physicists believe the tractor beam is capable of moving objects at much further distances, saying:
“Because lasers retain their beam quality for such long distances, this could work over metres. Our lab just was not big enough to show it.”
Unlike previous tractor beams, this tractor beam is also unique in the fact it used a single laser beam.
In the past, researchers have used photon momentum to create motion with tractor beams. The ANU tractor beam however depends on the energy created by the laser heating the target particles and the air around them. This was demonstrated by using gold-coated hollow glass particles.
When targeted, the glass particles become trapped in the dark center of the beam and produced energy as the laser hit the particles. This energy then traveled across the surface of the particles and created hotspots. When particles of air collide with the glass particle hotspots, the air particles bounce away from the heated surface. This causes the heated particle to recoil in the opposite direction. In order to manipulate the direction of the particle, the researchers change the position of the hotspot by controlling the polarization of the laser beam.
Hnatovsky explains the technique, saying:
“We have devised a technique that can create unusual states of polarisation in the doughnut shaped laser beam, such as star-shaped (axial) or ring polarised (azimuthal). We can move smoothly from one polarisation to another and thereby stop the particle or reverse its direction at will.”
Scientists foresee using the laser beam as a way to help control atmospheric pollution according to CNet. It can also be used to retrieve tiny, delicate or dangerous particles needed for sampling.
When asked about the development and use of the ANU tractor beam, Krolikowski calls it the "holy grail for laser physicists."
More about tractor beam, longdistance optical tractor beam, Laser physicists, Australian national university, Science
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