September 09, 2010

Laser beam uses heated gas to move particles 100 times larger than optical tweezers

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Researchers from the Australian National University have announced that they have built a device that can move small particles a meter and a half using only the power of light.

The technique needs heated gas to push the particles around, it can't work in the vacuum of outer space like the tractor beams in Star Trek. But on Earth there are many possible applications for the technology. The meter-long distances that the research team was able to move the particles could open up new avenues for laser tweezers in the transport of dangerous substances and microbes, and for sample taking and biomedical research.



Andrei Rode, a researcher involved with the project, said that existing optical tweezers are able to move particles the size of a bacterium a few millimeters in a liquid. Their new technique can move objects one hundred times that size over a distance of a meter or more.

The device works by shining a hollow laser beam around tiny glass particles. The air surrounding the particle heats up, while the dark center of the beam stays cool. When the particle starts to drift out of the middle and into the bright laser beam, the force of heated air molecules bouncing around and hitting the particle's surface is enough to nudge it back to the center.

A small amount of light also seeps into the darker middle part of the beam, heating the air on one side of the particle and pushing it along the length of the laser beam. If another such laser is lined up on the opposite side of the beam, the speed and direction the particle moves can be easily manipulated by changing the brightness of the beams.

Rode said that their technique could likely work over even longer distances than they tested.

"With the particles and the laser we use, I would guess up to 10 meters in air should not be a problem. The max distance we had was 1.5 meters, which was limited by the size of the optical table in the lab," Rode said.




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