image: Physicists have created a tractor beam that can transport biological cells in three dimensions and could, in the future, send these beams into comets to pull out dust samples in space probe missions.
A tractor beam can pull microscopic particles and has a range of potential uses, from microfluidics to far-out tasks like grabbing dust from comet tails.
“This is science fiction made real,” says David Grier, physics professor at New York University and one of the paper’s co-authors. “This tractor beam moves objects back to its source, just like those in so many sci-fi movies, but with very small pieces.”
The so-called optical conveyor tractor beam builds upon an earlier Grier creation: optical solenoid, or spiraled, beams, which can be used to confine and pull small objects—a couple micrometers in size—over a range of eight micrometers.
By contrast, the conveyor tractor beam has demonstrated moving particles distances of 30 to 40 micrometers. Together, they are the only working tractor beams in the world.
“The field of tractor beams is really in its infancy,” says doctoral student David Ruffner, and the paper’s other co-author. “There is great potential for advances.”
Published in the journal Physical Review Letters, the work applies Newton’s third law of motion: for every action, there is an equal and opposite reaction. In this case, the action is the scattering of the beam off the particle and the reaction is the motion of the particle. In principle, this is akin to shooting a watermelon seed using your thumb and forefinger—if you grasp the seed in the right location, you can shoot the seed toward you rather than away.
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