Two lasers might work even better
(Image: Russell Tate/Getty Imagest)

Tractor beam
built from rings of laser light

18:05 19 October 2012 by Jacob Aron

Stand aside, Wesley Crusher: there’s a new tractor beam on deck that pulls objects using nothing more than laser light. The device has already grabbed NASA’s attention as it could one day prove useful on space missions.

It is well known that light can push on objects – this is the basis for using solar sails to propel a spacecraft. But getting light to pull on something is a bit trickier.

Previous laser-based tractor beams could act like tweezers to move particles, picking up the sample and putting it down a short distance away. A more recent version actually pulls on particles, but relies on temperature variations in the beam, which means it cannot function in space.

In 2011, researchers in China calculated that a type of laser called a Bessel beam, which puts out light in concentric rings, could be designed to make a particle inside the beam emit photons on the side facing away from the beam source. These photons should allow the particle to recoil towards the source. But nobody has so far managed to put the idea into practice.

David Ruffner and David Grier of New York University instead projected two Bessel beams side by side and used a lens to angle them so that they overlapped, creating a pattern of alternating bright and dark regions. Fine-tuning the beam caused photons in the bright regions to scatter toward the beam source, pushing a particle in the beam to the next bright region. The beam thus acts like a conveyer belt, constantly drawing the particle toward the source.

Read more: Tractor beam built from rings of laser light – physics-math – 19 October 2012 – New Scientist.

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