Science

Reversible tractor beam can repel and attract objects

Reversible tractor beam can re...
Dr Vladlen Shvedov (left) and Dr Cyril Hnatovsky (right) with a magnified projection of the "hollow" laser beam (Photo: Stuart Hay, ANU)
Dr Vladlen Shvedov (left) and Dr Cyril Hnatovsky (right) with a magnified projection of the "hollow" laser beam (Photo: Stuart Hay, ANU)
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Dr Vladlen Shvedov (left) and Dr Cyril Hnatovsky (right) with a magnified projection of the "hollow" laser beam (Photo: Stuart Hay, ANU)
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Dr Vladlen Shvedov (left) and Dr Cyril Hnatovsky (right) with a magnified projection of the "hollow" laser beam (Photo: Stuart Hay, ANU)

We're still a far cry from Star Trek's ship-towing and repelling technology, but laser physicists at the Australian National University (ANU) have built a tractor beam that can repel and attract objects. The beam moved spherical glass shells one fifth of a millimeter in diameter across a distance of up to 20 centimeters (7.87 in), which is around 100 times further than previous experiments at this scale, using only a single hollow laser beam that's bright around the edges and dark in its center.

The ANU researchers previously developed a similar device that moves very small particles over long distances using an optical vortex that created something called photophoretic force, which pushes the particle into a dark hollow in the center of the beam as the momentum of the photons drives it forward.

This new technique builds on the previous study, with energy from the laser heating the surrounding air particles to create hotspots on one side of the glass shell's surface. The heat drives air particles away, causing the tiny shell to recoil – thus propelling it in the opposite direction. And by altering the polarization of the laser beam on the fly, switching for instance from axial (shaped like a star) to azimuthal (like a ring), the researchers can cause the shell to change direction or stop.

The beam could have broad applications in the real-world, the researchers believe, as a means of controlling or sampling atmospheric pollution, and it could be scaled up to work over several meters. "Our lab just was not big enough to show it," explained co-author Dr Vladlen Shvedov.

It may not sound like much, but this is a big step forward in the quest to develop optical tractor beams like those from science fiction. Long-distance optical tractor beams were previously restricted only to theory – a concept that in essence sees particles, the environment, or an object's electromagnetic field manipulated by "negative forces" from lasers or Bessel beams.

"Demonstration of a large-scale laser beam like this is a kind of Holy Grail for laser physicists," said co-author Wieslaw Krolikowski. Now that the concept's been proven, the agonizing (and possibly futile) wait for something truly large scale, like the Starship Enterprise towing another ship to safety or the portal-creating, cube-moving Aperture Science Handheld Portal Device used in the game Portal, begins.

A paper describing research appeared in the journal Nature Photonics.

Source: Australian National University

6 comments
zevulon
it is not the laser causing the particles to move , it is the air around the the beads. the beads are not off gassing, they are designed to heat up the air around the beads. as there is no air in outer space, this design could never ever work in outerspace. even if you could provide your own air, you'd run out of off gassed air awfully quickly unless you had a trap for the off gassed air, in which case the trap would be absorbing inertia and slowing down the trap device in the opposite direction you are accelerating the gas, so the effect would be cancelled out. this kind of device, is likely to be useless in transportation of any kind. furthermore laser 'ablation' rocket to space devices have been around for a while and they are not very good. using laser to heat things up is generally a good way to of destroying or igniting those things, not propelling them.
inchiki
Reading your 'related articles' it sounds as if the ANU scientists did the same thing with a laser a couple of years ago.. what makes it different this time isn't really clear. Those ANU laser people are great though. A new laser based gravity wave detector is being turned on next year.
Ryan Gibbons
Meh... Not exactly what I thought it would be.
hkmk23
Exactly as other comments, I suggest that if they tried this in a zero atmosphere (outer space) it simply would not work. Now if they could attract and repel the atoms of a structure (and not a magnet), that would be exciting.
George Shorter
Beam me up.
attoman
This approach is a good tool for particulate manipulation in microscopy. Perhaps in a fluid as well as the demonstrated gas. It is not in any way a step forward for tractor beams as suggested by the hype.