Tag Archives: beam

Dr Vladlen Shvedov (L) and Dr Cyril Hnatovsky adjusting the hollow laser beam in their lab at RSPE. Image Stuart Hay, ANU

ANU Physicists build reversible tractor beam

We have seen use of laser tractor beams from space ships catching or repelling space ships, objects and people. Science and technology have not developed that much to achieve such feats but Physicists at the Australian National University have done something amazing to push the boundaries science and technology a bit more and closer to that goal.


ANU Laser physicists have built a tractor beam that can repel and attract objects, using a hollow laser beam that is bright around the edges and dark in its centre.

Dr Vladlen Shvedov (L) and Dr Cyril Hnatovsky adjusting the hollow laser beam in their lab at RSPE. Image Stuart Hay, ANU
Dr Vladlen Shvedov (L) and Dr Cyril Hnatovsky adjusting the hollow laser beam in their lab at RSPE. Image Stuart Hay, ANU

It is the first long-distance optical tractor beam and moved particles one fifth of a millimetre in diameter a distance of up to 20 centimetres, around 100 times further than previous experiments.

“Demonstration of a large scale laser beam like this is a kind of holy grail for laser physicists,” said Professor Wieslaw Krolikowski, from the Research School of Physics and Engineering.

The new technique is versatile because it requires only a single laser beam. It could be used, for example, in controlling atmospheric pollution or for the retrieval of tiny, delicate or dangerous particles for sampling.

The researchers can also imagine the effect being scaled up.

“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,” said co-author Dr Vladlen Shvedov, a driving force behind the ANU project, along with Dr Cyril Hnatovsky.

Unlike previous techniques, which used photon momentum to impart motion, the ANU tractor beam relies on the energy of the laser heating up the particles and the air around them. The ANU team demonstrated the effect on gold-coated hollow glass particles.

The particles are trapped in the dark centre of the beam. Energy from the laser hits the particle and travels across its surface, where it is absorbed creating hotspots on the surface. Air particles colliding with the hotspots heat up and shoot away from the surface, which causes the particle to recoil, in the opposite direction.

To manipulate the particle, the team move the position of the hotspot by carefully controlling the polarisation of the laser beam.

“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),” Dr Hnatovsky said.

“We can move smoothly from one polarisation to another and thereby stop the particle or reverse its direction at will.”

The work is published in Nature Photonics.

Source : ANU News

Dr Horst Punzmann (left) and Professor Michael Shats test their wave-generated tractor beam. Photo by Stuart Hay. Credit : ANU

Physicists create water tractor beam

Dr Horst Punzmann (left) and Professor Michael Shats test their wave-generated tractor beam. Photo by Stuart Hay. Credit : ANU
Dr Horst Punzmann (left) and Professor Michael Shats test their wave-generated tractor beam. Photo by Stuart Hay. Credit : ANU

Physicists at The Australian National University have created a tractor beam on water, providing a radical new technique that could confine oil spills, manipulate floating objects or explain rips at the beach.

The group, led by Professor Michael Shats, discovered they can control water flow patterns with simple wave generators, enabling them to move floating objects at will.

“We have figured out a way of creating waves that can force a floating object to move against the direction of the wave,” said Dr Horst Punzmann, from the Research School of Physics and Engineering, who led the project.

“No one could have guessed this result,” he said.

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The new technique gives scientists a way of controlling things adrift on water in a way they have never had before, resembling sci-fi tractor beams that draw in objects.

Using a ping-pong ball in a wave tank, the group worked out the size and frequency of the waves required to move the ball in whichever direction they want.

Advanced particle tracking tools, developed by team members Dr Nicolas Francois and Dr Hua Xia, revealed that the waves generate currents on the surface of the water.

“We found that above a certain height, these complex three-dimensional waves generate flow patterns on the surface of the water,” Professor Shats said. “The tractor beam is just one of the patterns, they can be inward flows, outward flows or vortices.”

The team also experimented with different shaped plungers to generate different swirling flow patterns.

As yet no mathematical theory can explain these experiments, Dr Punzmann said.

“It’s one of the great unresolved problems, yet anyone in the bathtub can reproduce it. We were very surprised no one had described it before.”

Source : ANU