Monday, 20 October 2014 13:41

ANU physicists build reversible laser tractor

By
Krolikowski et al, Nature Photonics Krolikowski et al, Nature Photonics

Physicists at the Australian National University (ANU) have built a tractor beam that can repel and attract objects over a much longer distance than previously achieved.

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.

Professor Wieslaw Krolikowski, from the Research School of Physics and Engineering at ANU, said the new technique is versatile because it requires only a single laser beam and could be used, for example, in controlling atmospheric pollution or for the retrieval of tiny, delicate or dangerous particles for sampling.

"Demonstration of a large scale laser beam like this is a kind of holy grail for laser physicists," said Professor Krolikowski.

The research team says it 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.

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 Cyril Hnatovsky said.

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

The work by the ANU team is published in Nature Photonics.


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Peter Dinham - retired and is a "volunteer" writer for iTWire. He is a veteran journalist and corporate communications consultant. He has worked as a journalist in all forms of media – newspapers/magazines, radio, television, press agency and now, online – including with the Canberra Times, The Examiner (Tasmania), the ABC and AAP-Reuters. As a freelance journalist he also had articles published in Australian and overseas magazines. He worked in the corporate communications/public relations sector, in-house with an airline, and as a senior executive in Australia of the world’s largest communications consultancy, Burson-Marsteller. He also ran his own communications consultancy and was a co-founder in Australia of the global photographic agency, the Image Bank (now Getty Images).

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