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A new twist in optical traps

Experts in optical trapping the University of St Andrews have been awarded a prestigious European prize for a recent paper which reported on the way that light beams can be made into “tractor beams” to push particles around in circles.

The St Andrew’s team, in collaboration with colleagues in Mexico, have been awarded the European Optics Prize 2003. Dr Kishan Dholakia of the University’s School of Physics and Astronomy will accept the award on behalf of the research team at a ceremony in Munich today (Tuesday 24th June, 2003). Dr Dholakia will be awarded a certificate and prize money of 1000 Euros and will talk about the team’s work at the European Optical Society’s annual meeting.

Dr Dholakia said: “In addition to being a major result for all involved it shows a wonderful achievement following a successful collaboration between St Andrews and a university in Mexico.”

Optical traps use properties of light to grab and hold minute objects in place. This field has seen amazing advances over the last few years.

Dr Dholakia explained: “Light is able to push things, as it has momentum. Less well known is its ability to turn very small things due to its angular momentum. Each photon (light particle) in the light beam can exert a tiny twist on small particles due to the “spin” angular momentum of the photon.

“This sort of effect has been studied for a long time. However, certain types of laser beam can exert additional twisting effects, due to the way in which the light waves spiral in the beam. The wave- fronts of the light waves (like wave crests of water waves) in laser beams with this “orbital” angular momentum are inclined to the direction of propagation, rather than being perpendicular to it as in a “normal” laser beam. The wave-fronts are rather like a helter-skelter. The multi- ringed “Bessel beam” is interesting due to certain types of this beam having these spiral wave-fronts.”;

This work has created much interest in a world-side perspective and shows new experiments that can enable a deeper understanding of the properties of light. Such light beams have special properties and can also potentially be used to spin particles creating sorters and other devices for microfluidic applications.

Dr Dholakia and his colleagues at St Andrews, Vene Garcés-Chávez and Jochen Arlt (now at the University of Edinburgh) collaborated with Karen- Volke-Sepulveda and Sabino Chávez-Cerda at INAOE, Puebla, Mexico. The prize winning paper “Orbital angular momentum of a high order Bessel light beam” was published in the Journal of Optics.

ENDS

NOTE TO EDITORS: For further information on the research, please contact Dr Vene Garcés-Chávez on Tel: 01334 463165 or email gv3@st- andrews.ac.uk

ENDS

Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook on 01334 467227, mobile 07900 050103, or email gec3@st-andrews.ac.uk Ref: European Optics Prize pr 240603 View the latest University news at http://www.st-andrews.ac.uk

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