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Optics

Light Throws a Curve Ball

by on Oct.21, 2008, under Optics

Light curving a path for particlesImagine shining a torch on a wall of a large dark room. The further away from the wall you are the larger and dimmer the circle of light will be. A normal light source spreads out with distance, an effect known as diffraction.

A coherent light source, such as a laser pointer, diffracts considerably less. It would throw a bright spot of light anywhere in the same room. However, the same spot would be 100 km wide by the time it reached the Moon.

Two scientists, Michael Berry and Nandor Balazs, predicted the existence of light beams that do not diffract at all in 1979. They named these beams “Airy beams” after the British astronomer Sir George Airy. Last year a group led by Georgios Siviloglou from the CREOL-University of Central Florida produced Airy beams for the first time. They showed that Airy beams could be curved.

The St Andrews team has now shown that curved Airy beams can be used to push particles along curved paths. They created what team member Joerg Baumgartl called, “a small snow-blower.” They used it clear a chamber of microscopic particles. This could be the basis of micro-engineering devices that could move and sort particles or cells.

Professor Dholakia said, “our understanding of how light moves and behaves is challenged by such beams and it is exciting to see them move into the interdisciplinary arena – light has thrown us a curve ball!”

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