Scientists from the National University of Australia have created a tractor beam that can repel objects as well as attract them.
The new technique using a hollow laser beam was able to move particles one fifth of a millimetre in diameter a distance of up to twenty centimetres – one hundred times further than previously achieved.
The team used gold-coated glass particles that they trapped in the centre of a laser beam. The energy from the laser hits the particle’s surface and is absorbed creating hotspots. Air particles colliding with the hotspots heat up and propel away from the surface causing the particle to recoil in the opposite direction.
By varying the polarisation state of the beam, for example from axial (star-shaped) to azimuthal (ring-shaped), the scientists were able to stop the particle or reverse its direction.
Image credits: andrea.pacelli / Flickr
As lasers retain their beam quality for long distances the scientists believe their tractor beam could work over metres; their lab was just not big enough to show it.
The new technique only requires a single laser beam making it versatile. Practical applications could include controlling atmospheric pollution by repelling contaminates that damage air quality, such as the sulphur dioxide emitted from coal-fired power plants.