A working tractor beam has now been caught on video, showing how light can pull objects - on a microscopic scale.
While it's well known that light can push objects as they follow the flow of photons, attracting them isn't as simple. By shining a laser through a lens and mirror set-up, Tomas Cizmar from the University of St Andrews in the UK and colleagues were able to reverse the effect, thanks to the interference pattern of reflected beams. Their technique works both in liquids and in a vacuum.
In this video, the first clip shows how the system can be used to separate objects of different sizes. When a tractor beam in the centre of a mixture of particles is turned on, large spheres move left towards the light, while aller ones are pushed to the right.
A second clip shows how the beam can pull a collection of particles. "When the right configuration of particles occurs the tractor beam makes it stable and the whole structure moves against the tractor beam," says Cizmar.
The technique has medical applications: by targeting and attracting certain types of cells, it could, for example, help sort components of blood samples. Another recent tractor beam system attracted NASA's attention as a way of collecting dust or atmosphere samples on space missions.
If you enjoyed this post, watch how light can create instant origami or see how to play a tiny game of Tetris with a laser.
