Scientists at the University of St Andrews have developed a tractor beam, a device which uses light to attract microscopic particles. Their work was published in Nature Photonics. Tractor beams feature prominently in science fiction, notably in the Star Trek and Star Wars franchises, where they are used to move large objects such as spacecraft. Here’s a film, showing what I mean.
Now this science fiction idea has become reality – albeit on a much smaller scale.
When a beam of light hits microscopic objects, they are usually forced along in the direction of the beam by the momentum of photons, the little packets of energy that make up light. This new technique reverses that force, meaning a light beam hitting microscopic objects a few hundred nanometres in size such as individual molecules can attract them towards it. You can watch a video of the beam in action here.
Whilst the technique is new, it has great future potential. The tractor beam is selective in the properties of the particles it acts upon, so could be used to pick up and move specific particles in a mixture for example those of a particular size. NASA has studied how the technique might help with manipulating samples whilst on space explorations.
The downside of the technique is that there is a significant transfer of energy. On a microscopic scale that doesn’t matter so much, but on an everyday scale this would cause huge problems. Increasing the power of the laser, as would be required to provide enough energy to move larger objects, would make it so powerful it would just destroy the object. Because of this, making a real-life tractor beam that can manoeuvre a spacecraft wouldn’t be possible.
Despite this, it’s still a huge scientific step forward in using light in technological applications. The technique could be used for intricate engineering or in medical testing, such as to analyse blood samples.
IMAGE: Deviant Art