A student has made a breakthrough in developing an invisibility cloak by designing an optical device that can slow down light.
The optical device, known as an 'invisible sphere', would slow down all of the light that approaches a potential cloak, meaning that the light rays would not need to be accelerated around the cloaked objects at great speeds ― a requirement that has limited invisibility cloaks to work only in a specified region of the visible spectrum.
The research published in the Institute of Physics and German Physical Society's New Journal of Physics, could open up the possibility for a potential invisibility cloak wearer to move around amongst ever-changing backgrounds of a variety of colours.
Hungarian-born Janos Perczel, an undergraduate student at the University of St Andrews, was able to work on the idea of superluminal propagation and fine-tune the invisible sphere to make it a suitable background for 'cloaking'.
"Once the idea [of superluminal propagation] was present, I worked for over eight months to overcome the technical barriers and to make the proposal practicable," Perczel said.
The usual approach to designing an invisibility cloak works on the basis of bending light ― using highly specific materials ― around an object that you wish to conceal, thereby preventing the light from hitting the object and revealing its presence to the eye of the observer.
When the light is bent, it engulfs the object, much like water covering a rock sitting in a river bed, and carries on its path making it seem as if nothing is there.
Light, however, can only be accelerated to a speed faster than it would travel in space under certain conditions, and this restricts invisibility cloaks to work in a limited part of the spectrum ― essentially just one colour.
This would be ideal if somebody was planning to stand still in camouflage; however, the moment that they start to move the scenery will begin to distort, revealing the person under the cloak.
By slowing all of the light down with an invisible sphere, it does not need to be accelerated to such high speeds and can therefore work in all parts of the spectrum.
"This new development opens up further possibilities for the design of a practical invisibility cloak ― overcoming the problem of light speed that other advances have struggled to address and, very impressively, this significant advance was achieved by an undergraduate student," said a spokesperson for the Institute of Physics.
See the full paper on "Invisibility cloaking without superluminal propagation"