Researchers studying at the Karlsruhe Institute of Technology in Germany, have taken a tiny step towards being able to actually create a cloaking device. They were able to make invisible a tiny bump located in a layer of gold - preventing it from being detected at infrared frequencies that were nearly visible to the human eye.
Previously developed similar devices, created by a team at Duke University, worked in only two dimensions to cloak objects from microwaves, so objects could be hidden from light traveling only in one direction. The new device works in three, meaning that objects can be viewed from any angle and remain hidden.
Lead researcher Tolga Ergin explained that the cloak is composed of a grouping of crystals with air spaces between them, similar to a pile of wood. As light passes through the crystals, it bends, hiding the bump in the layer of gold beneath. The bump was extremely tiny - only .00004" high and .0005" wide - and could be seen only with a magnifying lens.
The team designed what Ergin called a "photonic metamaterial" that was able to influence the behavior of light rays. The design is based on a "carpet cloak" that was first suggested by Professor Sir John Pendry of Imperial College London. Pendry proposed the theory of having an object hidden beneath a bump, and then making the bump invisible.
"It's like a carpet mirror," Ergin said. "If you hide an object under it, there is a bump, so you see a distortion in the reflected image. We put the carpet cloak on top of that bump and it bends the light so that the distortions disappear."
Under this experiment, the reflective surface (carpet) appeared to be flat. The team used "laser writing" to create the cloak, using a tightly focused laser beam to "write" on light-sensitive material.
Ergin explained, "Wherever you put the focus spot into the material, it will harden. It's a similar process to photography - when you develop it, whatever hasn't been exposed to the laser will be washed away."
Invisibility cloaks use special materials to deflect light, radar, or other waves, that flow around an object, similar to water flowing around a smooth pebble in a babbling brook. Invisibility is different from stealth technology, which is not designed to make an airplane invisible, but instead to reduce the cross-section image available to a radar.
Professor Ortwin Hess, of the University of Surrey, called the study a "huge step forward" in demonstrating invisibility in three dimensions. He said this great achievement and the photonic materials developed by the team could be used in the future development of lenses, as well as in optical circuitry and light storage.
Hess acknowledged that a true invisibility cloak is a long way off, but Ergin's results showed a remarkable proof of the principle.
The new research is a significant step toward the future possibility of developing a true cloaking device. The experiment dealt with an extremely tiny particle, but according to Ergin, there is no limit to the size of an object you could hide with this technology, in theory.
"You could blow this up and hide a house," Ergin said, but it took his team three hours to make this microscopic structure, so to make one that is even a millimeter in size it would take a very long time. So the development of a human-sized invisibility cloak still remains a sci-fi theory - for now.