New laser technology can make objects invisible

Scientists have developed a cloaking technology that can make opaque materials invisible by using light waves from lasers, paving the way for novel ways of camouflaging objects.

A completely opaque material is irradiated from above with a specific wave pattern - with the effect that light waves from the left can pass through the material without any obstruction. The technique can be applied to different kinds of waves, and should work with sound waves just as well as with light waves, researchers said.

"Complex materials such as a sugar cube are opaque, because light waves inside them are scattered multiple times," said Stefan Rotter, from Technische Universitat Wien (TU Wien) in Austria. "A light wave can enter and exit the object, but will never pass through the medium on a straight line. Instead, it is scattered into all possible directions," said Rotter. For years many different attempts have been made to outwit this kind of scattering, creating a "cloak of invisibility."

"This sounds strange, but with certain materials and using our special wave technology, it is indeed possible," said Brandstotter. To make the laser shine, energy has to be supplied by means of a pump beam. Otherwise, the laser material behaves just like any other material - it absorbs part of the incident light. "The crucial point is to pump energy into the material in a spatially tailored way such that light is amplified in exactly the right places, while allowing for absorption at other parts of the material," said Konstantinos Makris from the University of Crete in Greece.

"To achieve this, a beam with exactly the right pattern has to be projected onto the material from above - like from a standard video projector, except with much higher resolution," said Makris. If this pattern perfectly corresponds to the inner irregularities of the material which usually scatter the light, then the projection from above can effectively switch off the scattering, and another beam of light travelling through the material from one side can pass without any obstruction, scattering or loss.