By Hannah Devlin
Scientists have come a step closer to making Harry Potter-style invisibility cloaks a reality.
Researchers at Karlsruhe Institute of Technology, in Germany, have created the first device to render an object invisible in three dimensions.
By placing a “cloak” over a tiny lump of gold measuring 0.00004 in by 0.00005 in, they were able to distort the light hitting the object in such a way that the bump appears invisible at nearly visible infrared frequencies.
Previously developed cloaks worked only in two dimensions and only worked if viewed from a specific angle. They also only worked for microwave frequencies. The new cloak works for infrared light — a step closer to the visible spectrum.
In the future, the researchers said, the cloak could be used to conceal much larger objects. “In principle, the cloak design is completely scalable; there is no limit to it," said Tolga Ergin, a scientist from the institute who led the study.
The cloak works by changing the speed and direction in which light travels through the material, factors that are defined by the material’s refractive index.
The researchers achieved this by using a polymer crystal made of tiny rods, with air spaces in between. Air has a refractive index of about 1, while the polymer has an index of 1.52. By changing the ratio of air to polymer, in principle, they could get a refractive index of anything in between.
By tailoring the refractive index of the surface of the bump, the scientists rendered it invisible to a wide range of wavelengths slightly longer than visible light.
The basis of the design is known as a “carpet cloak”, which was first proposed by Professor Sir John Pendry, who also participated in this study.
Mr Ergin said that the research would enable greater learning about the concepts of transformation optics: "We have made a first step in producing 3-D structures in that field.
“Invisibility cloaks are a beautiful and fascinating benchmark for the field of transformation optics, and it is very seldom that one can foretell what practical applications might arise out of a field of fundamental research.”
http://www.timesonline.co.uk/tol/news/s ... 068782.ece
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