Tiny “invisibility cloak” is like a magic carpet

 Researchers have created a tiny “carpet cloak” that conceals objects under it from detection using light near the human-visble part of the spectrum. While the carpet it self is visible, the bulge of the object underneath it “disappears” from the view of instruments that use this near-infrared light.



These three im ages de pict how light strik ing an ob ject cov ered with the car­pet cloak acts as if there were no ob ject. (Im age by Thom as Zent graf)

These three images depict how light striking an object covered with the car­pet cloak acts as if there were no object. (Image by Thomas Zentgraf)

(WORLD SCIENCE)   Researchers say they’re hopeful that with more precise fabrication their strategy should yield a true “invisibility carpet” that works in the area of the color spectrum utilized by human eyes, and at a larger size.


The carpet works such that shining a beam of light on the bulge shows a reflection identical to that of a beam reflected from a flat surface.

“We have come up with a new solution to the problem of invisibility based on the use of dilectric [non conducting] materials, said Xiang Zhang of the University of California Berkeley and Lawrence Berkeley National Laboratory in California, leader of the research team. 

“Our optical cloak not only suggests that true in visibility materials are with in reach, it also represents a major step to wards transformation optics, opening the door to manipulating light at will for the creation of powerful new microscopes and faster computers.”

Zhang and his team published a paper on their work in the research journal Nature Materials.

Previous work by Zhang and his group involved complex “metamaterials”—composites of metals and electrically insulating substances whose extraordinary optical properties arise from their unique structure rather than their composition. With these metallic metama te ri als, Zhang and his group found that light can be bent backwards, a property unprecedented innature.

The new cloak created by Zhang and his team is made exclusively from dielectric materials, which are of ten transparent to visible light. The cloak was demonstrated in a rectangular slab of silicon 250 millionths of a millimeter thick that serves as an optical “waveguide” that forces light waves along certain directions. Light is confined in the vertical dimension but free to propagate in the other two dimensions. 

A carefully designed pattern of holes — each 110 millionths of a milli meter wide — perforates the silicon, transforming the slab in to a meta material that forces light to bend like water flowing around a rock. In the experiments reported in Nature Mate­rials, the cloak was used to cover an area that measured about 3.8 thousanths of a millimeter by one-tenth as much.

Right now the cloak operates for light be tween 1,400 and 1,800 nanometers in wave length, meaning the light waves are slightly longer than the visible type, Zhang said. But he maintains the cloak is relatively easy to make and should be up wardly scalable. “In this experiment, we have demonstrated a proof of concept for optical cloaking that works well in two dimen­sions,” said Zhang. “Our next goal is to realize a cloak for all three dimensions.”


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