Invisibility Cloak Edges Closer to Reality

(March 18) -- Harry Potter's version was certainly handy. Frodo Baggins used one to save himself on a few occasions. Ricky Gervais sidekick Karl Pilkington mused about what it would be like to shop with such abilities. So where are the invisibility cloaks for the rest of us?

They are still more fiction than fact, according to experts, but scientists have been making great progress over the past five years. The latest leap is described in the March 19 issue of the journal Science: German physicists constructed an extremely tiny, so-called "carpet cloak" that rendered a bump on a gold surface partially invisible.

Previously, scientists had accomplished the feat in two dimensions, meaning that the trick worked only if viewed from a certain angle. But the German group, led by physicist Tolga Ergin of the Karlsruhe Institute of Technology, designed a cloaking structure that is effective from almost any perspective.

"This is very nice work," Duke University electrical engineer David Smith, one of the leaders in the field, wrote to AOL News in an e-mail. "What is impressive is the technique used to make the structure -- it's very clever."

There are several kinds of cloaks under development today in labs across the world, but they all work by bending light. To design one, Ergin explained to AOL News, the scientists start by outlining the desired properties. "You can say I want to have a device this size," he said, "and it should bend the light that comes in from the bottom 90 degrees to the left."

Normally, a bump on a flat surface would be easy to see because light rays bouncing off that mound would take different paths relative to those that hit the surrounding area. The trick, Ergin said, is designing a structure that makes all these rays behave as if they hit the flat surface, as if the bump were not even there. This portion of the work is done in simulation. "And then of course you have to build it," he said.

To do so, Ergin and his colleagues used a high-intensity laser to essentially carve their 3-D cloak out of layers of light-sensitive material. The entire device is tinier than the thickness of a human hair. "It is quite small," Ergin notes. "You can barely see it with your eye."

So why not just build a larger one? Ergin explained that it takes about three hours to make that microscopic device; developing one capable of cloaking large objects or even people would take forever with current techniques.

This particular cloak has other limitations as well. No scientists have been able to develop a cloaking device that manipulates the visible light that our eyes see. Instead, these techniques all work on longer wavelengths -- infrared and microwave light, for example. To bend visible light, the scientists would need to build structures that operate at an even smaller scale. "Right now, we're not able to fabricate 3-D structures of this size," Ergin said. "It's just too small."

Yet that doesn't mean he and his colleagues won't try. "It gets more and more demanding if you want to go to visible light," he said. "But that's what we all want. That's the big goal."