Seeing is believing: scientists make invisibility cloak

By Jennifer Macey
Updated Fri Mar 19, 2010 8:40pm AEDT

It sounds like something out of a Harry Potter book, but German scientists say they have created a three-dimensional invisibility cloak.

The researchers have been able to hide a bump on a gold plate using "metamaterials", making the gold plate appear flat in infrared light.

Tolga Ergin from the Karlsruhe Institute of Technology led the research, which was published Friday in the journal Science.

"You could imagine you have a flat gold mirror and you could put an object on that mirror," he said.

"An observer could immediately tell that there is a bump there and that there is an object hidden.

"Now we can put the three-dimensional carpet cloak on top of that bump so that the bump disappears - so the observer would again see a flat mirror."

The scientists have created what is known as a metamaterial, which is used to cloak an object.

These metamaterials are tailored to change the way light bounces off something, making light bend around an object to render it invisible.

Dr David Powell from the Centre for Linear Physics at the Australian National University says the metamaterials offer the flexibility needed to do this.

"One of the applications of metamaterials is this cloaking," he said.

"And the idea is that because you have these extra degrees of freedom with these metamaterials that you just can't get with normal materials, you can bend light in these weird and wonderful ways."

Unprecedented use

It is the first time these metamaterials have been used to hide a 3D object in infrared light.

Mr Ergin says scientists in the past have managed to hide 2D or 3D materials, but in different wavelengths such as microwaves, which are not visible to the human eye.

"We've built the first three-dimensional cloaking structure which works at the optical regime," he said.

"That is very close to visible light [although] it is not in the visible regime. It is still in the infrared, but it's not very far away.

"There have been experiments on these carpet cloak designs but they have been conducted in the microwave regime, for example, or also in the optical regime but only in the two-dimensional wave guide geometry."

Dr Powell says it is a significant step forward.

"All the other proof-of-principle experiments have just been two-dimensional, which is nice proof that the idea works," he said.

"But obviously we live in a three-dimensional world and you want to prove that this idea still can be feasible in three dimensions.

"It's done over a very wide range of wavelengths, so that means that of course we see a variety of wavelengths ourselves that corresponds to all the different colours we see.

"For a real cloak to work so that we can see something it would also have to work for a large number of wavelengths and that's actually quite an achievement."

Both scientists agree though that a Harry Potter-sized invisibility cloak is still many decades away.

Mr Ergin says his experiment was on a very small scale, with the bump on the gold mirror only visible under a microscope.

But he says the technology may have many more applications than simply hiding things.

He says these advances in optics could one day be used in telecommunications or computer technology or simply to further scientific knowledge.

"These invisibility cloaks are for us just [a] beautiful, exciting and thrilling benchmark, an example to see or to look into the fundamental principles of transformation optics," Mr Ergin said.

From: http://www.abc.net.au/news/stories/2010/03/19/2851100.htm