Invisibility Cloak Moves From
Fantasy to Potential Reality
Campus Labs Engineer Composite
Able to Reverse the Natural Direction of Light
HADAS GOSHEN / Daily Californian 19aug2008
Jie Yao, right, co-author of a science paper about new materials that can bend light backwards, gives a brief demonstration as co-authors Guy Bartal, left, Jason Valentine, center, look on during a news conference in a laboratory at the University of California at Berkeley in Berkeley, Calif., Monday, Aug. 11, 2008. Scientists say they are a step closer to developing materials that could render people and objects invisible. Researchers have demonstrated for the first time they were able to cloak three-dimensional objects using artificially engineered materials that redirect light around the objects. The new work moves scientists a step closer to hiding people and objects from visible light, which could have broad applications, including military ones.
Photo: Eric Risberg/AP source: 19aug2008
Whispers of a potential invisibility cloak are floating among the labs of UC Berkeley researchers, and contrary to notions of fact and fantasy, these are not the ravings of mad scientists.
Recent breakthroughs at campus labs have left scientists considering the possibility of designing cloaking devices that make objects invisible to human sight. They have already engineered remarkable composite materials known as "metamaterials" capable of reversing the natural direction of visible and near-infrared light.
The benefits of such materials are numerous, and according to the project's research manager Guy Bartal, the labs' two main projects are milestones for the future of light-bending research. UC Berkeley researcher Thomas Zentgraf said he believes the studies will expand scientific possibilities, making way for new designs for optical lenses or optical computers.
"As a result of a lens or microscope objective made of such a material, we would be able to get better images with much higher resolution than those possible today," Zentgraf said. "This would be very interesting for biological applications to observe living viruses or DNA directly in a normal microscope."
But the most popular discussion for the future of negative index materials remains largely on the development of cloaking devices, made possible by the metamaterials' ability to guide light around an object without disturbing the light after it passes.
"An observer would not recognize that there is an object between them and the source where the light comes from, making the object optically invisible," Zentgraf said. "Of course this sounds like science fiction, and we are still far away from doing this for visible light, but nevertheless our work is one step in this direction."
While Zentgraf maintains that cloaking devices are a long way away, UC Berkeley's metamaterials research has sparked the interest of the U.S. government, particularly the military.
In addition to funding from the National Science Foundation, the U.S. Army Research Office has given support to one of the lab's projects and the U.S. Air Force Office of Scientific Research has aided the other. Bartal says this is "not surprising," and should researchers eventually design a cloaking device, there will be military uses for it.
The grants have enabled scientists to use specially-designed nanotechnology, creating metamaterials with a negative refraction index which, unlike naturally occurring materials, enables them to bend light backwards.
"The basics of this phenomenon lies in the basics of metamaterials," said Bartal. "Using nanotechnology, we were able to design these materials comprised of very tiny elements, and when light goes through them they respond with properties that do not exist in nature, unlike glass or water or crystals that bend light naturally."
In one such case, campus researchers constructed a type of "fishnet" comprised of alternating layers of silver and non-conducting magnesium fluoride, achieving a negative refraction of light, with both electrical and magnetic fields in the light wave moving backward in the material.
While it seems invisibility cloaks are no longer confined to the world of J.K. Rowling, it's unlikely that such a product will ever be developed for mass manufacturing. The techniques used for the fabrication of lab samples was limited to small sizes, and the unique bending of light is difficult to achieve.
But with future improvements of nanofabrication techniques, Zentgraf says he is optimistic that he and his team will continue to build substantial devices out of such metamaterials.
Overhyped Material Will Not Make You Invisible
AARON ROWE / Wired 11aug2008
Hundreds of news outlets are reporting that researchers at Berkeley have discovered an amazing material, which could be used to make things invisible. Chris Lee, over at Ars Technica, did not buy into the fantastic story. He explains that the impressive substance will have many useful purposes, but a cloaking device is not one of them.
This is a classic example of what is wrong with science news. Some professor submits a paper to Nature, it gets accepted, and then a shameless media relations officer writes a misleading press release. Reporters across the globe see the press release, and churn out a story in a heartbeat, without ever bothering to question the most incredible statements.
Invisibility Cloak 'Step Closer'
BBC News 19aug2008
Scientists in the US say they are a step closer to developing materials that could render people invisible.
Researchers at the University of California in Berkeley have developed a material that can bend light around 3D objects making them "disappear".
The materials do not occur naturally but have been created on a nano scale, measured in billionths of a metre.
The team says the principles could one day be scaled up to make invisibility cloaks large enough to hide people.
The findings, by scientists led by Xiang Zhang, were published in the journals Nature and Science.
The light-bending effect relies on reversing refraction, the effect that makes a straw placed in water appear bent.
Previous efforts have shown this negative refraction effect using microwaves—a wavelength far longer than humans can see.
The new materials instead work at wavelengths around those used in the telecommunications industry—much nearer to the visible part of the spectrum.
Two different teams led by Zhang made objects made of so-called metamaterials—artificial structures with features smaller than the wavelength of light that give the materials their unusual properties.
One approach used nanometre-scale stacks of silver and magnesium fluoride in a "fishnet" structure, while another made use of nanowires made of silver.
Light is neither absorbed nor reflected by the objects, passing "like water flowing around a rock," according to the researchers. As a result, only the light from behind the objects can be seen.
Cloak and shadow
"This is a huge step forward, a tremendous achievement," says Professor Ortwin Hess of the Advanced Technology Institute at the University of Surrey.
"It's a careful choice of the right materials and the right structuring to get this effect for the first time at these wavelengths."
There could be more immediate applications for the devices in telecommunications, Prof Hess says.
What's more, they could be used to make better microscopes, allowing images of far smaller objects than conventional microscopes can see.
And a genuine cloaking effect isn't far around the corner.
"In order to have the 'Harry Potter' effect, you just need to find the right materials for the visible wavelengths," says Prof Hess, "and it's absolutely thrilling to see we're on the right track."