Invisibility cloak, once fantasy, now potential reality at UC Berkeley

UC-BERKELY — Whispers of a potential invisibility cloak are floating among the labs of Univeristy of California 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.

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