US:Researchers say they have created new paper-thin material that can bend light rays backwards, writes Rick Weissin Washington
Black is now getting blacker.
Researchers in New York reported this month that they have created a paper-thin material that absorbs 99.955 per cent of the light that hits it, making it by far the darkest substance ever made - about 30 times as dark as the US government's current standard for blackest black.
The material is made of carbon nanotubes - microscopic hollow fibres whose walls are just one atom thick. Importantly, the fibres are widely spaced, providing plenty of space to allow light in and almost no surfaces to bounce it back out. By voraciously sucking up all surrounding illumination, it can give those who gaze on it a dizzying sensation of nothingness.
"It's very deep, like in a forest on the darkest night," said Shawn-Yu Lin, a scientist who helped to create the material at Rensselaer Polytechnic Institute in Troy, New York. "It's very, very, very dark."
Scientists, however, are not satisfied. Using other new materials, some are trying to manufacture rudimentary Harry Potter-like cloaks that make objects inside them literally invisible under the right conditions.
Both advances reflect researchers' growing ability to manipulate light. The nascent invisibility cloak now being tested, for example, is made of a material that bends light rays "backwards", a weird phenomenon thought to be impossible just a few years ago.
Known as transformation optics, the phenomenon compels some wavelengths of light to flow around an object like water around a stone. As a result, things behind the object become visible while the object itself disappears from view.
"Cloaking is just the tip of the iceberg," said Vladimir Shalaev, a professor at Purdue University and an expert in the field. "With transformation optics you can do many other tricks," perhaps including making things appear to be located where they are not and focusing massive amounts of energy on microscopic spots.
US military and intelligence agencies have funded the cloaking research "for obvious reasons," said David Schurig, a physicist at North Carolina State University who recently designed and helped to test a cloaking device.
In that experiment, a shielded object a little smaller than an ice hockey puck was made invisible to a detector that uses microwaves to "see".
The first working cloaks will be limited that way, he said - able to steer just a limited part of the light spectrum around objects - and it could be years before scientists make cloaks that work for all wavelengths, including the visible spectrum used by the human eye.
Even cloaks that work on just a few key wavelengths though could offer huge benefits, making objects invisible to laser beams used for weapons-targeting, for example, or rendering an enemy's night goggles useless .
Substances that absorb every smidgeon of incoming visible light could complement existing stealth coatings that absorb radar waves, Lin said, but he and others emphasised, however, that there were also peaceful and more immediate applications.
Solar panels coated with it would be much more efficient than those coated with conventional black paint, which reflects 5 per cent or more of incoming light. Telescopes lined with it would sop up random flecks of incident light, providing a blacker background to detect faint stars.
While Lin and his colleagues pursue applications for their "superblack", others are hoping to go further by perfecting complete invisibility. The big difference is that a "superblack" object, even if invisible to the eye, still casts a shadow behind it, while an object shielded by an invisibility cloak does not.
John Pendry, a professor at Imperial College London, pioneered much of modern thinking about how to attain full invisibility using "metamaterials" - substances engineered to manhandle light. Ordinary matter, such as glass or water, slows and bends light as it passes through. "Metamaterials" contain bits of metal or other substances embedded in precise patterns to make the light bend in an opposite direction from normal paths. "In a sense you have some negative space," he said. "The light appears to go backward in space."
Pendry added a cautionary note about invisible cloaks, making a real-life distinction from the stuff of fiction: people inside them will not be able to see out. By definition, he said, if no light bounced off them, none could reach their eyes, either. "You'd have to use signals other than light to communicate," Pendry said.
Asked for an example of what would work, he paused for a moment. "You could always talk to them," he said.