Scientists are a step closer to creating a Star Trek-style cloaking device after demonstrating a material that makes objects beneath it appear to vanish.
The material was used to hide a bump on a surface by interfering with the way light bounced off it, making it seem as though neither the cloak nor the bump was there.
The cloak was designed to make objects invisible to infrared light, but the work paves the way for more advanced materials capable of cloaking objects in visible wavelengths.
Some scientists believe cloaking materials could be used to hide unsightly buildings or high-security facilities, and even make vehicles seem to disappear from view.
Tolga Ergin and Nicolas Stenger at the Karlsruhe Institute of Technology in Germany used a technique called direct laser writing lithography to create a sheet of cloaking material from tiny plastic rods. The spacing of the rods, each of which measured one thousandth of a millimetre wide, alters a property of the material known as the refractive index, which changes the speed of light inside it.
The researchers placed a piece of the material over a dimple in a gold sheet and used infrared cameras to see what happened. When the cloak was in place, it altered the speed of light around the bump in such a way that the gold sheet appeared to be flat. The experiment was equivalent to hiding something under a carpet and having the carpet disappear too.
It is the first time researchers have demonstrated a cloak that works in three dimensions. Previous devices have hidden objects when looked at head-on, but did not work if viewed from the side. "We were surprised that the cloaking effect was still so good, Ergin told the US journal, Science.
Inside the material, the plastic rods are arranged like planks of wood piled up on each other. The high precision of the structure means it is possible to control the refractive index so it varies in just the right way to bend light around whatever object is hidden beneath it.
"The material has a higher refractive index on top of the bump, so light hitting that part is slowed down a little bit compared with light impinging on the rest of the surface," said Stenger. "That compensates for the shape of the bump, and in the end, it is exactly as if there was no bump."
Research into cloaking devices has attracted funding from military organisations, such as the US Defence Advanced Research Projects Agency, which backs high-risk science research for the Pentagon. In the near term, cloaking materials are expected to be used to hide aircraft from radar more effectively.
As yet, scientists have not been able to develop cloaking materials that make objects invisible to the eye, because visible light has shorter wavelengths that are more difficult to manipulate in the right way.
Beyond military applications, cloaking devices are drawing interest from telecommunications companies, who see them as a way to send information by light more efficiently. One idea is to use the new materials to build "superantennas" that can concentrate light and other electromagnetic waves to make laser-like beams.
"We are focusing on a new way to control light," said Stenger. "In the future of technology, light is goining to have more and more importance.