The cloak was designed to make objects invisible to infrared light, but the work paves the way for more advanced materials. Some scientists believe cloaking materials could be used to hide high-security facilities or even make vehicles seem disappear.
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 the material’s refractive index.
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.
It is for the first time that 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. 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 the object.
“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.”
As yet, scientists have not been able to make objects invisible to the eye, because visible light is more difficult to manipulate in the right way.