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  • Magnetized Common Metals Refract Negatively
Aug 2011
VIENNA, Austria, Aug. 19, 2011 — While it is generally believed that negative refraction cannot be achieved with natural materials, scientists at the Vienna University of Technology (TU Vienna) report that when common metals such as cobalt and iron are placed in a magnetic field, they too are capable of a negative refractive index.

The effect of negative refraction can be seen in nature when a stick, for example, is partly submerged in water. At the surface, the light changes its direction, and the stick appears to be bent at the interface between the air and water. For years, scientists have tried to mimic this negative refractive index, believing that these effects could be achieved only using metamaterials. Such materials, constructed from small, intricate structures, would diffract the light in special ways on a microscopic level.

The beam of light enters the metal and is refracted into the opposite direction (left) compared to the usual behavior of light in materials (right). (Image: Vienna University of Technology)

At TU Vienna, scientists found that with simple tricks, even quite common metals can exhibit a negative refractive index. “We place the metal in a strong magnetic field and irradiate it with light of precisely the correct wavelength,” said Andrei Pimenov, a professor at TU Vienna. He used microwave radiation, which can penetrate thin foils of metal. Due to magnetic resonance effects in the metal, the light is bent drastically at the surface. Within the metal, the light turns in the other direction as if there were a mirror there.

Scientists believe that this could lead to completely new optical effects and technologies.

Recently, materials with a negative diffractive index have attracted a great deal of attention, because their peculiar behavior could allow for completely new kinds of optical lenses. The resolution of regular lenses is limited by the wavelength of light.

“But using a material with a negative refractive index, one could theoretically get infinitely high resolution,” Pimenov said. Being able to use simple metals instead of complicated metamaterials makes things a lot easier. However, before optical lenses with a negative refractive index can be built, scientists have to find ways to compensate for the absorption of the light in the material, he said.

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