13 August 2008—New optical materials that bend light in unusual ways could lead to much tinier transistors, microscopes that are able to peer at smaller cellular structures, and—with a good deal of engineering—even invisibility cloaks.
Two new types of metamaterials, as the light-bending stuff is known, were developed by researchers at the Nano-Scale Science and Engineering Center at the University of California, Berkeley, and described in separate papers in Nature and Science . One is the first three-dimensional material to have a negative index of refraction, which allows it to bend light in the opposite direction of what you would expect from any other material. The other, also 3-D, doesn’t have a negative index but still provides some negative refraction, and unlike previous metamaterials, it does so in the visible part of the spectrum.
Natural materials have a positive index of refraction, which is a measure of how much they can bend a beam of light passing through them. Stick a pole into a swimming pool, and the portion below the surface appears to jut off at an angle, because of the difference between the indices of refraction of air and water. If the water had a negative index of refraction, the part of the pole below the surface would appear to be above the water.
An index of refraction has an electrical component (permittivity) and a magnetic component (permeability). Building a metamaterial with a structure having features substantially smaller than the wavelengths of light it’s meant to refract causes resonance between the atoms in the material and the photons. This reverses the permittivity and the permeability, making the refractive index negative.
This property of metamaterials opens the door to whole new ways of manipulating light. For instance, in cases when a normal lens cannot resolve anything smaller than half a wavelength of light, metamaterials could make a superlens that could resolve below this so-called diffraction limit. That could open up new possibilities in biomedical imaging, allowing scientists to look at the proteins inside cells. It would also allow the photolithography equipment used to make computer chips to build even smaller features than are currently possible without having to find new sources of smaller wavelengths.