Metamaterials Reflect Visible Light

David L. Shenkenberg

Metamaterials could permit the creation of ultrahigh-resolution lenses and could even make cloaking devices a reality. To do so, they must reflect visible light. In the past, they could operate only in the microwave and far-infrared ranges, but have moved into the visible region.

Making the new metamaterials proved difficult because the metals employed absorbed too much energy and their small size prevented easy manipulation. Researchers at Iowa State University in Ames and Universität Karlsruhe and Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft, both in Germany, developed them.

The metamaterials consisted of two layers of silver “fishnets” with a magnesium fluoride dielectric. The scientists used silver because it loses less energy than gold. To create the fishnets, they used a focused ion beam to etch an array of 100-nm-wide holes in the silver. A representative silver fishnet measured 100 × 100 μm.

By comparing transmittance, reflectance and time-of-flight experimental data with theoretical predictions, the researchers concluded that the metamaterial has a refractive index of –0.6 at a 780-nm wavelength, as described in the Jan. 1 issue of Optics Letters and the Jan. 5 issue of Science.

Although the new metamaterials reflect visible light, the researchers noted that their construction remains difficult and will obstruct mass production. Furthermore, energy losses within them are still undesirable. They mentioned that energy losses may be reduced by using crystalline metals and optically amplifying materials. In addition, they promoted further exploration of 3-D structures and isotropic designs.