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December 18, 2006

metamaterial gives Visible light negative refraction

The race to build an exotic material with a negative refractive index for visible light has been won by a team of researchers in Germany. The demonstration could open the door to a new generation of optical devices such as superlenses able to see details finer then the wavelength of visible light.

Dolling's metamaterial is made by depositing a layer of silver on a glass sheet, covering this with a thin layer of nonconducting magnesium fluoride, followed by another silver layer, forming a sandwich 100 nm thick. Dolling then etched an array of square holes through the sandwich to create a grid, similar to a wire mesh.

Dolling determined the refractive index of the material by measuring the "phase velocity" of light as it passed through. His measurements show the structure has a negative refractive index of -0.6 for light with a wavelength of 780 nm.

This value drops to zero at 760 nm and 800 nm, and becomes positive at longer and shorter wavelengths. Previously, the shortest wavelength at which a negative refractive index had been demonstrated was 1400 nm.

The team has not yet observed some of the other exotic effects possible with a negative refractive index, such as the ability to bend light backwards. However, simulations show that negative-index lenses should produce exotic effects over a limited range of wavelengths. For now, Dolling is concentrating on studying the new effects rather than attempting to build devices such as superlenses.




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