German scientists have created a metamaterial with a negative refractive index for far red light:

The trick is to assemble an array of electronic components that resonate with the electric and magnetic fields of the light waves as they pass through. These materials are unlike any conventional substance, hence the name "metamaterial". Pendry suggested that an array of coils and wires much smaller than the wavelength of light would do the trick and first demonstrated the idea for radio waves with a frequency between 15 and 20 megahertz.

Later experiments extended the technique to shorter wavelengths, first into the microwave region and later the infrared. Now Gunnar Dolling at the University of Karlsruhe in Germany, and colleagues, have demonstrated the effect at 780 nanometres - the long-wavelength end of the red spectrum - by scaling down a structure he had developed for infrared wavelengths.

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.

They speculate that this material could be used in lens or to create invisibility cloaks. My suspicion is such things are a long way off, but it is still pretty damn cool.

Hat-tip: Slashdot.