Only a couple of years, more than a few physicists doubted that it would ever be possible to build decent metamaterials with a negative refractive index for visible light.
Metamaterials have bulk properties that depend on the structure of their components rather than the bulk properties of the materials from which they are made. The thinking is that they can make light do all kinds of things that are no possible in naturally occurring stuff such as bending light backwards and imparting it with a reverse Doppler shift.
Metamaterials that bend microwaves backwards are straightforward to make: it’s just a question of arranging components, such as conducting wires and split rings, in a periodic 3D array on a centimetre scale.
It’s easy to think that similar structures would work for visible light were they shrunk to the nanometre scale. But, as many physicists have pointed out, the electrical properties of conducting metals do not scale with wavelength in quite the same way. Instead of transmitting light, many of these designs would be opaque to visible light.
Some people said it may never be possible to make efficient negative refraction index metamaterials for visible light. Others, who were a little more optimistic, were vindicated last August, Xiang Zhang at the University of California, Berkeley, revealed that a periodic array of parallel silver nanowires embedded in aluminium oxide worked perfectly well as metamaterial with negative refractive index for visible light.
Now Akhlesh Lakhtakia at Pennsylvania State University and pals have worked out how to make sheets of this stuff using a vapour deposition technique that is common in the optical industry.
So in a couple of years, we’ve gone from having little prospect of a negative refractive index material for visible light to a way of making sheets of it at extremely low cost.
That’ll make negative refractive index materials available to almost anybody who wants to play with them. Expect to see some ingenious applications in the coming months.
Ref: arxiv.org/abs/0903.1177: Vapor-deposited thin Films with Negative refractive Index in the Visible Regime
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