The development of
structured synthetic materials with unusual electromagnetic properties,
so-called metamaterials have already been fabricated that have a negative
refractive index for electromagnetic waves -- bending them in the opposite
sense to light waves entering water, for instance -- which opens up completely
novel opportunities for the manipulation of light. One of these makes it
possible, in principle, to create cloaking devices that seem to make objects
disappear. Indeed, such an invisibility cloak has already been realized for
microwaves.
The necessary electromagnetic resonances arise from the
presence in the compound of chromophores, which give the molecule a
characteristic color. Chromophores resonantly absorb light in the visible
portion of the spectrum. The crucial feature of the newly synthesized molecules
is that they contain chromophore electron systems that are arranged in
parallel, separated by spacers that permit length-dependent control of
interactions between chromophores. This particular spatial configuration alters
the refractive properties of the new materials, and in ways that give rise to
novel effects. If the sign of the refractive index can be turned negative,
light impinging on the material is bent in the opposite direction to light that
interacts with a naturally occurring material or medium. "So metamaterials
could guide rays of visible light around an object, effectively rendering it
invisible," says Langhals.
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