Download Light Hits Near Infinite Speed in Silver-Coated Glass

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Light hits near infinite speed in silver-coated glass
17:33 07 January 2013 by Jeff Hecht
A nano-sized bar of glass encased in silver
allows visible light to pass through at near
infinite speed. The technique may spur
advances in optical computing.
Metamaterials are synthetic materials with
properties not found in nature. Metal and
glass have been combined in previous
metamaterials to bend light backwards or to
make invisibility cloaks. These materials
achieve their bizarre effects by manipulating
the refractive index, a measure of how much
a substance alters light's course and speed.
Blink and you'll miss it, a million times over (Image:
John Renstenzefa/Superstock)
In a vacuum the refractive index is 1, and the
speed of light cannot break Einstein's
universal limit of 300,000 kilometres per
second. Normal materials have positive indexes, and they transmit at the speed of light in a
vacuum divided by their refractive index. Ordinary glass, for instance, has an index of about 1.5, so
light moves through it at about 200,000 kilometres per second.
No threat to Einstein
The new material contains a nano-scale structure that guides light waves through the metal-coated
glass. It is the first with a refractive index below 0.1, which means that light passes through it at
almost infinite speed, says Albert Polman at the FOM Institute AMOLF in Amsterdam, the
Netherlands. But the speed of light has not, technically, been broken. The wave is moving quickly,
but its "group velocity" – the speed at which information is travelling – is near zero.
As a feat of pure research, Polman's group did a great job in demonstrating the exotic features of
low-index materials, says Wenshan Cai of the Georgia Institute of Technology, who was not
involved in the work.
Practical applications might also be in the offing. The metal component that reduces the refractive
index also increases absorption, so the light can't travel far, says Polman. Still, the material could
be used to transmit light rapidly over the very short distances in optical integrated circuits, he says.
Journal reference: Physical Review Letters, doi.org/j5x
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