Thursday, November 06, 2014

Optical super reflector: for specific wavelength the light is perfectly reflected

MIT Creates World's First 'Perfect Mirror' with Zero Distortion, Signaling Breakthrough for Solar Power

Scientists at MIT just announced that they have created the perfect mirror – and it could signal a breakthrough for solar power technology. The team’s “perfect mirror” is capable of reflecting any type of wave — light, sound, or water — with absolutely zero distortion, so it could provide a huge boost to concentrated solar power installations, which use mirrors to focus concentrated beams of sunlight onto a specific area.

Ever feel like what you see in the mirror can’t possibly be accurate? Well, there’s actually some truth to that. All mirrors absorb some of the light waves that hit them or scatter photons around in different directions, resulting in slight distortion. When it comes to solar power installations, these tiny distortions can add up to big efficiency losses.
Marin Soljačić and colleagues from MIT’s photonics and electromagnetics group didn’t set out to create a perfect mirror that could eliminate these inefficiencies – as in many scientific discoveries, they stumbled upon it while investigating something else. ExtremeTech explains:
The team was studying the behavior of a photonic crystal — in this case, a silicon wafer with a nanopatterned layer of silicon nitride on top — that had had holes drilled into it, forming a lattice. These holes are so small that they can only accommodate a single light wave. At most angles, light was partially absorbed by the photonic crystal, as they expected — but with a specific wavelength of red light, at an angle of 35 degrees, the light was perfectly reflected. Every photon that was emitted by the red light source was perfectly bounced back, at exactly the right angle, with no absorption or scattering.
This work is “very significant, because it represents a new kind of mirror which, in principle, has perfect reflectivity,” says A. Douglas Stone, in a press release. Stone is a professor of physics at Yale University who was not involved in this research. The finding, he says, “is surprising because it was believed that photonic crystal surfaces still obeyed the usual laws of refraction and reflection,” but in this case they do not.
The researchers are still trying to figure out why this deviation from known scientific laws took place. However, there is some excitement about what a perfect mirror could mean for various industries. The most obvious application is more powerful and efficient lasers, but concentrated solar power and fiber optics could also be improved.

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