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| MIT Creates The First Perfect Mirror |
Physicists at MIT have created the first perfect mirror. When light hits the mirror — or indeed any other kind of wave, including acoustic and water waves – it bounces off perfectly, introducing no distortion and exactly preserving the original image (signal). While this is primarily big news for narcissistic MySpacers, these perfect mirrors could also lead to breakthroughs in solar power, lasers, fiber optic networks, or just about anything that involves the reflecting or capturing of light.
Conventional mirrors all work in a very simple way: they block the passage of light (or sound, or water, or radio waves), and so they have no choice but to reflect. As you can imagine, the reflection is never perfect, with some energy being absorbed by the material, or scattered in different directions. For a human checking their hair or makeup, this lack of perfection doesn’t matter; but when you’re talking about reflecting lasers down a hundred miles of optic fiber, or solar power installations, these tiny imperfections can cause a huge drop in efficiency.
Marin Soljačić and colleagues from MIT’s photonics and electromagnetics group stumbled across this perfect mirror almost by accident. 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 phenomenon is new and unexpected. John von Neumann, one of history’s most notable polymaths, theorized a similar phenomenon in 1929, but it had never been demonstrated experimentally. “It’s a very different way of confining light,” Soljačić says. A. Douglas Stone, a Yale professor who wasn’t involved with the work, says that this is practical demonstration is “very significant, because it represents a new kind of mirror which, in principle, has perfect reflectivity.”
While there are almost undoubtedly practical applications for these perfect mirrors, the MIT team is currently focused on sussing out exactly what’s going on. New phenomena, once they’re understood and easily replicated, often lead to very new and novel applications. In this case, the most obvious application is more powerful and efficient lasers, but concentrated solar power (using mirrors to boil water), and fiber optics could also be improved. Only last week we wrote about DARPA’s hollow-core fiber optics, which use photonic crystals to propagate the signal — presumably, perfect mirrors could be used in these fibers to provide greater range and speed.
DARPA’s hollow-core photonic-bandgap optic fiber
Different photonic crystals with different patterns of drilled holes should be able to reflect waves with other properties, too, such as acoustic, water, and radio. And hey, wouldn’t a perfect mirror also be useful for making an invisibility cloak…?
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