Mirrors need not be equal-opportunity reflectors.
A newly fabricated mirror reflects only a single wavelength of light; all other wavelengths pass through undisturbed. Introduced in the March 6 Physical Review Letters, the mirror is the latest device constructed from metamaterials — synthetic substances composed of structural elements that manipulate desired wavelengths of light. Similar “metamirrors” could eventually replace bulky, expensive radio dishes used for communication and astronomy.
Conventional mirrors contain a silvery layer that reflects a broad range of light, including the entire visible spectrum. The metamirror designed by physicist Viktar Asadchy and colleagues at Aalto University in Finland looks very different: It consists of millimeter-sized loops of copper wire embedded in plastic.
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Researchers illuminated the mirror with microwaves. The 60-millimeter-wavelength microwaves induced a current through the wires, which then emitted radiation that interacted with the other microwaves. By adjusting the sizes and shapes of the wires, the researchers could get the 60-millimeter-wavelength microwaves to reflect off the mirror at any angle. Microwaves at other wavelengths did not get reflected.
The team also built a metamirror that, despite being flat, mimicked a rooftop satellite television dish by reflecting and focusing microwaves toward a point. Asadchy says that a future device with nano-sized wires could reflect individual colors of visible light.