Device can hide, on cue, from infrared cameras

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Researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have created a device that can absorb 99.75% of infrared light that shines on it, so when activated, it appears black to infrared cameras.

Composed of a 180nm thick layer of vanadium dioxide on top of a sheet of sapphire, the device reacts to temperature changes by reflecting more or less infrared light. The team says the 'perfect absorber' is ultrathin, tunable and suitable for use in various infrared optical devices. "We exploit a kind of naturally disordered metamaterial, along with thin film interference effects, to achieve one of the highest absorption rates we've ever seen," said Federico Capasso, professor of applied physics at SEAS. "Yet our perfect absorber is structurally simpler than anything tried before, which is important for many device applications." Vanadium dioxide is normally an insulating material, but the crystal rearranges itself as temperature approaches a critical value until it becomes uniformly metallic. Near to this insulator to metal transition, the microstructure has unusual electronic and optical properties. Meanwhile, the crystal structure of the sapphire substrate actually makes it opaque and reflective, like a metal, to a narrow subset of infrared wavelengths. The result is a combination of materials that internally reflects and devours incident infrared light. As the device can be switched between its absorbent and non absorbent states, the possible applications include thermal imaging devices with tunable absorption, spectroscopy devices, tunable filters, thermal emitters, radiation detectors, and equipment for energy harvesting.