Composed of just a 180-nanometer-thick layer of vanadium dioxide (VO2) on top of a sheet of sapphire, the device reacts to temperature changes by reflecting dramatically more or less infrared light. In a Fabry-Pérot cavity, for instance, two mirrors sandwich an absorbing material, and light simply reflects light back and forth until it's mostly all gone.
"Both of these materials have lots of optical losses, and we've demonstrated that when light reflects between lossy materials, instead of transparent or highly reflective ones, you get strange interface reflections," explains lead author Mikhail Kats, a graduate student at SEAS. "
Because the device can be easily switched between its absorbent and non-absorbent states, the possible applications are quite wide ranging and include bolometers (thermal imaging devices) with tunable absorption, spectroscopy devices, tunable filters, thermal emitters, radiation detectors, and equipment for energy harvesting.
"An ideal bolometer design needs to absorb all of the infrared light that falls on it, turning it to heat, and correspondingly its resistance should change a lot per degree change in temperature," notes Kats.