A new device invented at Harvard’s School of Engineering and Applied Sciences will absorb unprecedented levels of infrared light, expanding possibilities for thermal detection and energy harvesting.
The instrument, designed by ten collaborators from SEAS and the University of California, San Diego, consists of just 180 nanometers of vanadium dioxide layered on a sheet of sapphire. When tuned to the right temperature, it can absorb an almost "perfect" 99.75 percent of infrared light—a feat that has earned it the name Tunable Perfect Absorber, said SEAS graduate student Mikhail A. Kats, lead author of the paper that announced the invention.
Although previous devices have achieved infrared absorption also, the Absorber has a unique mechanism for tuning to different temperatures. Researchers can now control the temperature of the device and its resulting properties. For example, the Absorber acts as an insulator at low temperatures, while at high temperatures it behaves more like a metal and absorbs less light.
About halfway between these temperature extremes, the device absorbs a maximum amount of infrared light.
“We were fortunate in the magnitude effect that we achieved,” said Kats. He added that the 99 percent absorption rate significantly exceeded his expectations of 20 percent absorption.
“We expected to see a small change and we ended up seeing a huge change,” he said. “To some extent it was serendipitous that we tested this structure on the right substrate that enhanced these effects.”
Harvard’s Office of Technology Development is currently filing for patent applications and pursuing commercial licensing for the invention, which has been two-and-a-half years in the making.
“We haven’t yet made something that is in the final stage of being used commercially,” Kats said. “However, I think that it has very significant implications for anywhere where infrared light is to be detected.”
The Absorber’s applications could vary widely, Kats added—from improving infrared cameras and thermal imaging devices to detecting radiation and controlling laser output. Each use will capitalize on the device’s improved sensitivity for infrared detection and imaging.
The Defense Advanced Research Projects Agency, the Office of Naval Research, and the Air Force Office of Scientific Research were among the agencies that supported researchers involved in the project.
The invention was featured in the journal of Applied Physics Letters Monday.