New device hides from infrared cameras
Now you see it, now you don’t. A new device invented at the Harvard School of Engineering and Applied Sciences (SEAS) can absorb 99.75 percent of infrared light that shines on it. When activated, it appears black to infrared cameras. 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. Announced Monday in the journal Applied Physics Letters, this perfect absorber is ultrathin, tunable, and exceptionally well suited for use in a range of infrared optical devices. Perfect absorbers have been created many times before, but not with such versatile properties. 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. Other devices incorporate surfaces with nanoscale metallic patterns that trap and eventually absorb the light. “Our structure uses...