Ultra-thin perfect absorber employing a tunable phase change material

New device hides, on cue, from infrared cameras

November 26, 2012

Tunable material developed at Harvard boasts nearly 100% absorption on demand

Cambridge, Mass. - November 26, 2012 - 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% 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 today in the journal Applied Physics Letters, and featured on its cover, 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.

Reflectivity of Mineral Powders

From the Website of Ocean Optics, an applications note for their Jaz Spectrometer

It begins:

"Reflectance spectroscopy is a versatile technique than can be used to identify and characterize a range of powdered samples including mineral powders, grains in lunar samples, mining samples, natural deposits, soils and sediment core samples. In this application note, reflectance spectroscopy is used to characterize mineral powder samples.

"The Jaz spectrometer was used to acquire reflectance spectra for pure samples and powder mixtures to assess the power of reflectance spectroscopy to characterize mineral powder samples."

Figure-3-Experiment-Setup.jpg from the Ocean Optics Blog