Glass invisibility cloak shields infrared

PORTLAND, Ore. — Invisibility cloaks cast in chalcogenide glass can render objects invisible to infrared frequencies of light, according to researchers at Michigan Technological University.

Created by professor Elena Semouchkina and others at Michigan Tech and Pennsylvania State University, the glass cloak is currently being adapted to work in visible wavelengths.

Most other demonstrations of invisibility cloaks have used metamaterials composed of free-space split-ring resonators that were constructed from metal printed-circuit board traces surrounded by traditional dielectric material. The Michigan Tech researchers have already demonstrated such cloaks at microwave frequencies. They now claim that by substituting nonmetallic glass resonators made from chalcogenide glass, infrared cloaks are possible too.

Metamaterials work by resonating at the frequency to be cloaked, bending incident waves up around objects and then back down so that the light emerges on the other side as if unimpeded, effectively "cloaking" the object from view. Traditional materials can bend light only in one direction—called normal—making cloaking impossible, but metamaterials allow waveforms to be bent in any direction, permitting regions to be rendered invisible.

The metamaterial patterns must be of a size that matches the wavelength of light to be cloaked, meaning that smaller resonators are required for infrared and visible light. Traditional, pc-board based resonators work only at the millimeter wavelengths of microwaves. Infrared operates at micron-sized wavelengths; hence the need for smaller resonators.

The Michigan Tech infrared cloak uses tiny chalcogenide glass resonators arranged in a concentric pattern in the shape of the region to be cloaked—in this case, a cylinder—with spokes on the circular ends providing the magnetic resonance required to bend light waves around the region.

Semouchkina worked with fellow Michigan Tech researcher George Semouchkin and with Penn State researchers Douglas Werner and Carlo Pantano. The National Science Foundation provided funding.