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Terahertz invisibility cloak created

Photonics Spectra
Jul 2011
Compiled by Photonics Spectra staff

EVANSTON, Ill. – A new cloaking material can render objects invisible in the terahertz range. While the design does not create an invisibility cloak for the visible spectrum, it could have applications in diagnostics, security and communications.

The cloak, created at Northwestern University, uses microfabricated gradient-index materials to manipulate the reflection and refraction of terahertz wavelengths. To render an object invisible, light must be manipulated so that it will neither scatter at an object’s surface nor be absorbed or reflected by it. To manipulate light in the terahertz frequency, Cheng Sun, an assistant professor of mechanical engineering, and his colleagues used a technique called electronic transfer microstereolithography to develop a metamaterial composed of prism-shaped structures less than 10 mm long.

The researchers used a data projector to project an image onto a liquid polymer, and then light to transform the liquid layer into a thin solid layer. Each of the prism’s 220 layers has holes that are much smaller than terahertz wavelengths, which means that they can vary the refraction index of the light and render invisible anything located beneath a bump on the prism’s bottom surface; the light then appears to be reflected by a flat surface.

The purpose of the newly created cloak was not to hide items but to gain a better understanding of how to design materials that can manipulate light propagation, Sun said.

Sun’s research into terahertz optics could lead to safer detection of certain kinds of cancers and to better ways of using terahertz scanning at airports.

Sun hopes to use the information gathered from the cloak to create its opposite: a terahertz lens. He has no immediate plans to extend his invisibility cloak to visible frequencies.

Results of his findings were presented at CLEO 2011 in Baltimore.


GLOSSARY
prism
A transparent optical element having at least two polished plane faces inclined relative to each other, from which light is reflected or through which light is refracted.
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