Compiled by Photonics Spectra staff
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.