From research conducted at the Karlsruhe Institute of Technology (KIT)

Refining the Karlsruhe invisibility cloak

Material that allows us to purposefully direct light can be used to make objects invisible. This unusual property can be generated in so-called metamaterials by targeted microstructuring processes – but only for particular wavelengths of light and, until recently, only from a fixed direction of view (2D).

Photo electron microscope from above — Electron microscope photos of a tiny invisible cloak structure that resembles a pile of logs. In the region around the small depression, the refraction index for electromagnetic waves in the optical field changes continually. Photo/Graphic: CFN/KIT.

electrone microscope from inside — The metamaterial made from a polymer-air mixture is coloured blue, and the areas coated with gold are yellow. Photo/Graphic: CFN/KIT.

view from above — Photo/Graphic: CFN/KIT.

Photo red light invisble — In the region around the small depression, the refraction index for electromagnetic waves in the optical field changes continually. This influences light waves in such a way as to make the surface appear flat (in red light). Photo/Graphic: CFN/KIT.

The members of the group led by Professor Martin Wegener of the Center for Functional Nanostructures (CFN) at the KIT are international experts in this field. Last year they managed to create this invisibility cloak effect three-dimensionally at a wavelength range of 1500 to 2600 nanometres, which is no longer visible but plays a role in telecommunications. Now two members of Wegener’s team, Joachim Fischer and Tolga Ergin, have refined the structure of the Karlsruhe invisibility cloak so that it can direct visible red light in the 700 nanometre wavelength range. In order to generate the required minute 3D structures in a polymer-air mixture, the KIT researchers used a process developed at the CFN known as direct laser writing, the resolution of which was improved using an “optical eraser”. Metamaterials endowed with such optical characteristics have the potential to facilitate innovations in optics, solar cell development, chip production and data transmission.

Antonia Rötger

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