What are the books on metamaterials

Metamaterial makes light dance

A kind of tiny innerspring mattress made of nanometer-sized gold spirals causes such a sensation that its discoverers are even celebrated as a highlight in the journal “Science”. The special thing about this new metamaterial: It polarizes the electrical and magnetic components of light in a particularly wide frequency range and thus opens up new applications.

Metamaterials have properties that are not found in nature. They can be used to manipulate electromagnetic waves, including light, in new ways. They consist of similar, regularly arranged elements which, although significantly larger than atoms in a crystal, interact with electromagnetic waves like these. Metamaterials produced using nanotechnological methods consist of such small units that they can influence electromagnetic waves with wavelengths from visible to infrared light.

These properties have sparked the imagination - and the urge to research - of scientists for a number of years. Perfect lenses without aberrations, even optical camouflage cloaks à la Harry Potter are theoretically possible. Scientists at the Karlsruhe Institute of Technology (KIT) are now for the first time describing three-dimensional metamaterials that could actually be used in spectroscopic measuring devices.

In the work that the respected journal Science published as a “highlight” on its website before it was printed, the team led by Professor Martin Wegener from the Center for Functional Nanostructures and Professor Volker Saile from the Institute for Microstructure Technology combined

different technologies.

Mattress made of gold spirals on a nanoscale

For the production of the new elements, the structure is "written" as it were with a laser in a photoresist and then dissolved. In a second step, the researchers galvanically deposit gold in the cavities created in the process until they are filled. Finally, they etch away the original polymer form. What remains is a structure that is reminiscent of a spring mattress: It consists of many regularly arranged, tiny gold spirals with a diameter of only a few hundred nanometers.

"The spirals bring light that shines through the metamaterial, as it were, the orderly waltz dancing," Wegener describes the functionality. Due to their structure, the three-dimensional metamaterials only allow one of the two directions of rotation of an electromagnetic wave to pass. They act as a filter for circularly polarized light.

Principle of galvanic gold deposition: Gold complexes dissolved in the electrolyte diffuse into the cavities of the structure, where they are decomposed at the cathode. The resulting gold ions are deposited and finally fill the cavities completely. © KIT

Wider frequency spectrum than previous metamaterials

This property is based on the fact that metamaterials directly influence not only the electrical but also the magnetic component of an electromagnetic wave. "Depending on the size of the spirals, such structures can do this for very different wavelengths and over a comparatively large range of wavelengths," explains Justyna Gansel from the Wegener group. Their results clear the previously observed disadvantage of metamaterials

from the fact that their special properties are only limited to a narrow frequency spectrum.

The novel compact and broadband circular polarizers could be of great interest for numerous applications in optical spectroscopy. For example, they could be built into handy devices that analyze mixtures of substances which themselves act as polarizers. "The right-turning lactic acids in yoghurt could be determined with the help of metamaterials in the future," speculates Gansel.

(Karlsruhe Institute of Technology, August 26, 2009 - NPO)

August 26, 2009