Theoretical Materials 'Invisible' to Light Waves

Materials that allow light to pass through without distortion are possible, according to a new set of calculations by an international team of researchers.

When a light wave travels through free space, its intensity can be the same everywhere. But as soon as it hits an obstacle, the wave is altered. Scattering and diffraction lead to a superposition of waves, resulting in a complicated pattern of darker and brighter light spots inside the material.

Interference usually results when a wave penetrates a material (top). Waves passing through specially designed non-Hermitian materials, however, remain completely unperturbed. Courtesy of TU Wien.

Specially tailored materials that locally amplify or absorb light could completely suppress such effects.

"The result is a light wave with the same brightness at each point in space, just like a wave in free space, even though it travels through a complex, highly structured material," said Konstantinos Makris, a postdoctoral fellow at the Vienna University of Technology (TU Wien). "In some sense, the material is completely invisible to the wave, even though the light passes through the material and interacts with it."

This proposed class of "non-Hermitian" materials differs from metamaterials, which have special structures that allow them to diffract light in unusual ways.

"The light wave is not bent around the object but fully penetrates it," said TU Wien professor Stefan Rotter. "The way the material influences the wave is, however, fully cancelled by a carefully tuned interplay of amplification and absorption."

The theoretical work was published in Nature Communications (doi: 10.1038/ncomms8257; open access version available at http://arxiv.org/abs/1503.08986).

For more information, visit www.tuwien.ac.at.