Novel material design for undistorted light waves

August 10, 2015
A wave penetrates a material: usually this leads to wave interference, to darker and brighter areas.

Materials that locally amplify or absorb light allow surprising new kinds of light waves – this has now been shown by calculations at TU Wien (Vienna).

When a light wave penetrates a material, it is usually changed drastically. Scattering and diffraction leads to a superposition of waves, resulting in a complicated pattern of darker and brighter light spots inside the material. In specially tailored high-tech materials, which can locally amplify or absorb light, such effects can be completely suppressed. Calculations at TU Wien (Vienna University of Technology) have now shown that these materials allow new kinds of , which have the same intensity everywhere inside the material, as if there was no wave interference at all. Due to their unusual properties, these new solutions of the wave equation could be useful for technological applications.

Obstacles Change the Wave

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 diffracted. At some points in space, the wave becomes brighter, in other places it becomes darker than it would have been without hitting the object. This is the reason we can see objects that do not emit light by themselves.

In recent years, however, experiments have been carried out with new materials which have the ability to modify light in a special way: they can locally amplify light, similar to a laser, or absorb light, like sunglasses do. "When such processes are possible, we have to employ a mathematical description of the light wave which is quite different from the one we use for normal, transparent materials," says Professor Stefan Rotter (TU Wien). "In this case we speak of non-hermitian media."

Specially designed non-hermitian materials remain completely unperturbed.

New Solutions for the Wave Equation

Konstantinos Makris and Stefan Rotter from TU Wien, together with Ziad Musslimani and Demetrios Christodoulides from Florida (USA), discovered that this alternative description allows new kinds of solutions for the wave equation. "The result is a light wave with the same brightness at each point in space, just like a wave in , even though it travels through a complex, highly structured material", says Konstantinos Makris. "In some sense, the material is completely invisible to the wave, even though the light passes through the material and interacts with it."

The new concept is reminiscent of so-called "meta-materials", which have been created in recent years. These materials have a special structure, which allows them to diffract light in unusual ways. In certain cases the structure can bend the light around the object, so that the object becomes invisible, much like Harry Potter's invisibility cloak. "The principle of our non-hermitian materials, however, is quite different", says Stefan Rotter. "The light wave is not bent around the object, but fully penetrates it. The way the material influences the wave is, however, fully cancelled by a carefully tuned interplay of amplification and absorption." In the end, the light wave is exactly as bright as it would have been without the object – at each and every point in space.

Several technical problems still have to be solved until such materials can be routinely fabricated, but scientists are already working on that. The theoretical work now published, however, shows that besides meta- there is another, extremely promising way to manipulate waves in unconventional ways. "With our work we have opened a door, behind which we expect to find a multitude of exciting new insights", says Konstantinos Makris.

Explore further: Particles, waves and ants

More information: "Constant-intensity waves and their modulation instability in non-Hermitian potentials." Nature Communications: dx.doi.org/10.1038/ncomms8257

Related Stories

Particles, waves and ants

November 26, 2014

Animals looking for food or light waves moving through turbid media – astonishing similarities have now been found between completely different phenomena.

Bringing back the magic in metamaterials

July 17, 2015

A single drop of blood is teeming with microorganisms—imagine if we could see them, and even nanometer-sized viruses, with the naked eye. That's a real possibility with what scientists call a "perfect lens." The lens hasn't ...

Laser physics upside down

July 15, 2014

At the Vienna University of Technology a system of coupled lasers has been created which exhibits truly paradoxical behaviour: An increase in energy supply switches the lasers off, reducing the energy can switch them on.

Two photons strongly coupled by glass fiber

November 2, 2014

Usually, light waves do not interact with each other. Coupling of photons with other photons is only possible with the help of special materials and very intense light. Scientists in Vienna have now created the strongest ...

Nanoparticles break the symmetry of light

October 6, 2014

How can a beam of light tell the difference between left and right? At the Vienna University of Technology (TU Wien) tiny particles have been coupled to a glass fibre. The particles emit light into the fibre in such a way ...

Engineers give invisibility cloaks a slimmer design

July 7, 2015

Researchers have developed a new design for a cloaking device that overcomes some of the limitations of existing "invisibility cloaks." In a new study, electrical engineers at the University of California, San Diego have ...

Recommended for you

How the Earth stops high-energy neutrinos in their tracks

November 22, 2017

Neutrinos are abundant subatomic particles that are famous for passing through anything and everything, only very rarely interacting with matter. About 100 trillion neutrinos pass through your body every second. Now, scientists ...

Quantum internet goes hybrid

November 22, 2017

In a recent study published in Nature, ICFO researchers led by ICREA Prof. Hugues de Riedmatten report an elementary "hybrid" quantum network link and demonstrate photonic quantum communication between two distinct quantum ...

Enhancing the quantum sensing capabilities of diamond

November 22, 2017

Researchers have discovered that dense ensembles of quantum spins can be created in diamond with high resolution using an electron microscopes, paving the way for enhanced sensors and resources for quantum technologies.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.