Tuesday, July 5, 2022

New type of physical effect that prevents light waves from propagating spatially

The light caught in invisible chains.

In collaboration with the Technion, the Israeli Institute for technology, physicists from the University of Rostock have offered the first experimental evidence of a new physical effect that prevents light waves from propagating spatially. They showed that structures almost invisible to light could also dramatically impact the propagation of light waves.

In 1958, P. W. Anderson came up with a famous phenomenon called Anderson Localization, both analytically and numerically. He demonstrated that an electrical conductor such as copper could suddenly behave like an insulator if the atomic lattice order is disturbed enough. Such a “disorder” can suddenly hold (“localize”) the otherwise freely moving electrons in place – and thus prevent any current flow.

However, this phenomenon could only be explained with the help of modern quantum physics– in which electrons are considered not only as particles but also as waves at the same time.

In this new study, physicists deal with the properties of light and its interaction with matter. They also discovered that light waves could be stopped by a new type of disorder that is practically invisible to the waves.

This disorder goes well beyond Anderson localization as it strongly favors certain spatially periodic distributions.

Sebastian Weidemann, a doctoral student at the Rostock Institute of Physics in Szameit’s group, said, “Previously it was thought that only those waves can be influenced (and therefore show an Anderson localization) whose spatial structures match the spatial distribution of the disorder.”

Dr. Mark Kremer, also from the group around Professor Szameit, said, “Other waves, on the other hand, spread almost undisturbed.”

Weidemann said“We designed and carried out an experiment that demonstrates this effect for the first time. We could see that light waves are limited to small spatial areas even if the disorder is supposed to be practically invisible to them.”

“For the experiment, we created the disordered structures artificially in the laboratory by connecting kilometers of optical glass fibers so that the propagation of light in these fibers imitates the movement of electrons in disordered materials.”

The discoveries are an essential step in basic research into wave propagation in disordered systems and potentially form the basis for further technical applications in which disorder can selectively suppress currents – whether for light, sound, or electrons.

Journal Reference:

  1. A. Dikopoltsev, S. Weidemann, M. Kremer, et al. Observation of Anderson localization beyond the spectrum of the disorder. DOI: 10.1126/sciadv.abn7769

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