Light Beam Observation Expands Beyond the Disturbance Spectrum | Research & Technology | June 2022
ROSTOCK, Germany, June 14, 2022 – Researchers from the University of Rostock and the Technion – Israel Institute of Technology have demonstrated a mechanism that prevents light waves from traveling freely. The underlying physical effect was previously thought to be too weak to completely stop wave expansion. The researchers observed that such localization of light was nevertheless possible, demonstrating the sensitivity of wave propagation over a wide range of spatial length scales.
In 1958, physicist Phil Anderson predicted that an electrical conductor, like copper, could suddenly turn into an insulator, like glass, when the order of atomic crystals was changed enough. The presence of this so-called disorder could stop the movement of otherwise free-moving electrons, preventing any substantial electrical current through the material. The phenomenon is called Anderson localization, and it can be explained by quantum mechanics, in which electrons are treated as particles as well as waves.
The effect also applies to classic settings, where clutter can suppress the propagation of sound waves and light beams.
In recent work, researchers have found that light waves can even show that Anderson localization is induced if the disorder is virtually invisible to them. This type of disorder exclusively contains spatially periodic distributions with certain wavelengths.
“Naïvely, one would expect that only waves whose spatial distributions somehow match the length scales of the disorder would be affected and potentially know Anderson’s location,” said Sebastian Weidemann, PhD student at the Institute of Physics of the University of Rostock.
“Other waves should basically propagate as if there were no disorder,” said researcher Mark Kremer.
In contrast, recent theoretical work by the Technion team has suggested that wave propagation could be significantly affected even by such “invisible” disorder.
“When light waves can interact with the invisible cloud multiple times, a surprisingly strong effect can build up and stop all light propagation,” said PhD student Alex Dikopoltsev.
Laser light trapped in an invisible trap. Light travels in coupled optical fibers. Even though the disorder (not shown) should not affect the light waves, propagation into neighboring optical fibers strongly suppressed Anderson localization, so the light remained contained within a few optical fibers. The fiber mesh structure allows light to mimic the movement of electrons in disordered materials. Courtesy of A. Szameit/Rostock University.
The collaborating research groups constructed artificial disordered materials from miles of optical fiber, which they arranged in such a way that the optical gratings mimic the spatial propagation of electrons in the disordered materials. This allowed the researchers to make direct observations of the nearly invisible structures capturing the light waves.
According to the researchers, the demonstration and discovery could pave the way for a new generation of synthetic materials that harness disorder to selectively suppress currents – whether light, sound or electrons.
The Deutsche Forschungsgemeinschaft, the European Research Council and the Alfried Krupp von Bohlen und Halbach Foundation supported the work.
The research has been published in Scientists progress (www.science.org/doi/10.1126/sciadv.abn7769).