Shedding light on Anderson localization

Dec 20, 2012
This shows the diffusion of light in a disordered, cloudy medium at intervals of one nanosecond (= billionth of a second). After approximately four nanoseconds, the light can no longer spread any further in the medium. Credit: University of Zurich

Waves do not spread in a disordered medium if there is less than one wavelength between two defects. Physicists from the universities of Zurich and Constance have now proved Nobel Prize winner Philip W. Anderson's theory directly for the first time using the diffusion of light in a cloudy medium.

Light cannot spread in a in a cloudy medium like milk because the many of fat divert the light as defects. If the disorder – the concentration of defects – exceeds a certain level, the waves are no longer able to spread in a cloudy medium at all. Philip. W. Anderson was the first to describe this transition to a localized wave in 1958, which is why it is also referred to as Anderson localization. Until now, however, Anderson localization had never been observed. For the first time, physicists from the universities of Zurich and Constance have now demonstrated the Anderson localization of light directly in an experiment. As their article published in the science journal reveals, the Anderson localization of light only occurs in much cloudier media than milk – in other words, only if there is only about one between two defects.

Light propagation followed closely to a billionth of a second

For their study, the team examined the diffusion of light in a very strongly scattering medium. "In order to make the of the light and thus Anderson localization visible, pictures had to be taken at an interval of less than a billionth of a second," says Christof Aegerter, explaining the technical challenges of the project. Based on these high-resolution images, the researchers were able to show that in the case of Anderson localization light is no longer able to spread any further in the medium after around four billionths of a second (or nanoseconds).

Until now, it was very difficult to calculate certain characteristics of localized states, such as how large the critical concentration of the defects is. "Thanks to our experimental data, the theory will gain new impetus and be able to be refined further," Aegerter is convinced.

The Anderson localization of waves is a general phenomenon that occurs in all waves with a heavy scattering and is also of practical importance: It describes, among other things, the transition between a conductor and an isolator.

Explore further: The first direct-diode laser bright enough to cut and weld metal

More information: T. Sperling, W. Bührer, C. M. Aegerter, G. Maret. Direct determination of the transition to localization of light in three dimensions. Nature Photonics. DOI: 10.1038/NPHOTON.2012.313

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ValeriaT
not rated yet Dec 25, 2012
This subject may appear exotic and separated from reality for someone, but it's an analogy of stationary vortices formation at the surface of river, when the surface ripples are becoming too intensive. In dense aether model it's the mechanism in which the waves (bosons) materialize into massive particles (fermions). Note that Anderson was one of main authors of so-called Higgs mechanism (which is called more consequentially the ABEGHHK'tH mechanism [for Anderson, Brout, Englert, Guralnik, Hagen, Higgs, Kibble and 't Hooft])
ValeriaT
not rated yet Dec 25, 2012
the Anderson localization of light only occurs in much cloudier media than milk
In less dispersive medium the light indeed will not stop, but we can still observe it as so-called autofocusation of laser beams. It can be observed for intensive, but very short pulses of light. The general principle is, the refraction index of environment increases with intensity of light nonlinearly, when higher harmonic frequencies are generated. In such case the beam is behaving like the rod of more dense environment and it has a tendency to focus the light toward axis of beam into even more dense beam in avalanche-like mechanism, until it will close the light wave inside of spherical lens of plasma.