Magneto-optical Faraday effect in multiple-scattering media

Abstract

When waves get multiply scattered in 3D random media, a disorder driven phase transition from diffusion to localization can be observed. This phase transition was fi rst predicted by P. W. Anderson for electronic systems [1]. For light waves, this transition was recently measured in 3D by Störzer et al. with time of flight measurements [2] and by Sperling et al. analyzing the 2D transmission pro file [3]. While the origin of Anderson localization is claimed to be the interference between time-reversed scattering paths, experimental evidence is still missing. The Faraday effect can be used to destroy time-reversal symmetry in multiple scattering media [4, 5]. To affect light localization by magnetic fields via the Faraday effect, disordered media that show both signs of localization and strong Faraday rotation has to be used. This thesis reports the characterization of a two component material made of a strongly scattering powder (TiO2) and a Faraday active powder (CeF3). The samples were characterized in a speckle interferometer regarding their degree of Faraday rotation. This was done by measuring the decay of the speckle intensity correlation function with increasing magnetic field, and comparing the experimental data with a theoretical description developed by F. Erbacher [6]. A time of flight setup was used to determine their light transport properties, namely the diffusion coeffcient and the absorption length, and the disorder parameter was characterized by measuring the coherent backscattering cone. The obtained results lead to the prediction that this two component material can be prepared to show the required properties for observing a magnetic field driven transition from light localization to diffusion. This would be an evidence that the origin of Anderson localization is the constructive interference on time-reversed scattering paths.