Can 3D light localization be reached in ‘white paint’?

Abstract

When waves scatter multiple times in 3D random media, a disorder driven phase transition from diffusion to localization may occur (Anderson 1958 Phys. Rev. http://dx.doi.org/10.1103/PhysRev.109.1492 109 http://dx.doi.org/10.1103/PhysRev.109.1492 ; Abrahams et al 1979 Phys. Rev. Lett. http://dx.doi.org/10.1103/PhysRevLett.42.673 42 http://dx.doi.org/10.1103/PhysRevLett.42.673 ). In ‘ The question of classical localization: a theory of white paint? ’ Anderson suggested the possibility to observe light localization in TiO _2 samples (Anderson 1985 Phil. Mag. B http://dx.doi.org/10.1080/13642818508240619 52 http://dx.doi.org/10.1080/13642818508240619 ). We recently claimed the observation of localization effects measuring photon time of flight (ToF) distributions (Störzer et al 2006 Phys. Rev. Lett. http://dx.doi.org/10.1103/PhysRevLett.96.063904 96 http://dx.doi.org/10.1103/PhysRevLett.96.063904 ) and evaluating transmission profiles (TPs) (Sperling et al 2013 Nat. Photonics http://dx.doi.org/10.1038/nphoton.2012.313 7 http://dx.doi.org/10.1038/nphoton.2012.313 ) in such TiO _2 samples. Here we present a careful study of the long time tail of ToF distributions and the long time behavior of the TP width for very thin samples and different turbidities that questions the localization interpretation. We further show new data that allow an alternative consistent explanation of these previous data by a fluorescence process. An adapted diffusion model including an appropriate exponential fluorescence decay accounts for the shape of the ToF distributions and the TP width. These observations question whether the strong localization regime can be reached with visible light scattering in polydisperse TiO _2 samples, since the disorder parameter can hardly be increased any further in such a ‘white paint’ material.

Keywords

• Anderson localization of light
• fluorescence
• titania powder