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. 109 1492–505; Abrahams et al 1979 Phys. Rev. Lett. 42 673–6). In ‘The question of classical localization: a theory of white paint?’ Anderson suggested the possibility to observe light localization in TiO2 samples (Anderson 1985 Phil. Mag. B 52 505–9). We recently claimed the observation of localization effects measuring photon time of flight (ToF) distributions (Störzer et al 2006 Phys. Rev. Lett. 96 063904) and evaluating transmission profiles (TPs) (Sperling et al 2013 Nat. Photonics 7 48–52) in such TiO2 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 TiO2 samples, since the disorder parameter can hardly be increased any further in such a ‘white paint’ material.
Highlights
The prediction of a disorder induced metal-insulator phase transition made by Anderson [1] and the generalization as a wave phenomenon [6] stimulated many theoretical and experimental studies over more than 50 years [7]
We showed in figure 2(a) a first crude spectral analysis of the ToF distribution for a sample consisting of R700 embedded in agarose
To test whether the measured fluorescent signal suffices to explain our old and new data, we extended the ToF intensity distribution I(t) and the time dependent width of the TP, both known from the diffusion theory [26, 35, 38], by including a fluorescence decay
Summary
T Sperling, L Schertel, M Ackermann, G J Aubry, C M Aegerter and G Maret. Any further distribution of this work must maintain suggested the possibility to observe light localization in TiO2 samples We recently claimed the observation of localization effects measuring photon time of flight the work, journal citation (ToF) distributions 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 TiO2 samples, since the disorder parameter can hardly be increased any further in such a ‘white paint’ material
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