Breakdown of di usion approximation for light propagation in nano-porous GaP sponges
| Abstract | Highly-scattering materials have been the subject of research for morethan a hundred years, but the enthusiasm in the subject has neverdeclined. Most of the observed phenomena have been described within thephoton di usion approximation. The di usion approximation will breakdown in the extreme case where interference e ects become so signi cantthat a phase transition to Anderson localization regime happens.Nano-porous GaP sponges are of particular interest for the observationof this transition. In this thesis both stationary and non-stationarymeasurements on Nano-porous GaP are presented. A new experimental methodis proposed and introduced as the e usion microscopy. This method isshown to give valuable information about the e ect of anisotropicdi usion as well as non-di usive behaviors. E usion microscopy hasrevealed that a few of our samples deviate from the di usive regime, andpossibly show signs of Anderson localization. Second-harmonic generationin nano-porous GaP slabs has also been studied experimentally. Totalsecond-harmonic yield measurements and the ratio of second-harmoniclight emitted from the front and back side of the sample were comparedwith the theoretical predictions of the non-stationary di usionapproximation. It has been shown that most of the samples show behaviorconsistent with the photon diff usion model. However, a subset of thesamples deviate up to a factor of 10 times from diff usive behavior.These cases are highlighted and the connection to the Andersonlocalization of light is expressed. |
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| Authors | S. Faez, |
| Year of publication | 2007 |
| Date published | 06/2007 |
| School | University of Twente |
| Keywords |