Regensburg 2004 – scientific programme
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SYPF: Physics of Foams
SYPF 2: Foams II
SYPF 2.1: Talk
Wednesday, March 10, 2004, 14:30–14:50, H16
The role of geometrical optics for light transport in dry foams — •Holger Stark1 and MirFaez Miri2 — 1Universität Konstanz, Fachbereich Physik, D-78457 Konstanz, Germany — 2Institute For Advanced Studies in Basic Sciences, Zanjan, Iran
Recent light-scattering experiments on foams suggest that the light transport is diffusive. This means that single photons can be considered as random walkers. However, there is a debate in literature about the main mechanism underlying the random walk. One suggestion is that it is based on light scattering from Plateau borders and/or vertices. On the other hand, since the cells are much larger than the wavelength of light, one can employ geometrical optics and follow a light beam or photon as it is reflected by the liquid films with a probability r called the intensity reflectance. This naturally leads to a random walk of the photons in space.
Here we study the second mechanism based on geometrical optics in two steps using numerical simulations. In a first model, we introduce topological and geometrical disorder based on a 2D Voronoi foam model and choose a constant r to investigate the influence of disorder. In a second model, we use the realistic intensity reflectance r of thin films and also consider disorder in the film thickness. Comparing our results to recent experiments, we find that the geometrical optics approach reproduces experimental features and the right order of magnitude for the diffusion constant. This convinces us that geometrical optics is an important mechanism for the diffusive light transport in foams.