Modelling light transport in dry foams by a coarse-grained persistent random walk

A two-dimensional persistence random walk model with two states is considered. In the immobile state, the particle chooses a new direction according to some probability function, while in the mobile state it persists on its direction and performs a ballistic motion. Starting from a master equation, we are able to calculate the diffusion constant for this model. The model was developed to explain Monte Carlo simulations of photon diffusion in two-dimensional dry foams. While it gives the leading term in the diffusion constant D, it fails to reproduce the details in D which depend on the amount of disorder in foams. This might show that diffusing photons probe local structural correlations in foams