Anomalous photon diffusion at the threshold of the Anderson localization transition

Microwave transmission through a random mixture of aluminum and Teflon spheres at a metal filling fraction of 0.30 is found to fall initially as 1/${\mathit{L}}^2$ in agreement with predictions of the scaling theory of localization. The renormalized diffusion coefficient is determined from measurements of transmission and of the spectral intensity correlation function. This function is found to be an expansion in ${\mathrm{\delta }}^{\mathrm{-}1}$, where δ is the product of the width and density of states in the medium. From these results we find the Ioffe-Regel criterion for photons to be ${\mathit{kl}}_{\mathit{c}}$=1.6±0.4.