Static and dynamic transport of light close to the Anderson localization transition - art. no. 046613

Anderson localization of light refers to an inhibition of wave transport in scattering media due to the interference of multiple scattered waves. We p resent wavelength dependent midinfrared optical transport measurements in s labs of randomly packed germanium (Ce) micron-sized particles, using a free electron laser as a tunable source of pulsed radiation. Because of their h igh refractive index and low absorption, Ge and similar semiconductors are excellent systems td study Anderson localization of light. To characterize the samples fully, we have employed several complementary optical technique s: total diffuse transmission, total diffuse reflection, coherent transmiss ion, and time-resolved speckle interferometry. In this way we obtained the scattering (l(s)) and transport (l) mean free paths, the absorption coeffic ient (alpha), the diffusion constant (D), and the energy transport velocity (v(e)). These- measurements have been made as a function of midinfrared wa velength, so that the scattering cross section:and absorption coefficients can be Vaned in the same samples. We found that the Ge samples are close (k l(s)approximate to3) to the localization transition, but still above it. Ou r measurements of l(s) and l suggest that l is renormalized due to interfer ence at the proximity of the localization transition. We also found that th e diffusion constant is significantly reduced in samples thinner than appro ximate to 7l.