Optical experiments on germanium powders close to the Anderson localization transition

J. Gomez Rivas, R. Sprik, and A. Lagendijk, Van der Waals Zeeman Instituut, Universiteit van Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands. C.W. Rella and L.D. Noordam, FOM-Institute for Atomic and Molecular Physics (AMOLF), Kruislaan 407, 1098 SJ Amsterdam, The Netherlands.

We present mid-infrared optical transmission and reflection measurements in slabs of randomly packed germanium micron size particles. Germanium has a very high refractive index in the mid-infrared, being a good candidate to prepare a material in which light is localized. Using a free electron laser as light source, we have studied the wavelength dependence of the scattering properties and the optical absorption. Our samples are very close to the localization transition. The scattering mean free path is obtained from the transmitted fraction of the coherent beam. The total transmission and reflection measurements give the transport mean free path and the absorption length. A transport mean free path smaller than the scattering mean free path is a signature of interference effects at the proximity of the localization transition.