Optical Transmission Through Strong Scattering and Highly Polydisperse Media
Anderson localization refers to a break-down of the wave propagation in disordered scattering systems due to interference. As localization is essentially a wave phenomenon it should hold for all kind of waves i.e. electrons, electromagnetic and acoustic waves. For isotropic scatterers localization is established if kl s ≤ 1, where k is the wavevector in the medium and l s is the scattering mean free path. To approach the localization transition, l s can be reduced by using scatterers with a high refractive index, n, and a size such that the scattering cross section is maximal. An interesting class of materials are semiconductors that have very large refractive indexes and almost not absorption for wavelengths well below the energy of the band gap. Recently localization of light has been observed in GaAs powders , opening the possibility to new studies in this field. We investigate the infrared transmission through samples of randomly packed silicon powders. In the wavelength range 1.4μm to 2.5μm we analyze in detail the scattering properties and the effects of residual absorption. In this range we observe a nearly constant value of kl s around 3.5. We attribute the non-variation of kl s with the wavelength to the high polydispersity in the size of the Si particles. Due to the similar refractive indexes of GaAs and Si, it is surprising that we do not observe Anderson localization in the Si samples. An explanation could be a difference in the connectivity of the particles.