Speckle decorrelation with wavelength shift as a simple way to image transport mean free path

We present an experimental scheme for determining the light transport properties of random disordered materials. The sample is illuminated with a laser and the speckle patterns obtained at different wavelengths are recorded with a camera. The transport mean free path is then deduced from the correlation functions of the scattered intensities. This method is tested on two kinds of random materials: colloidal particles dispersed into a polymeric matrix and on granular material made of glass beads. The possibility to image a material with a disorder varying at large scale is finally presented.