Scattering of coherent light in heterogeneous biological media and tissues , leads to strong scattering and interferences phenomena which destroy both the spatial amplitude and phase information of any laser illumination. At the spatial level, it gives rise to the well-known “speckle” interference patterns. At the temporal (or spectral) level, a short pulse entering a scattering medium will be stretched due to the multiplicity of path lengths in the propagating medium. Consequently this greatly limits the imaging of an object through a scattering medium. Multiple scattering is a highly complex but nonetheless deterministic process: it is therefore reversible, in the absence of absorption. Speckle can be coherently controlled. By “shaping” or “adapting” the incident wavefront, it is in principle possible to control the propagation and to overcome the scattering process. Liquid crystal spatial light modulator (SLM) is a tool of choice to shape a laser beam over a very large number of modes, in order to match the high complexity of a multiple scattering medium. I will show how, using a SLM, one can measure the transmission matrix which links the input – output modes of the scattering medium. We present our original approach of solving the inverse problem for the reconstruction of an arbitrary image through the scattering media. I will detail our recent experiments with phase SLMs applied to, spatial focusing, imaging and phase conjugation through a thick opaque multiple scattering media. Beyond the spatial aspects of wave control, I will also review the recent progress on temporal control in complex media and its interests for mesoscopic physics studies.

Institut Langevin, CNRS and ESPCI ParisTech