Controlling light propagation in complex media : from mesoscopic effects to biomedical imaging

Sylvain Gigan (LKB-ENS) — October 1, 2015

Scattering of light in heterogeneous media, for instance the skin or a glass of milk, is usually considered an inevitable perturbation or even a nuisance. Through repeated scattering and interferences, this phenomenon seemingly destroys both the spatial and the 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 see its length greatly extended due to the multiplicity of possible path length light can take before exiting the medium. From an operative point of view, scattering greatly limits the possibility to image or manipulate an object with light through or in a scattering medium.
Multiple scattering is nonetheless an invaluable field of research for experimentalists and theoreticians alike, at the crossing of optics, condensed matter physics, statistical physics, chaos, to name just a few. The possibility of continuously varying the complexity of the structures from totally disordered (like suspensions in liquid) to ordered structures (like photonics crystals), from solid to granular or even liquid state, from simple scattering to resonant scattering, absorption, or even gain media, opens seemingly endless possibilities to investigate new physics phenomena.
Multiple scattering is a highly complex but nonetheless deterministic process : it is therefore reversible. Speckle is coherent, and can be coherently controlled and manipulated. By « shaping » or « adapting » the incident light, it is in principle possible to control the propagation and overcome the scattering process. I will present recent results from our group showing how light control allows not only imaging through or in a disordered medium, but also how we can unravel elusive or even new mesoscopic phenomena.

Biography :
Sylvain Gigan is currently professor at Université Pierre et Marie Curie, and researcher at Laboratoire Kastler-Brossel, at the Physics Department of ENS, where he leads the team “optical imaging in complex and biological media”. He is member of the institut Universitaire de France. He holds a PhD in quantum Optics under the direction of Claude Fabre, and has been successfully a postdoctoral researcher in quantum information in Vienna in the group of Markus Aspelmeyer, and associate professor at ESPCI ParisTech and institut Langevin.

You can also watch this video on the multimedia site ENS : savoirs.ens.fr