Pantheon SEMPARIS Le serveur des séminaires parisiens Paris

Status Confirmed
Seminar Series SEM-PHYS-ENS
Subjects physics.optics
Date Tuesday 19 September 2017
Time 17:15
Institute DPT-PHYS-ENS
Seminar Room room Conf. IV, 24 Rue Lhomond, ENS Paris
Speaker's Last Name Gigan
Speaker's First Name Sylvain
Speaker's Email Address
Speaker's Institution LKB
Title Departmental Lecture 2/2: Light Control in complex media: from imaging to mesoscopic physics... and back
Abstract 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 and 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. Multiple scattering is a highly complex but nonetheless deterministic process: it is therefore reversible, in the absence of absorption : speckle is coherent, and can be coherently controlled. By « shaping » or « adapting » the incident light, it is in principle possible to control the propagation and overcome the scattering process. The central tool that we exploit is the ability to measure the transmission matrix of a complex medium. In the first lecture, I will first details the basics of light scattering and disordered media, and then show how the concept of wavefront shaping has opened tremendous prospects for optical imaging through and in complex media. In the second lecture, I will come back the the physics of waves in disordered system, and detail the various mesoscopic effects (open and closed channels, memory effect, ...) that can arise. I will show how the wavefront shaping tools can be used to unravel some of these effects in optics, and in turn how these effects can sometimes be exploited for imaging.
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