Pr. Sylvain Gigan
LKB, ENS Paris
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Light In complex Media: from imaging to computing
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 andthe 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 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. This concept has been exploited in the last decade to focus and image through and in complex media, and opens important prospects for imaging at depth in biological media. I will present some recent work from the group illustrating this possibility, focusing on non-invasive fluorescence imaging, and leveraging computational imaging concepts. I will also show how the random mixing induced by the propagation of light through a complex medium can be leveraged for various computational tasks, allowing the intriguing concept of computing with disorder.
