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Résumé |
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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