Rémi Carminati, Institut d’Optique Graduate School

Résumé : Multiple scattering of light in disordered media has been an active field for many years, driven by applications to sensing and imaging with diffuse light, and by fundamental questions in wave transport in complex environments. Multiple scattering in the presence of nonlinearities has emerged as a new branch in the field, that had remained largely unexplored until recently.
In the talk we will described recent advances in the understanding of second harmonic generation (SHG) in random media (powders) [1,2]. We will analyze the building of the second-harmonic diffuse intensity in space and time, thus providing a simple theoretical basis to the concept of random quasi-phase matching.
We will also discuss another type of nonlinearity, when a the optical properties of a medium that vary randomly in time [3-5]. Time-varying materials or metasurfaces have been proposed recently has promising tools for the control of electromagnetic or acoustic waves. Here we will focus on features emerging from random time modulations. For example we will show that instabilities in the wave field lead to an exponential growth of the wave energy at long times.