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Spatio-temporal control of light in complex media
Sébastien Popoff, doctorant. Crédits : ESPCI ParisTechThe aim of the work presented in this dissertation is to combine the tools and the formalism developed initially for acoustic waves with techniques peculiar to the field of optics.
The recent technology breakthroughs devoted to the spatial and temporal control and measure of the complex optical field have made possible these studies. Thanks to a system that allows us to spatially control and measure the optical field, we record the transmission matrix of a diffusing medium. We exploit this matrix to focus light and detect an image through the medium. We also apply the analysis of the matrix to the study of some physical properties of the medium. Using the same model and a similar experimental setup, we then measure through an aberrating medium the reflection matrix of a system that consists of a few strong scatterers. Using the singular value decomposition of this matrix, we are able to detect and selectively focus light on the scatterers, compensating in the process the aberrations induced by the propagation medium. Another approach described is to apply the analysis of the reflection matrix to study the radiation patterns of a unique scatterer. The last study concerns the application of the time reversal technique with modulated signals in optics. This method consists in recording the response of a medium to a modulation. These responses are then exploited to focus light inside the medium.
We successfully prove the efficiency of this technique for a temporal focusing experiment in an optical cavity. We then try to extend these results to spatio-temporal focusing.
Keywords : optics, scattering, phase conjugation, time reversal, focusing, imaging