September 13 2019, 11 AM

François AMBLARD, IBS Center for Soft and Living Matter Distinguished Professsor – UNIST – Ulsan National Institute for Science and Technology - Ulsan – South Korea

Lieu(x) :       Amphithéatre Cauchy, Ecole Polytechnique

Contact :    Antigoni Alexandrou
                    antigoni.alexandrou at polytechnique.edu

For a very broad class of objects, from small molecules and proteins to virtually any kind of soft matter, the analysis of thermal and non-thermal fluctuations plays an essential role for understanding their structure or their activity. In that context, various methods based on light scattering and interferences have proven essential for understanding a wide range of phenomena in nature. I will first illustrate how coherent multiple light scattering generates intensity speckles with fluctuations that reveal the conformational dynamics of the mechano-enzyme called myosin. Second, I will report on the creation of a new kind of optical field which corresponds to a photon gas with statistically uniform density, isotropic wave vectors and full depolarization. Unlike a thermal photon gas however, this field is produced by a single frequency light inside a highly reflecting Lambertian cavity, with maximal spatio-temporal coherence. I will demonstrate with experiments and theory, that the resulting 3D speckle field acts as a random interferometer. It strongly amplifies optical fluctuations and leads to pico-meter sensitivity over a 10-decades frequency range and a 4-decades signal dynamics. A few applications of this new concept of dynamic volume interferometry will be shown in biophysics, soft matter physics, and interferometry at large.

Download : Séminaire AMBLARD