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.
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 can be done by optimization methods, optical phase conjugation, or via the ability to measure the transmission matrix of a complex medium [1].
Linear fluorescence is at the same time one of the most simple and widespread optical imaging method, yet it remains a huge challenge for deep tissue imaging. I will show our recent results on focusing and imaging at depth on fluorescent objects using wavefront shaping in combination with matrix factorization and phase retrieval [2,3], but also show our recent results on functional fluorescence imaging WITHOUT shaping [4].
References:
[1] S. Rotter, S. Gigan, Rev. Mod. Phys. 89, 015005 (2017)
[2] A. Boniface, J. Dong, S. Gigan, arXiv:2003.04255
[3] A. Boniface, B. Blochet, J. Dong, S. Gigan Optica 6, 1381-1385 (2019)
[4] C. Moretti, S. Gigan Nature Photonics 14, 361 (2020)
Sylvain Gigan is Professor of Physics at Sorbonne Université in Paris, and group leader in Laboratoire Kastler-Brossel, at Ecole Normale Supérieure (ENS, Paris). His research interests range from fundamental investigations of light propagation in complex media, biomedical imaging, computational imaging, signal processing, to quantum optics and quantum information in complex media. He is also the cofounder of a spin-off: LightOn (www.lighton.ai) aiming at performing optical computing for machine learning and Big Data.
After graduating from Ecole Polytechnique (Palaiseau France) in 2000, and a Master Specialization in Optics from University Paris XI (Orsay, France), he obtained a PhD in Physics 2004 from University Pierre and Marie Curie (Paris, France) in quantum and non-linear Optics. From 2004 to 2007, he was a postdoctoral researcher in Vienna University (Austria), working on quantum optomechanics, in the group of Markus Aspelmeyer and Anton Zeilinger. from 2007 to 2014, he was at ESPCI ParisTech as Associate Professor, and started working on optical imaging in complex media and wavefront shaping techniques, at the Langevin Institute. He was awarded the Fabry de Gramont Prize of the French Optical Society in 2016, The Joseph Fourier ATOS prize in 2018, the Jean Jerphagnon Prize in 2019. He is the recipient of two ERC grants in 2011 and 2017. He is a member of the Institut Universitaire de France since 2016. He is Editor of Optics Communications.