Grand Séminaire d'Institut

Vendredi 27 Octobre 2017 à 11h00.

Microspectroscopy of complex systems: limits and solutions via spatial light modulators

''Nonlinear optical processes are powerful approaches for probing complex soft matter systems (colloidal systems, biological specimens etc). For instance, by exploiting the intrinsic vibrational spectra of molecules, Coherent Raman Scattering processes offer unique capabilities such as high chemical selectivity imaging with video-rate speeds. Nevertheless, there still exists bottlenecks that hinder applications of nonlinear microspectroscopy for realistic complex scattering systems, such as biological tissues. In particular, (i) the penetration depth in biological tissues is remarkably shallow [1], and (ii) the datasets generated in vibrational microspectroscopy are overwhelmingly large [2]. In this presentation, I will introduce the problem involved in these current limitations, and also present our recent results aiming at lowering these barriers. At the heart of these solutions is the spatial light modulator, a device that enables active addressing of various degrees of freedom of light fields (spatial, spectral, polarization) in phase, and/or amplitude. To increase the penetration depth, I will introduce the recently developed field of wavefront shaping [3], which borrows concepts originally developed in mesoscopic physics. These concepts are the cornerstone for manipulating multiply scattered light aiming at increasing penetration depth, as we have recently demonstrated ~104 enhancement of nonlinear signals after a scattering medium [4]. To address the overwhelming datasets generated in microspectroscopy, I will introduce a new strategy that is based on concepts of compressive sensing. With this recently developed approach, one can enable spectroscopic acquisition in Stimulated Raman Scattering [5], and also higher sensitivity in the inexpensive spontaneous Raman microspectroscopy [6]. [1] S. Gigan, Nat. Phot. 11, 14-16, 2017; [2] C. H. Camp Jr. and M. T. Cicerone, Nat. Phot. 9, 295-305, 2015; [3] I. M. Vellekoop and A. P. Mosk, Opt. Lett. 32, 2309-2311, 2007; S. M. Popoff et al., Phys. Rev. Lett. 104, 100601, 2010; [4] H. B. de Aguiar, et al., Phys. Rev. A 94, 043830, 2016; [5] P. Berto et al., Opt. Lett. 42, 1696-1699, 2017; [6] P. Refregier et al., submitted; C. Scotte et al., “Precision of Raman compressed detection microspectroscopy”, in preparation''