Fast polarization imaging in coherent Raman scattering for the observation of lipid order dynamics in real-time

Polarization resolved coherent Raman scattering (polar-CRS) provides information on molecular orientational organization, with the strong advantages of being a label free and chemically specific imaging method. Polarization tuning imposes however slow imaging acquisition rates. Here we demonstrate two strategies to fasten polarization resolved CRS and reach real time capabilities. First, fast polar-CRS imaging is obtained by a combined electro-optic polarization and acousto-optic amplitude modulations, applicable to both Stimulated Raman Scattering (SRS) and Coherent anti-Stokes Raman Scattering (CARS) point scanning imaging. The proposed scheme increases the speed of orientational imaging by two orders of magnitude as compared to polarization tuning approaches, and does not require post processing analyzes. Second, a combination of circular-based polarizations is used to directly filter the organization components of the probed samples, benefiting from symmetry matching properties between light and molecular assemblies. We demonstrate the potential of those methods for sub-second time scale imaging of lipid order packing and local lipid membrane deformations in artificial lipid multilayers, single cell ghosts, and myelin-rich tissues from spinal cords in live mice. Notably, these images permit to extract molecular scale signatures that bring for instance new information on the early stage of the development of neurodegenerative diseases.