Label-free super-resolution stimulated Raman scattering using 4Pi-SRS

Super-resolution has enabled new investigations into biological nanostructures smaller than the diffraction limit of light. Compared to the wide variety of super-resolution fluorescence microscopy techniques, label-free super-resolution chemical imaging has proven to be much more challenging due to its lower sensitivity. Multiple studies such as saturation-based methods, VISTA, and APoD-SRS enable label-free super-resolution, each with limitations. In this work, by combining stimulated Raman scattering (SRS) and 4Pi-interferometry, we present a 4Pi-SRS microscopy system that improves the axial resolution nearly 7-fold. We report the characterization of the 4Pi-SRS microscope resolution with 80 nm polystyrene beads.