Elliptically polarized coherent anti-Stokes Raman scattering microscopy

We report an approach to coherent anti-Stokes Raman scattering (CARS) microscopy that significantly suppresses the nonresonant background for high-contrast vibrational imaging. We employ an elliptically polarized pump field with an aspect ratio of 1 : √3 of the ellipse combined with a linearly polarized Stokes field for elliptically polarized CARS (EP-CARS) microscopy. The EP-CARS technique yields a 6-7-fold improvement in signal-to-background ratios compared with normal CARS, while providing an approximately 1.25-fold improvement in resonant CARS signal compared with normal polarization-sensitive CARS microscopy. We demonstrate this technique by imaging 1.5 μm polystyrene beads in water and lipid droplets in unstained fibroblast cells.