Polarization-coded coherent anti-Stokes Raman scattering microscopy for nonresonant background suppression

Abstract

The existence of non-resonant background severely decreases the image contrast and may overwhelm the resonant signal from small scatterers in coherent anti-Stokes Raman scattering (CARS) microscopy. In this study, we found that by using circularly polarized pump and Stokes excitations with inverse rotation directions, the non-resonant as well as the resonant CARS generation from molecules with symmetry can be totally suppressed, whereas the resonant CARS signal from asymmetric molecules preserves. This unique property of circularly polarized CARS is useful for high-contrast imaging of asymmetric samples without the interference of non-resonant background, which is demonstrated by the imaging of natural silk fibers. © 2013 SPIE.