Coherent anti-Stokes Raman scattering (RP-CARS) microscopy for sensing molecular orientations

We report coherent anti-Stokes Raman scattering (CARS) microscopy with radially polarized (RP) excitation for facilitating longitudinally oriented molecules detection. Our finite-difference time-domain (FDTD) simulation results show that the maximum near-field RP-CARS radiation from the two longitudinally orientated nanoparticles is around 1.3 times higher than that from transversely orientated nanoparticles. Our further CARS experiments show that RP-CARS radiation from molecules oriented along the longitudinal direction is approximately 3-fold stronger than that using linearly polarized CARS technique, and the lateral resolution of RP-CARS imaging can be improved by about 10% compared to the linearly polarized CARS imaging.