Highly longitudinally polarized coherent anti-Stokes Raman scattering microscopy with improved spatial resolution

We proposed a method to enhance the longitudinally polarized component and improve the spatial resolution of radially polarized coherent anti-Stokes Raman scattering (CARS) microscopy by phase modulation. A specially designed phase pattern is applied onto the pump beam to suppress the radially polarized field component at the focal region. With this modulation, the calculated intensity ratio between the longitudinally and radially polarized CARS field is increased from 2.57 to 14.7, and the simulation of CARS imaging on a 120 nm polystyrene bead shows more than 3-fold spatial resolution improvement for both forward and backward detection. It is expected that this method could also be applied to other nonlinear optical imaging modalities for enhancing the longitudinally polarized component.