Numerical study of effects of light polarization, scatterer sizes and orientations on near-field coherent anti-Stokes Raman scattering microscopy.

We employ the finite-difference time-domain (FDTD) technique as a numerical approach to studying the effects of polarization, scatterers' sizes and orientations on near-field coherent anti-Stokes Raman scattering (CARS) microscopy imaging. The results show that to acquire better image contrast and larger near-field CARS signals, the scatterers with diameters of less than three-eighths of the pump field wavelength (lambda(p)) are preferable to be oriented along the polarization direction of the excitation light fields. It is also found that when the scatterers' sizes are smaller than half a wavelength of the pump field, the perpendicular polarization component of the induced near-field CARS radiations is strictly confined within the regions at the scatterer-water interface or the subsurface of scatterers, yielding a high image contrast (up to 200) with a spatial resolution of lambda(p)/16. This study indicates that perpendicular polarization components of near-field CARS microscopy could be used to uncover very fine structures of intra- and/or inter- cellular organelles in cells with nanoscale resolutions.