Effect of numerical aperture on the spectral splitting feature near phase singularities of focused waves

Effect of numerical aperture (NA) on the spectral splitting feature near phase singularities of focused waves was analyzed. The spectral splitting feature near the maximum-intensity points under polychromatic illumination existed neither in the incident polarization direction nor in the axial direction. A critical NA value in the incident polarization direction was found to be small as 0.05.