Study on Focusing Mechanism of Radial Polarization with Immersion Objective

In this study, we employ vectorial diffraction to examine the focusing mechanism of radially polarized beams using an immersion objective with linear and circular polarized illuminations. Radial polarization features a sharp focus in a high-numerical-aperture (NA) system. The longitudinal component governing spot formation depends on the bending of the polarization vector rather than the immersion circumstance. As the marginal angle of the objective exceeds 64.16 and 71.81°, the depolarization effect of the radially polarized beam enables a smaller spot than the linear and circular polarizations, respectively.