Direct measurement of a radially polarized focused evanescent field facilitated by a single LCD

In this paper, a tightly focused evanescent field produced by a total internal reflection objective lens under the illumination of a radially polarized beam generated using a single liquid crystal phase modulator is investigated. The field distributions have been directly mapped by a scanning near-field optical microscope. It is demonstrated both theoretically and experimentally that the introduction of radially polarized beam illumination combining with an annular beam illumination exhibits advantages in two aspects. On one hand, it corrects the focus elongation and splitting in a focused evanescent field associated with a linearly polarized beam. On the other hand, it significantly improves the lateral localization to approximately a quarter of the illumination wavelength, which is less than half of the size that is achievable under linearly polarized illumination.