Effect of annular obstruction and numerical aperture in the focal region of high NA objective lens

Abstract

In this article, based on the vector diffraction theory, the effect of annular apodization and numerical aperture in the focal region of tightly focused azimuthally polarized Bessel Gaussian beam by high NA lens is investigated numerically. The results show that our proposed system generates a longitudinally polarized beam in sub wavelength focal spot having large uniform focal depth of incident beam with annular aperture for lower NA. Such kind of subwavelength focal segment may find wide applications in optical traps, biological applications, atmospheric sciences and optical manipulation technology.