Tighter focusing of amplitude modulated radially polarized vector beams in ultra-high numerical aperture lens systems

Abstract

Two kinds of amplitude apodization filters are proposed to modulate the radially polarized vector beam in ultra-high numerical aperture (NA) aplanatic lens systems in order to create a tighter focus. When focusing a radially polarized Bessel–Gaussian vector beam, we show the light spot at the focal plane is possible to be suppressed from 0.68λ to 0.46λ (32.4% sharper) with a dry objective lens of NA=0.95, and from 0.50λ to 0.34λ (32.0% sharper) with an oil immersion objective lens of NA=1.4, respectively; both surpass the Abbe's diffraction resolution limit of λ/(2NA). For a uniform radially polarized beam, the focal spot further sharpens.