Large scale manipulation of the dark spot by phase modulation of azimuthally polarized light

A new method is proposed to focus azimuthally polarized beam into an ultra-small or ultra-big dark spot under high numerical aperture lens system. Manipulated by proper designed binary 0-π phase plate, an ultra small dark spot regardless of side-lobe intensity is generated with main-lobe peak to peak distance shrunk to 0.24λ, which is 46% of the case without phase plate. For potential applications, shrinking the dark spot and suppressing the side-lobe intensity are analyzed, and several cases of squeezed dark spots with different levels of side-lobe intensities are presented. Additionally, using a two-zone phase plate to enlarge the dark spot is investigated in this paper, and an enlarged dark spot is readily acquired with the main-lobe peak to peak distance in a range of 100%-200%. The advantages of this method are its large scale manipulation of the dark spot size and its high performance in suppressing side-lobe intensity, which is of great worth in enhancing the performance of many systems such as optical tweezers and stimulated emission depletion (STED) microscope.