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-pi phase plate, an ultra small dark spot regardless of side-lobe intensity is generated with main-lobe peak to peak distance shrunk to 0.24 lambda, 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. (C) 2015 Elsevier B.V. All rights reserved.
Science & Technology
; Physical Sciences
DIFFRACTIVE SUPERRESOLUTION ELEMENTS
; DOUGHNUT FOCAL SPOT
; STED MICROSCOPY