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Journal of Engineering
Volume 2013, Article ID 512971, 8 pages
http://dx.doi.org/10.1155/2013/512971
Research Article

Sharper Focal Spot for a Radially Polarized Beam Using Ring Aperture with Phase Jump

Image Processing Systems Institute of the Russian Academy of Sciences, Molodogvardeiskaya Street 151, Samara 443001, Russia

Received 28 November 2012; Revised 4 March 2013; Accepted 10 March 2013

Academic Editor: You-Rong Li

Copyright © 2013 Svetlana N. Khonina and Andrei V. Ustinov. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We study analytically and numerically in which way the width of ring aperture containing a phase jump affects the size and intensity of the focal spot generated with a radially polarized beam. It is shown that by means of destructive interference of beams coming from the different-phase rings it becomes possible to overcome the scalar diffraction limit corresponding to the first zero of the zero-order Bessel function. The minimal focal spot size (FWHM ) is found to be attained when the annular aperture width amounts to 20% of the full-aperture radius. In this case, the side-lobe intensity is not larger than 30% of the central peak. A wider annular aperture with the phase jump introduced is also shown to form a focal spot not exceeding the diffraction limit for a narrow annular aperture, simultaneously providing a nearly six times higher intensity. In this case, the side lobes amount to 35% of the central peak.