Sharper Focal Spot for a Radially Polarized Beam Using Ring Aperture with Phase Jump. (15th April 2013)

• Record Type: Journal Article
• Authors: Khonina, Svetlana N.; Ustinov, Andrei V.
• Other Names: Li You-Rong Academic Editor.
• Is Part Of: Journal of engineering. Volume 2013(2013)
• Publication Date: 2013-04-15
• Subjects: Engineering -- Periodicals; 620.005
• DOI: 10.1155/2013/512971
• Languages: English
• ISSNs: 2314-4904

Abstract

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= 0.33 λ ) 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.