The creation-annihilation process of phase singularities of flat-topped beams in the focal plane

The creation-annihilation process of phase singularities of flat-topped beams in the focal plane is studied within the framework of the scalar paraxial approximation, where the new expression for flat-topped beams introduced by Li is taken as the beam model. It is shown that by suitably varying the truncation parameter, the phase singularities reorganize themselves, which leads to the annihilation of singularities in the focal plane, the creation of singularities outside the focal plane and subwavelength structures. Apart from the truncation parameter, the beam order of flat-topped beams additionally affects the spatial distribution of phase singularities. (C) 2006 Elsevier GmbH. All rights reserved.