Saifollah RASOULI
(Inst. for Advanced Studies in Basic Sciences, Zanjan, Iran)

In this talk, a comprehensive theory for the diffraction of vortex beams from structured apertures especially from one- and two-dimensional (2D) periodic and quasi-periodic structures is introduced, and efficient robust and reliable diffraction-based methods for characterization and multiplication of the optical vortices are proposed. It is shown that in the diffraction of a vortex beam from 2D periodic structures having sinusoidal or Ronchi profiles, only for the odd values of the topological charge (TC) of the incident beam, the vortex beam is multiplied over an array at the Talbot planes of the structure, in which the TCs of all of the generated vortex beams are equal to one. It is also shown that when the opening number of the 2D binary grating is less than 1/2, for the both odd and even values of the TC of the incident beam, at the distinct Talbot planes, arrays of vortex beams having the same TC of the incident beam are generated. For this grating the former behavior is also observed but at different propagation distances. In addition, grating-based diffraction methods for generation of structured beams are introduced. The use of Fraunhofer diffraction patterns of almost-periodic structures for 3D multiple particles trapping is also proposed. Some experimentally multiple particles trapping and manipulation using the introduced methods are presented.