Azimuthal phase-shifted zone plates to produce petal-like beams and ring lattice structures

Abstract

We aim here to present two models of spiral zone plate-based diffractive elements. To this end, it is shown that by a given combination of two spiral zone plates (SZPs) with opposite-signed charge strengths some novel elements are born whose phase structures are azimuthally shifted. Therefore, they are named azimuthal phase-shifted zone plates. Generally speaking, it is illustrated that both of the two models have the same diffractive functions in generating a variety of petal-like and optical ring lattice beams. Regarding the topological charge of the superimposed SZPs denoted by P1 and P2, it is also elaborated that when the modulus of |P1|−|P2| is of unity, the former beam is generated, while the values greater than unity cause the latter one to be generated. Additionally, the number of petals or lattices is simply manageable and given by |P1|+|P2|. Furthermore, defocusing surveys manifest preserving the shape of the beams in a rather long focal depth and partial rotation of them around the propagation axis is also evident. Numerical results are verified by experiments.