Study On The Diffraction Characteristics Of Square Spiral Zone Plates

Fresnel zone plate with small size and light weight,has been used for both visible light and non-visible optical band such as X-ray and extreme ultraviolet.Also,its unique focusing characteristics make it suitable for X-ray microscopy,photolithography and some other fields.Vortex beam,which carries orbital angular momentum,is the beam with a spiral shape structure in the wavefront.In addition,the light intensity at the singularity which is produced by the uncertainty or mutation of the beam,is zero.These properties make the vortex beam have research value in optical micromanipulation,information communication and other fields.This paper presents a systematic research on the diffraction characteristics of square spiral zone plate and explore the potential applications of the square optical vortex.The main points of the paper are as follows:1.Firstly,the development history of zone plates and related researches at home and abroad are introduced.The basic theory of vortex beam and scalar diffraction theory used in this paper are described,in which Fresnel-Kirchhoff diffraction will be used as the theoretical support for the simulation part of this paper.Next,the design principle and diffraction characteristics of the square fractal zone plate and square spiral zone plate are introduced.Mostly,the design principle and the diffraction properties of square Fresnel zone plate with spiral phase are presented.2.A methodology called dual-type fractal spiral zone plate is introduced,which has both phase-type and amplitude type.With the properties of Cantor fractal and spiral phase plate,this element can realize a sequence of tunable co-axial optical vortices.The design method of this optics is introduced and the numerical simulations of this element by MATLAB are presented.Moreover,the focusing performance follows a modulo-4 transmutation rule.3.Based on the square spiral zone plate,the single focused square spiral zone plate which can suppress high order diffraction,is produced.Both the simulations and visible experiment results verify this element with the structure of random arranging quadrilateral-shaped nanometer structure apertures along each zone,which has the ability to generate single focused square optical vortex beam.