Propagation Dynamics And Autofocusing Characteristics Of Circular Array Airy Vortex Beams

Since Airy beams were first proposed in 1979,they have attracted great attention due to their three unique optical characteristics of self-reconstruction,self-bending and non-diffraction.Airy beams have wide application such as super-resolution imaging,particle manipulation,optical bullets and biological medicine.Vortex beams have spiral phase wave front,and the center of vortex manifest as a dark core,where the intensity is zero.Because vortex beams carry orbital angular momentum,they can be used in optical communication,particle rotation,information coding or other fields.Due to the unique optical characteristics of Airy beams and vortex beams,this paper combines them organically and proposes circular array Airy vortex beams(CAAVBs).In laser medical treatment,the traditional optical tweezers technology focuses the Gaussian beams highly and have the advantages of non-contact and no mechanical damage.Gaussian beams will cause thermal damage to normal cells during focusing,so it is necessary to keep low intensity before reaching diseased cells.However,the auto-focusing beams formed by the CAAVBs maintain a relatively low intensity before focusing,and its intensity increases rapidly after reaching the focusing position.Based on this property,the beams are of great significance in laser medical treatment and other fields.The main research work are as follows:Firstly,the theories of Airy beams and vortex beams are introduced,respectively,and their optical properties are studied.Then,two-dimensional Airy beams are circularly distributed and arranged to form a circular array Airy beams(CAABs).Since each Airy beam constituting the CAABs have a self-bending characteristic,Airy beams gradually accelerate during propagation to form a self-focusing beam.At the same time,by changing the position of the two-dimensional Airy beams and the angle between the two wings of Airy beams,various CAABs can be obtained.Then,optical vortices are introduced into CAABs to obtain CAAVBs.The propagation characteristics of three kinds of CAAVBs are demonstrated.The on-axis,off-axis single vortex and vortex arrays are imposed in the CAABs,respectively.When the optical vortex is located in the center of the CAABs,the position of the optical vortex doesn’t not change during propagation,and when reaching the focusing position,the CAAVBs becomes a hollow core surrounded by a high-power ring;When an off-axis single vortex is introduced,the optical vortex will move during propagation,and finally the optical vortex locates near the center of the beams.When vortex arrays are imposed,it is divided into two situations: if the topological charges of the optical vortex are identical,the optical vortices do not fuse at the focusing position,thus forming a hollow core;If the topological charges numbers of optical vortices are opposite to each other,they will eventually fuse during propagation,thus forming a solid focus with high power and tightly focus at the focusing position.Meanwhile,the auto-focusing performance of the beams are studied in case of different array numbers,different topological charge and opposite topological charges.As the array number increases,the intensity of the beams increases,but the auto-focusing ability of the beams cannot be improved.Different topological charges have different effects on the focusing performance of the beams.Under the same parameters,when the topological charges are opposite to each other,the auto-focusing performance of the CAAVBs can be greatly improved.Finally,in order to flexibly control the auto-focusing,the positions of the CAAVBs are discussed in case of the array radius,the transverse scale factor and the wavelength,respectively.The larger the radius of the CAAVBs,and the larger the transverse scale factor,the longer its focal length is.The longer the wavelength of the beams,the shorter its focal length is.