Reseach On A New Method For Generating Vortex Beams

A vortex beam is a beam with phase singularities and helical wave fronts.The waves cancel at the optical axis,so that the vortex beam forms a dark hollow structure.The vortex beam carries topological charge and orbital angular momentum.The unique properties of the vortex beam make it a potential application in the fields of optical manipulation,spatial optical communication,optical imaging,quantum information,biomedicine and so on.Therefore,it is of great significance to explore the methods of generating vortex beams.The contents of this thesis are include three parts as follows: one is to propose a new method of generating vortex beams;the second one is to propose a new method of generating high-order Bessel beams;and then the thesis is to propose a new method of studying the combinations of vortex beams.The main contents are as follows:A new method of generating vortex beams is proposed in the first part of this thesis.By improving the existing methods of generating high-order vortex beam with asymmetrical pinhole plates under plane wave illumination,a new multi-spiral porous screen is designed.By using the method of controlling variables,this thesis studies the following situations by software simulation: different number of spiral lines,the number of spiral lines which is different from the topology charge that is expected,different pinhole number,different pinhole radius and different distance from the first hole to the center of the porous screen.The conclusions are as follows: Only the number of spiral lines of the multi-spiral porous screen reach the same as the topology charge that is expected can the vortex beam be generated;the topological charge of the high-order vortex beam generated by this method should not be too high;by satisfying all the conditions as the number of pinholes to reach a certain quantity,the pinhole radius in the middle range and the distance from the first hole to the center of the porous screen is in the middle range,the generating vortex beam can be up to relative standard.A new method of generating high-order Bessel beams is proposed in the second part of this thesis.The parameters of the asymmetrical pinhole plates are adjusted to make the spiral of the pinhole close to the ring.Through software simulation and experimental verification,when the ring opening is small,a better high-order Bessel beam is generated.A new method of studying the combinations of vortex beams is proposed in the last part of this thesis.On the basis of the asymmetrical pinhole plates,a single helical spiral lines with opposite rotation direction is superimposed to form a new spiral porous screen which is then used to study the combinations of the vortex beam.Base on the multi-spiral porous screen presented in this thesis,a new spiral porous screen is similarly designed.The software simulation agrees well with the theoretical simulation as: bright spots appear in intensity pattern,the number of spots is twice the number of topological charge.The method proposed in this thesis has high conversion efficiency,and the experimental optical path is simple.It provides a new idea for the generation of vortex beams,high-order Bessel beams and the combinations of vortex beams.