| As one of the greatest inventions of the 20th century,laser has been widely used in fields such as medical treatment,industry and laser weapons.With the rapid development of modern optics,laser technology has become more and more mature,providing new ideas,new principles and new applications for many fields.However,when Gaussian beams,the basic laser mode,are used in optical micro-manipulation,laser processing,super-resolution focusing and other fields,their control ability is gradually insufficient.Therefore,more and more researches have begun to pay attention to the flexible control of laser light to generate light fields with richer structures.The polarization state distribution of the vector beam varies with space and is non-uniform.By adjusting vector beams with different polarization states and phase distributions as the incident light,it has important research value for flexibly adjusting the laser light field.At present,the light field theory that uses phase and polarization to simultaneously modulate vector beams is relatively scarce,which is not enough to meet the needs of optical micromanipulation,laser processing,super-resolution focusing and other fields.Therefore,this paper proposes the method of mixing polarization and phase modulation,based on the Richards-Wolf vector diffraction theory,to realize the flexible control of the vector beam focusing light field,so as to make up for the lack of control ability of the single modulation method.Design a special phase structure and combine it with polarization modulation to explore in detail the focusing characteristics and potential applications of Bessel-Gaussian beams and hyperbolic cosine-Gaussian beams on the focal plane after being focused by a high numerical aperture lens.The main research content of this paper is as follows:1.A spatially varying quadratic phase is designed to modulate a Bessel-Gaussian vortex beam.The analytical formula of the light field intensity distribution of the beam is deduced based on the vector diffraction theory.Based on the analytical formula,the effects of the beam parameter γ and the number of topological charges l on changing the optical field distribution and the optical gradient force distribution are discussed in detail by using Matlab simulation calculation.It is found that when γ is less than 3.2,the focus moves to the central area after merging.When γ exceeds 3.2,the focal spot starts to separate along the X axis.Therefore,the focal spot intensity can be concentrated,and the focal spot length can be controlled by changing the beam parameters.Furthermore,optical trapping and regular intensity peak separation features are observed as the number of topological charges l increases.The increase of the beam parameters will make the gradient force rings move toward the central region and gather together;the adjustment of the number of topological charges will generate a square gradient force array distributed in the central region.2.A polarization-mixed eccentric phase modulated hyperbolic cosine-Gaussian vortex beam is designed.Based on the theory of vector diffraction,the analytical expression of the light field intensity distribution of the beam is deduced when the beam is tightly focused on the focal plane.Based on the analytical formula,the effects of eccentricity parameter K,polarization parameter P,phase tuning parameter n and beam parameter β on beam focusing characteristics are discussed in detail by Matlab simulation calculation.It is found that by adjusting the eccentricity parameter K,the initial point-like focal spot can be transformed into a focal ring.In order to explore the principle of focal spot change more deeply,we will discuss in detail the three component fields of radial,axial and angular.It can be found that the longitudinal field increases the length of the chain,the transverse field increases the width of the chain,and the angular The field doesn’t have much impact.By adjusting the beam parameter β,the double-stranded structure can be changed into a single-stranded structure,but the length of the chain is not affected.By adjusting the polarization parameter P,the two focal spots in the focal area can be dispersed laterally,the original single focal spot can be split into multiple focal spots,and evolved into a chain structure.Finally,by adjusting the phase tuning parameter n,the purpose of adjusting the variation of the light spot is also achieved.3.A hybrid modulation method of polarization,delta phase and Airy phase is designed to modulate hyperbolic cosine-Gaussian vortex beams.Based on the theory of vector diffraction,the analytical expression of the light field intensity distribution of the beam is deduced when the beam is tightly focused on the focal plane.Based on the analytical formula,the effects of topological charge number m,polarization parameter P,triangular modulation parameter n,beam parameter β and numerical aperture NA on the tight focusing characteristics of the beam are discussed in detail by Matlab simulation calculation.It is found that by adjusting the polarization parameter P,the splitting of the adjustable focal spot on the optical axis can be realized,and further increasing the polarization parameter P will make the focal spot form a chain structure.When the parameter n of the triangular phase modulation is adjusted,the focal spot produces a series of changes.Increase the triangular modulation parameter n,and the initial two focal spots evolve into a light chain.As the parameter n continues to increase,the light chain evolves into parallel light spots along the optical axis plus a light chain,and then evolves into two parallel lights.Chains,along with the patterns of the light chains also undergo dramatic changes.By adjusting the beam parameter β,the original "butterfly" pattern evolves into a light needle structure.In order to understand the cause of the evolution characteristics of the light spot at a deeper level,the light field intensity was quantitatively analyzed,and the influence of the beam parameter β on the proportion of the longitudinal component and the transverse component in the total field was explored.In addition,by adjusting the number of topological charges m,a controllable focus shift phenomenon is produced. |
