Investigation On The Interaction Between Complex Particles And Vector Vortex Beams

Optical vortex is a special light field with spiral wavefront and orbital angular momentum.This property has important potential applications in many fields such as optical micro-operation,optical microscopy,and optical communication.In this dissertation,the definition and description of the vector vortex beam are mathematically clarified,the electromagnetic field of the vortex beam is accurately described,and the expression of the electromagnetic field component of the vortex beam under different polarization states is derived.The characteristics and dynamic characteristics such as energy density,momentum density,spin angular momentum and orbital angular momentum of the vortex beam is theoretically analyzed.For the basic theory of the interaction between the vortex beam and complex particle,we specifically analyze the Rayleigh scattering model of spheroid and electromagnetic scattering model.The theoretical calculation method of the light force and optical moment applied to the particles by the light field is described.The method of moments(MOM)and the fast multipole method(FMM)for solving the integral equations are used to study the interaction between the vortex beam and the different complex particles in the electromagnetic scattering model.The main work and results are as follows:1.Firstly,the electromagnetic field of the vortex beam should be accurately described.The definition and description of the vortex beam are mathematically defined.Based on the definition of the vortex beam and its scalar solution,the vector is rationally constructed by the relationship between the electromagnetic field and the vector potential and the scalar potential.Potential,the electromagnetic field component expressions of two typical vortex beams of Laguerre-Gaussian beam and high-order Bessel beam are derived.Energy,momentum and angular momentum(spin and orbit AM)are the main dynamical characteristics of light and matter.These quantities are crucial for understanding the physical properties of light and matter,as well as the interaction mechanism between the both.From the classical Maxwell electromagnetic theory,the orbital angular momentum characteristics of the optical vortex are analyzed,and it is proved that the optical vortex orbital angular momentum is indeed determined.The polarization characteristics of the vortex beam and the dynamic characteristics such as energy density,momentum density,spin angular momentum and orbital angular momentum are theoretically analyzed in detail.2.In-depth study of the theoretical methods for solving the interaction between complex particles and vortex beams,especially the non-spherical Rayleigh model and the electromagnetic scattering model based on the surface integral equation.A program for analyzing spheroids as the simplest non-spherical Rayleigh particle interacting with vortex beams was written.The effects of vortex beams on the mechanical effects of non-spherical Rayleigh particles in different three-dimensional orientations of spheroids and different polarization states are analyzed.For the interaction of complex shape particles with vortex beams,the method of moment method based on surface integral equation and fast multipole method are used to study the scattering problem of vortex beam.It is also indicated that the results could provide a theoretical basis for the next step to study the interaction mechanism between vortex beam and complex shape particles.3.We investigates the interaction between al vortex beam and a homogeneous dielectric particle with arbitrary shapes using a full-wave numerical method based on the surface integral equation.The method of moment based on PMCHW equation and its fast algorithm program are written.For a numerical solution,the particle with arbitrary shape is modeled by using surface triangular patches and the surface integral equation is discretized with the method of moments.The resultant matrix equation is solved by using an iterative solver in combination with the multilevel fast multipole algorithm to obtain the equivalent electric and magnetic currents introduced on the surface of the particle.The above methods are used to study the scattering of high-order Bessel vortex beams and Laguerre Gauss beams from complex shaped uniform medium particles,such as cones,cubes,spindle-shaped particles,disk-like particles similar to red blood cells,and hourglass type.Particles and icosahedral particles were analyzed in detail for the effects of some beam parameters on their differential scattering cross sections.At the same time,numerical results concerning scattered field in the far zone and radiation force are presented for various parameters of the incident beam and of the particle.These numerical results can be used as a reference for studying the interaction between particles of arbitrary shape and vortex beam using other numerical methods or experimental operations.4.This study investigates the electromagnetic scattering of a vortex beam by multiple dielectric particles of arbitrary shape based on the surface integral equation(SIE)method.In Cartesian coordinates,the mathematical formulas are given for characterizing the electromagnetic field components of an arbitrarily incident vortex beam.By using the SIE,a numerical scheme is formulated to find solutions for characterizing the electromagnetic scattering by multiple homogeneous particles of arbitrary shape and a home-made FORTRAN program is written.From our simulations,the beam's order,half-cone angles,and the ways of particles' arrangement have a great influence upon the differential scattering cross section(DSCS)for multiple particles.It is anticipated that these results can be helpful to understand the scattering mechanisms of a high-order Bessel vortex beam on multiple dielectric particles of arbitrary shape.5.The scattering of a beam by typical composite particles consisting of an inclusion within a host particle is investigated.The incident beam is represented by the vector expressions in terms of electric and magnetic fields that perfectly satisfy Maxwell's equations.The scattering problems involving arbitrarily shaped composite particles with an inclusion are formulated with the surface integral equation method.As an example,the effects of the beam's and particle's parameters on the differential scattering cross section for a composite particle that consists of a spherical inclusion within a host sphere are analyzed in detail.Then the numerical results for the scattering of a high-order Bessel vortex beam by several typical nonspherical composite particles with an inclusion are presented.It is anticipated that these results can provide useful insights into the scattering of a vortex beam by composite particles.