Discrete Dipole Approximation For Electromagnetic Scattering By Targets And GPU-accelerated Research

Based on the mechanical effect of the convergent laser beam,the optical tweezers can manipulate the micro nano particles.On the study of the mechanical effect of laser beam,it is necessary to study the interaction between the beam and the arbitrarily shaped particle.The discrete dipole approximation(DDA)can be applied to the study of electromagnetic scattering of arbitrary shape particles with arbitrary beam incidence.Based on this,DDA can be used to study the mechanical effect of laser beam on irregular particles,which is helpful to the development of optical tweezers technology,the discovery of new mechan-ical effects and the development of new optical tweezers technology.In the development process of DDA,there are some problems,such as slow computation speed and high mem-ory consumption,which hinder the popularization and application of DDA.GPU parallel computing architecture can accelerate the computing speed of DDA algorithm and enhance computation capability of DDA.In this paper,GPU is used to accelerate the DDA,and the scattering effects of the particles on the beam(plane wave,Gaussian beam and vector Bessel beam)are studied.The main research work of this paper is as follows:1.The multiplication of an arbitrary vector with a matrix is the main operation in the D-DA,which determines the computation time and memory consumption of the method.This paper combines GPU with open source software ADDA to achieve the acceler-ation of DDA,firstly,the consistency between the program based on GPU and serial program is verified,On the basis of this,we discuss the acceleration ratio of the mul-tiplication of an arbitrary vector with a matrix in ADDA with the increasing number of dipoles,The simulation results show that,when the number of dipoles reaches 1,099,136,the computation time based on CPU serial is about 75 times of GPU par-allel.2.The distribution of the incident field,the near field,the internal field and the radiation force of the spherical particles under the plane wave,the Gaussian beam and the vector Bessel beam are calculated.In the calculation of the electric field distribution,the near-field and the internal field distribution of spherical particles with different beam centers,waist radius Gaussian beam and different order,beam center and half-cone angle vector Bessel beam incidence are discussed respectively.At the same time,the inhomogeneous particles are simulated,and the electric field distribution of the shell particle with the different beam centers Gaussian beam and the different orders vector Bessel beam incidence is discussed.Radiation force calculation is divided into two kinds of situations.Plane wave and Gaussian beam incidence,The radiation force at each dipole position is discussed,and in the case of vector Bessel beam,the radiation force of the whole target is discussed.The internal field and near-field distribution of spherical particles with Gaussian beam and vector bessel beam are calculated by using the generalized Mie theory respectively.At the same time,the contribution of single scattering to the scattering process is discussed by using Debye series.The simulation results show that different Debye order can save different light and filter out the remaining light.When p = 1,in the ball after a refraction of light can be retained;p ? 2,The light that has passed through two times in the ball is not filtered.3.The Mechanical effect of different beams on different shapes of particles are calculated by DDA.In this paper,three kinds of particles(spheroid,ellipsoid and rectangular particle)are selected,and the radiation force distribution on the three kinds of particles is calculated under the irradiation of the vector Bessel beam.The numerical results show that the radiation force distribution of the particles with different shapes in the Bessel beam field is related to the shape of the particles.The radiation force acting on the spherical particles presents a concentric circle distribution,the radiation force distribution acting on the ellipsoidal particles is elliptical distribution and the radiation force acting on a cuboid is rectangular distribution.