The Research On Scattering Characteristics Of Vortex Beams In Atmospheric Aerosol Channels

Atmospheric aerosol,as the main component of the atmospheric environment,has a very important impact on many fields such as free space optical communication and remote sensing technology.By studying the scattering characteristics of atmospheric aerosol particles,the measurement and monitoring of the atmospheric environment has gradually become a research hotspot for scholars.Vortex beams carrying Orbital Angular Momentum(OAM)have huge potential for applications in free space optical communication and lidar remote sensing due to their hollow annular light intensity distribution and spiral phase wave front.In order to explore the application prospects of vortex beams in the study of atmospheric environment,it is necessary to study the interaction mechanism of atmospheric aerosol particles and vortex beams and the transmission characteristics of vortex beams in atmospheric aerosol environments.This paper conducts theoretical and simulation research on the interaction between spherical and non-spherical aerosol particles and vortex beams,the radiating force of the beam on the particles,and the transmission characteristics of vortex beams through the atmospheric scattering channels.The specific research work is as follows:First,for the study of the scattering characteristics of a single spherical aerosol particle under a coaxial incident OAM vortex beam,a typical vortex beam,the Laguerre-Gaussian beam,is introduced.The generalized Mie scattering theory is used to analyze the relationship between the incident field and the scattering fields,the scattering phase function is used to reflect the scattering intensity of the vortex beam,the integral local approximation method is used to calculate the beam factor under the vortex beam,and the optical tweezer theory is derived to solve the scattered radiation force of the beam on the particles.Numerical simulation analyzes the influence of different particle size,topological charge number(OAM state),beam waist radius,refractive index on the relationship between scattering intensity and scattering angle,and the influence of different particle size,topological charge number(OAM state),beam waist radius,and the dielectric constants of particles and surrounding media on the relationship between the axial radiation force and the scattering distance.The results are as follows:The larger the particle size,the higher the overall scattering intensity and the more intense the distributed oscillation,the axial radiation force increases first and then decreases;The larger the topological charge number,the higher the overall scattering intensity and the greater the impact on forward and backward scattering,and when the topological charge number is 2,the negative radiation force is the largest and the particles are most easily captured;The increasing of the beam waist radius increases the scattering intensity first and then decreases but does not affect the degree of oscillation of the scattering intensity distribution,and the radiation force distribution range will expand and it has no obvious effect on the peak radiation force and particle capturing;The imaginary part of the refractive index has a greater impact on the scattering effect;The increasing in the dielectric constant of the particle causes the axial radiation force peak and particle capturing ability to decrease first and then increase,while the increasing of the surrounding dielectric constant of the particle will make the axial radiation force peak and the particle trapping ability increase monotonously.Then,for the study of the scattering characteristics of a single non-spherical aerosol particle under the coaxial incident OAM vortex beam,the internal scattering field is expanded according to the spherical-like harmonic vector wave function.The boundary condition method is used to further solve the T matrix.In the numerical simulation,the surface of three typical particles(ellipsoid particles,finite-length cylindrical particles,Chebyshev particles)must be integrated and substituted,and finally the scattering intensity is reflected by the radar cross section.Numerical simulation analyzes the influence of the particle shape,beam wavelength,particle rotation angle,ratio of semi-minor axis length of ellipsoidal particles,diameter-length ratio of finite-length cylindrical particles,and ripple parameters and deformation parameters of Chebyshev particles on the relationship between scattering intensity and scattering angle.The results show that the scattering intensity distribution curves of the three kinds of non-spherical particles show a change rule of first decreasing and then increasing with the scattering angle.,and the degree of curve oscillation is higher than that of spherical particles;the relationship between the scattering intensity of different wavelengths of the beam can be inferred as:UV light>Visible light>Infrared light;The increase in the rotation angle of the particles affects the area of positive contact between the particles and the beam,which affects the scattering distribution curve;The closer the ratio of semi-minor axis length of the elliptical particles to 1,the more intense the scattering intensity distribution oscillation;The flatter the shaped particles,the stronger the oscillation of the scattering intensity distribution,but the effect is opposite at the lateral scattering;When the ripple parameter of the Chebyshev particles is small,the deformation parameter has a greater influence on the scattering intensity distribution curve,and as the ripple parameter increases,the influence of deformation parameters on the scattering intensity distribution curve gradually weakened.Finally,for the study of the transmission characteristics of the OAM vortex beam in the atmospheric scattering channel,the atmospheric scattering channel is mainly simulated by the atmospheric scattering medium,and the electric field Monte Carlo(EMC)method is proposed for the study of transmission characteristics of the planar laser beam and the Laguerre Gaussian beam(LG)in atmospheric scattering media.Numerical simulation analyzes the effects of particle size and relative refractive index in the scattering medium on the attenuation of light intensity as the thickness of the scattering medium increases,and compares the effects of planar laser beam and LG beam with different OAM states on the attenuation of light intensity and loss of polarization caused by the increasing of the thickness of the scattering medium.The results show that the increasing in the thickness of the scattering medium leads to the attenuation of the light field intensity on the detection surface;The increasing in the particle size(meeting the Mie scattering condition)and the relative refractive index in the medium both cause the attenuation of the light field intensity to increase rapidly;Compared with a planar laser beam,the LG beam makes the light field intensity decay more slowly,and slows the depolarization process of the beam;Compared with the lower OAM state,the LG beam in the higher OAM state makes the attenuation of the light field slower,and slows the depolarization process of the beam,so that the DOP can retain a longer distance.