Study On Scattering Characteristics Of Vortex Beams By Aerosol Particles

Atmospheric aerosols have important implications for the development of the free-space laser communications,microwave communications,and remote sensing technologies.How to improve the real-time monitoring and measurement of atmospheric aerosol by laser radar has become one of the current research hot spots.The existing laser radar systems usually use plane wave or Gaussian beams as light sources.The vortex beam is a special light field with spiral phase wavefront and hollow ring intensity distribution.It carries an Orbital Angular Momentum(OAM),which has important potential applications in free-space laser communication and laser radar remote sensing.In order to promote the application of vortex beam in the above two fields,we need to study the interaction mechanism between aerosols and vortex beam.This paper mainly focuses on the scattering of vortex beam by typical aerosol single-sphere particles,aerosol core-shell particles,and aerosol particle groups,and the influence of relatively humidity change in atmosphere on the scattering of aerosol particle.The main research work of this paper is as follows:Firstly,typical atmospheric aerosol models and the generalized Lorenz-Mie scattering theory are introduced.Based on the generalized Lorenz-Mie scattering theory,the scattering characteristics of a single aerosol particle by plane waves and Gaussian beam are studied.The effects of relative humidity on the scattering characteristics of aerosol particles are analyzed.Secondly,based on the mathematical transformation relationship between Laguerre-Gaussian(LG)mode and Hermite-Gaussian(HG)mode,the scattering of LG vortex beam by atmospheric single aerosol particles model is established.The Radar Cross Section(RCS)of a typical aerosol particle by the LG vortex beam is calculated by solving the scattering coefficient of the single sphere of the LG vortex beam.The effects of relative humidity on the RCS of the LG vortex beam are compared with that of plane wave and Gaussian beam.The results show that the LG vortex beam has better capability of detecting the changes in relative humidity than the plane wave and the Gaussian beam.In addition,with the increase of the relative humidity in the atmosphere,the atmospheric aerosol adsorbs moisture and condenses to form a core-shell structure in which the aerosol particles are covered with a layer of water.Based on the single-sphere scattering model of the LG vortex beam,the scattering effect of aerosol core-shell particles by a LG vortex beam is studied.The double station results of the core-shell particle by the LG vortex beam with normal incidence are numerically calculated.The effects of different orders of radial mode order,topological charge,particle size,and refractive index on the scattering characteristics are analyzed.The results show that there is a clear difference between the RCS of the single aerosol and the core-shell particle,which shows that the double layer structure is more practical in the case of relatively high relative humidity.Finally,based on the scattering model of LG vortex beam by aerosol single-sphere particles,the scattering properties of LG vortex beams by a typical aerosol particle group satisfying a certain spatial distribution is studied.The effects of the relative humidity on the scattering and polarization characteristics of aerosol particle group by vortex beam are discussed.