Study On The Scattering And Transmission Characteristics Of Bessel Gaussian Beam In Scattering Media

With the development of laser technology,shaped beam has attracted more and more attention as a new source,which is expected to be applied in many research fields such as target imaging,remote sensing detection and precision guidance.Atmospheric environment is one of the most common media in nature,in which a large number of small particles are distributed.When the beam propagates in the atmospheric environment between the transceiver devices,it is bound to be affected by these tiny particles.Therefore,the study on the transmission performance of shaped beam in typical meteorological environment has become an important research topic in the field of optical communication.Bessel Gaussian beam,as an approximate diffraction-free beam,has the characteristics of focusing and approximately non-diffraction.In this dissertation,the scattering and transmission characteristics of Bessel Gaussian beam in typical atmospheric environment are deeply studied.And the research conclusions have certain theoretical guiding significance for exploring the detection application of Bessel Gaussian beam in atmospheric remote sensing.In this dissertation,based on the Maxwell equations,the beam shape coefficients of high order Bessel Gaussian beam in spherical coordinate system are derived under the framework of generalized Lorenz Mie theory(GLMT),and the scattering models of high order Bessel Gaussian beam by a uniform dielectric sphere,a non-uniform core-shell sphere and a uniformly charged sphere are established.The scattering and extinction effects of single particle on high order Bessel Gaussian beam are analyzed.On this basis,combined with the particle scale distribution in different scattering media,the transmission performance of high order Bessel Gaussian beam in typical meteorological environments is studied.The main research contents and achievements include the following aspects:1.A scattering model of spherical scatterer to high order Bessel Gaussian beam is established.The key point of studying the interaction between the arbitrary shaped beam and the spherical scatterer is to solve the beam shape coefficients(BSCs)of the incident beam in the spherical coordinate system.Therefore,based on the GLMT and the plane wave angular spectrum expansion method,the beam shape coefficients of high order Bessel Gaussian beam with different polarization states are derived for the first time,and then the expressions of beam expanded with vector spherical wave functions are obtained.The energy distribution of beam on particles is an important factor leading to the scattering and extinction effects.Based on the homogeneous and isotropic dielectric sphere,the spatial distribution of intensity of Bessel Gaussian beams with different characteristic parameters is simulated.From the perspective of the energy distribution of beam,the influence of the characteristic parameters of beam and scatterer on the results of scattering cross section and efficiency factors is discussed.2.The transmission characteristics of high order Bessel Gaussian beam propagating in hazy atmosphere are studied.The particles in haze medium will adsorb the water vapor and form wet particles in composite forms,so two empirical models,the equivalent dielectric sphere and the heterogeneous core-shell sphere,are often used to simulate the wet particles.The equivalent dielectric sphere and the core-shell sphere have their own pros and cons in simulating wet haze particles,which can reasonably simulate aerosol particles that are difficult and extremely easy to deliquesce,respectively.Considering the different deliquescence of the three main components in the haze atmosphere,a humidity correction model is proposed in this dissertation,which can comprehensively express the hygroscopicity or deliquescence of particles in the haze medium.Ignoring the multiple scattering effects between particles,the transmission attenuation of Bessel Gaussian beam in the haze medium can be approximately considered as the superposition of the single extinction effects of all particles.Therefore,based on the scattering model of single haze particle,combined with the scale spectrum distribution obeyed by haze particles in ocean,land and stratosphere,the attenuation and transmittance of Bessel Gaussian vortex beam in the haze medium in different areas are analyzed.3.The transmission characteristics of high order Bessel Gaussian beam propagating in dusty medium are discussed.There are frequent collisions and frictions between particles in dust medium,which result in partial charges on the surface of dust particles,so the uniformly charged sphere is often used to simulate the dust particle.Under the framework of GLMT,the scattering and extinction effects of Bessel Gaussian beam by a charged sphere are simulated,and the results are compared with those of a non-uniform sphere.The particles in different dust media obey different size probability density functions.Ignoring the multiple scattering effects between particles,based on the scattering characteristics of high order Bessel Gaussian beam by a single dust particle,the transmission performance of Bessel Gaussian vortex beam in typical dust media such as floating dust,blowing sand and sandstorm is simulated.4.The effect of particle scattering on the orbital angular momentum(OAM)spectrum of Bessel Gaussian vortex beam is investigated.Whether the scattering effect of scatterer will cause the dispersion of orbital angular momentum modes of Bessel Gaussian vortex beam is very important for studying the inversion of beam parameters and environmental parameters when Bessel Gaussian vortex beam propagates.According to the spiral spectrum expansion method,the calculation of weights of OAM modes requires sampling the spatial intensity and phase of the beam.There are two common sampling methods,sampling along the circumference and sampling the whole detection area.The consistency of the conclusions of these two sampling methods,as well as their pros and cons are discussed in this dissertation.In addition,by analyzing the correspondence between the characteristic parameters of the irradiated particles and the OAM spectrum of Bessel Gaussian vortex beam,it can be confirmed that the spiral spectrum of scattered field carries some information of the spherical scatterer.