Research On Bessel Vortex Beam Propagation And Target Echo Characteristics In Complex Environment

Vortex beams are beams of light with orbital angular momentum(OAM)and have a wide range of potential applications,such as laser communication,imaging,and radar.However,when transmitted in complex environments,vortex beams are affected by atmospheric turbulence,suspended particles,aerosols,and rain and fog particles,which cause scattering and absorption,resulting in distortion of the beam’s intensity and phase.This,in turn,leads to beam spreading,wander,and attenuation of transmission power.These factors limit the performance and transmission range of optical systems in complex environments.Bessel vortex beams have some unique advantages that can overcome these limitations.Firstly,Bessel vortex beams have self-healing capabilities,allowing them to refocus and restore their original rotational phase structure when encountering obstacles or disturbances.This self-healing ability enables Bessel vortex beams to effectively deal with obstacles and interferences in the transmission path,maintaining the integrity and stability of the beam.Secondly,Bessel vortex beams have non-diffraction characteristics,which can resist the effects of beam phase distortion,path spreading,and defocusing caused by short-distance atmospheric turbulence.This non-diffraction characteristic gives Bessel vortex beams better transmission performance in complex atmospheric environments,effectively reducing beam transmission loss and distortion.By fully utilizing the self-healing capabilities and nondiffraction characteristics of Bessel vortex beams,the performance of optical systems in complex environments can be improved,the transmission range can be expanded,and the stability and reliability of the beam can be enhanced.This is of practical significance for applications in laser communication,imaging,radar,and other fields.This paper explores the transmission behavior of Bessel vortex beams in complex environments through numerical simulations and experimental methods.These complex environments include atmospheric turbulence,rainfall,and underwater bubble curtains.The research focuses on the intensity and phase distortion of Bessel vortex beams in these environments,as well as the turbulent effects and target scattering characteristics in double-pass channels caused by these distortions.The main research content and achievements of this paper are as follows:1.The simulation method for the transmission of laser beams through multiple layers of atmospheric turbulence using phase screens has been improved by employing a grid-based dense meshing technique.By precisely controlling the Fried parameter between adjacent phase screens,accurate and fast modeling of Bessel vortex laser beams in the transmission through multiple layers of random phase screens under weak turbulence conditions is achieved.Numerical simulations were conducted to study the intensity and phase distortion phenomena of Bessel vortex beams during their transmission through atmospheric turbulence.Using statistical averaging methods,the influence of atmospheric turbulence parameters and Bessel vortex beam source parameters on the intensity evolution,beam spreading,and wander effects caused by intensity distortion were analyzed.Additionally,the impact of phase distortion on the distribution characteristics of the OAM spectrum was investigated.By extracting the positions of phase singularities of Bessel vortex beams at every ten meters along the atmospheric turbulence transmission link,the vortex splitting effect of Bessel vortex beams and the laminar-to-turbulent evolution process during their transmission through atmospheric turbulence were analyzed for the first time.2.Building upon the atmospheric turbulence multi-layer phase screen transmission model for Bessel vortex beams,the transmission model was extended to double-pass transmission,and the echo characteristics of Bessel vortex beams after target scattering in a double-pass turbulent atmospheric channel were studied.In the double-pass atmospheric turbulence link,the echo process of Bessel vortex beams after classical target scattering,including flat mirrors,corner reflectors,and Gaussian rough surfaces,was simulated.Through mathematical and statistical methods,the effects of different scattering targets and atmospheric turbulence on the intensity,phase distribution,OAM spectrum,and optical scintillation index of the echo signals of Bessel vortex beams were discussed.The influence of the OAM topological charge and waveform parameters of Bessel vortex beams on the echo signals was analyzed in detail.By studying these echo characteristics,a deeper understanding of the stable transmission and target identification aspects of Bessel vortex beams in practical applications can be achieved.3.Within the framework of the generalized Lorenz-Mie theory,the single-scattering interaction between Bessel vortex beams and raindrop particles was studied.The scattering and absorption effects of raindrop particles on Bessel vortex beams were analyzed,and the variations of scattering,absorption,and extinction factors of Bessel vortex beams were investigated under different wave source parameters.Additionally,by incorporating a raindrop size distribution model,the energy transmission attenuation characteristics of Bessel vortex beams in rainy atmospheres were studied for the first time.The research results confirmed that compared to Gaussian beams,vortex beams have stronger penetration capabilities in scattering environments,and the energy attenuation rate decreases with an increase in the topological charge of the OAM mode.Furthermore,in the near-infrared wavelength range,Bessel vortex beams exhibit strong penetration capabilities in rainy environments,while in the mid-infrared wavelength range,Bessel vortex beams are subject to absorption by raindrop particles,resulting in significant energy attenuation and reduced transmittance.4.Under the framework of the generalized Lorenz-Mie theory,a model for the singlescattering interaction between a Bessel vortex beam and underwater bubble clusters has been established.By analyzing the scattering and absorption of Bessel vortex beams by underwater bubble clusters,the energy attenuation of Bessel vortex beams in an underwater bubble environment is discussed.High-quality Bessel vortex beams were experimentally produced,and a simulation apparatus for underwater bubble clusters was established to study the transmission attenuation characteristics of vortex beams in an underwater bubble cluster environment.Intensity distributions of different laser probing sources after passing through the simulated underwater bubble cluster apparatus were measured,and the transmission power attenuation of the underwater bubble cluster environment was calculated to explore the transmission behavior of vortex beams and Bessel vortex beams in different states of underwater bubble cluster environments(including different bubble cluster thicknesses and volumes).The impact of changes in bubble volume and bubble cluster thickness on their transmission in underwater bubble clusters is a key focus of discussion.