Propagation Properties Of Vortex Beams With Orbital Angular Momentum In Random Atmospheric Turbulence

The transmission of laser in turbulent atmosphere plays an important role in many applications,such as free space optical communication(FSO),biomedicine,national defense and military,Lidar,optical detection and optical manipulation.When the laser propagates in the turbulence,it is affected by the turbulence,which leads to the change of the propagation characteristics of the laser and further affects the beam quality.Vortex beam has its special helical phase structure,and its orbital angular momentum can be used as an information carrier.Vortex beam has great potential to encrypt data,so vortex beam has higher application value than traditional Gaussian beam.Random atmospheric turbulence has a serious influence on the propagation of vortex beams,and random atmospheric turbulence will cause turbulence effects such as beam flicker,spread,drift and so on.Therefore,the study of the influence of random atmospheric turbulence on the propagation characteristics of vortex beams with orbital angular momentum has important reference value and reference significance for military and other fields.In this paper,with the aim of reducing the influence of random atmospheric turbulence on beam propagation,the propagation characteristics of vortex beams with Orbital Angular Momentum in non-uniform atmospheric turbulence and anisotropic non-Kolmogorov atmospheric turbulence are studied by means of numerical simulation.The main contents of this thesis are as follows:1、The purpose and significance of this paper are introduced,the research and development of vortex beams at home and abroad are analyzed,and the research progress of beam propagation in turbulent atmosphere is summarized and analyzed.In this paper,the basic theories and methods of laser transmission are briefly introduced,several common atmospheric turbulence power spectrum models and atmospheric refractive index structure constant models are introduced,and the generalized extended Huygens-Fresnel principle,Wigner distribution function and intensity moment theory are briefly introduced.2、The numerical analytical expressions of root mean square space expansion,root mean square angle expansion and M~2 factor of vortex beam with OAM in non-uniform atmospheric turbulence are derived.And through numerical simulation,the effects of different beam parameters(beam width,coherence length,beam wavelength)and different turbulence parameters(turbulence inner scale,zenith angle)on relative root mean square space expansion,relative root mean square angle expansion and relative M~2 factor are analyzed in detail.The relative M~2 factor of electromagnetic Gaussian Schell beam and vortex beam with OAM are numerically simulated and compared when they are affected by different turbulence parameters and beam parameters.3、Based on the second moment theory of Wigner distribution function and the power spectrum of anisotropic non-Kolmogorov atmospheric turbulence,the expressions of root mean square space expansion,root mean square angle expansion,M~2 factor and radius of curvature of vortex beams with OAM are obtained.The numerical simulation results show that the propagation characteristic of the beam depends on the variation of atmospheric refractive index structure constant,coherence length,generalized exponential parameter,anisotropy parameter,internal scale of turbulence and initial degree of polarization.