Atmospheric Propagation And Applications Of Partially Coherent Beams With Special Spatial Structure

Optical coherence is an important degree of freedom of light manipulation.Laser beams can have some unique propagation characteristics with manipulating the coherent structure of the beams,such as self-focusing,self-shifting,self-shaping,self-splitting,self-healing and so on.Because coherent structure manipulation can induce the peculiar propagation characteristics,it has important application value in the fields of free-space optical communications,particle control,particle capture,optical imaging and material processing.This thesis mainly researches the applications of coherent structure manipulation in free-space optical communications.Based on the generalized Huygens-Fresnel principle,the propagation characteristics of laser beams in free space and turbulent atmosphere are studied.Moreover,we also study how to reduce the negative effects caused by turbulent atmosphere on laser beams by coherent structure manipulation,such as propagation factor,beam wander and scintillation.Firstly,the representation of scalar(vector)partially coherent beams is introduced.The basic theory of laser beam propagation in free space and turbulent atmosphere and the models of atmospheric turbulence are introduced.The negative effects caused by turbulent atmosphere,such as propagation factor,beam wander and scintillation,are also introduced.Secondly,introducing the models of the main research object,which can be divided into two categories:one is the uniformly correlated partially coherent beams,including the Hermite-Gaussian correlated Shell-model beams,optical coherence lattices and optical coherence vortex lattices.The other one is the non-uniform correlated beams include Hermite non-uniformly correlated beams,rectangular Hermite non-uniformly correlated beams,radially polarized Hermite non-uniformly correlated beams and non-uniform Laguerre-Gaussian correlated beams.The propagation characteristics of the two kinds of partially coherent beams in free space are studied.Moreover,we study the propagation characteristics of this two types beams with special spatial structure in turbulent atmosphere,analyz the negative effects of atmospheric turbulence on the laser beam.Discussing the changing of the value of propagation factor,beam wander and scintillation of uniform correlated beams and non-uniform corrlated beams in turbulent atmosphere,respectively,and analysis the ability of anti-turbulence of these beams.In addition,this thesis also introduces the experiment setup for generating partially coherent beams with special spatial structure and the measuring setup for studing the propagation characteristics of laser beams after through the thermal turbulent.Recording the quivering beam spot and analyzing the beam wander of Hermite-Gaussian correlated Schell-model beams,scintillation of partially coherent radially polarized vortex beams and enhanced backscatter of vortex beams.And we also introduce how to simulate atmospheric turbulence and the propagation behavior of laser beams in turbulent atmosphere by random phase screen program.The scintillation of partially coherent radially polarized vortex beams and optical coherence vortex lattices in turbulence,the exhanced backscatter of vortex beams in turbulence are studied by the random phase screen program.Comparing the experiment results and simulation results,we find they are consistent,which proves the feasibility of the random phase screen program.Finally,the application of partially coherent beams with special spatial structure in image information loading and transmission is explored.The image quality of partially coherent light beams with image information passing through free space,random phase screen,milk medium and turbulent atmosphere is studied in theory and experiment.