Distribution Characteristics Of Light Field By Superposition Of Multiple Laguerre-gauss Beams

The vortex beam is a special light field with unique phase structure and novel topological characteristics.It contains a continuous helical phase factor related to the azimuth angle in the wavefront phase.The intensity at the singularity is zero and the distribution of dark spots is observed.The resulting composite light field contains different values of the topological charge and a variety of phase distributions when multiple vortex beams carrying orbital angular momentun(OAM)are superimposed.It can transmit multiple signals to improve communication capacity,and has confidentiality.It not only has extensive research on microscopic particle trapping and manipulation,optical wrenches,optical tweezers and so on,but also has attractive prospects in communication coding and transmission processing.Therefore,it is of great theoretical and application value to study the shape and evolution law of superposition of vortex beams.Based on this background,in this thesis,the distribution characteristics of light field by superposition of multiple vortex beams are mainly studied.The main works of this thesis are as follows:1.The basic theory of vortex beams.The phase gradient,orbital angular momentum and single photon energy in optical vortices are derived theoretically.Several common methods for generating special helical vortex beams are introduced.The phase,intensity and spiral spectrum distribution of Laguerre-Gaussian(LG)vortex beams are analyzed.2.Theoretical and simulation analysis of the superposition of multiple vortex beams under coaxial conditions.The angular solutions of the outer singularities and the determinants of the inner and outer fan blades of the phase for coaxial superposition of two and three Laguerre-Gauss beams are derived.The phase and intensity distribution laws are summarized when multiple vortex beams are coaxially superimposed and then transmitted a certain distance.3.Theoretical and simulation analysis of the superposition of multiple vortex beams under off-axis conditions.The superposition of two vortex beams with different off-axis parameters is studied.The results of the phase,intensity,and interference of the superposition of three different types of vortex beams are compared,and the influence of off-axis parameters on the spot is obtained.The results show that the superposition of multiple vortex beams will generate a complex spot structure.The phase and intensity distribution have regularity,which can detect the topological charge under the condition of coaxiality.The spot structure formed by the superposition of multiple vortex beams will move laterally with the off-axis parameters,and the larger the off-axis parameter,the faster the lateral movement speed,but the net topology charge will not change under off-axis conditions.This thesis is not only important for studying complex vortex structures and vortex beam detection in the future,but also has potential application value in microscopic particle capture and manipulation.