Research On Flattening Of Gaussian Beam In 2μm Band Based On Diffractive Optical Element

The application prospects of 2μm-band thulium-doped fiber lasers cover industrial processing,infrared guidance,laser medical treatment,national defense and military equipment,and optical communications,especially the development of 2μm-band thulium laser scalpels,with higher beam quality The requirements make it necessary to study the flat top technology for Gaussian beam.In this paper,based on the Diffractive Optical Element(DOE),the Gaussian beam flattening technology that can be used in 2μm band thulium-doped fiber lasers is studied.Through research and analysis of the theoretical basis for the design of diffractive optical elements at this stage and the basic optimization design algorithm based on scalar diffraction theory,this paper decides to adopt the improved AFSA algorithm to design diffractive optical elements.Finally,based on the optical simulation software ZEMAX,a DOE element surface shape that can be used for Gaussian beam flat-topping is designed,and the optical system experimental verification is carried out through processing and molding combined with error analysis.The main work completed in this article is as follows:1.The research introduces the characteristics and advantages of 2μm band thulium-doped fiber laser,typical Gaussian beam flattening technology and related knowledge of diffractive optical elements.Then study the design of the diffractive optical element surface shape that can be used for Gaussian beam flattening based on the scalar diffraction theory,and analyze the existing optimization design algorithms of various diffractive optical elements based on the scalar diffraction theory,and introduce the advantages and disadvantages of these algorithms as well as limitations.2.A diffractive optical element designed for 2μm band Gaussian beam flat-topping is designed with an improved artificial fish-swarm algorithm based on the physical energy conversion model.The Gaussian beam flat-topping result is 2.1% mean square error value and 93.6% diffraction efficiency.The optimization design results of Gerchberg-Saxton algorithm and Simulated Annealing are compared.Simulation analysis by MATLAB software shows that the improved AFSA algorithm is significantly better than the other two,which proves that the improved AFSA algorithm can be more effective in designing diffractive optical elements that can be used for 2μm band Gaussian beam flattening.3.The optical simulation software ZEMAX was used to design the diffractive optical element,and the ZPL macro command was written to realize the automatic optimization of the software.The diffractive optical element that can be used to flatten the Gaussian beam of the 2μm-band thulium-doped fiber laser was successfully designed,and the actual surface of the element was obtained.Phase distribution.Furthermore,in this paper,the diffractive optical element is processed into shape and combined with error analysis for experimental performance verification.