Research On Beam Shaping Method With High Energy Utilization Based On Spatial Light Modulator

Flat-topped beams are widely used in laser processing.The traditional shaping methods have low energy utilization rate.In order to improve the energy utilization of flat-topped beams,this paper uses hybrid holograms.The flat-topped beams generated by spatial light modulator have high energy utilization and good flatness.In this paper,a beam shaping method with high energy efficiency based on spatial light modulator is presented.The main contents are as follows:Firstly,based on the basic theory of Gaussian beam and flat-topped beam,the design principle of beam shaping is introduced,the phase modulation principle of spatial light modulator is described in detail,and hybrid holograms are used to modulate the beams.The hybrid holograms are constructed according to the theory of beam shaping design,and the functions of each component of the hybrid hologram are explained.At the same time,the evaluation criteria of energy utilization and beam flatness are given for flat-topped beam.Secondly,the background grating of the Hybrid Hologram is used to remove the excess beam energy outside the mask,based on the diffraction characteristics of the step grating,the effects of the number of steps of sine,binary and blazed gratings on the diffraction efficiency and the diffraction angle are analyzed in detail,the type of the background grating and the number of steps are defined,and the step value is defined based on the theoretical formula and experimental test.At the same time,the internal grating of mask is designed,and an orthogonal grating with graded gray level is proposed.The diffraction pattern and diffraction characteristics of the orthogonal grating are described in detail,the influence of Fourier spectrum of different grating angle and mask angle on the beam quality is analyzed based on the phase Hologram,the optimum scheme of high energy efficiency and good beam flatness is determined,and the curves of diffraction efficiency and diffraction angle with grating period and the ratio of 0-order light energy to 1-order light energy to gray level are measured,the influence of grating period and gray level on the beam is also indicated.Finally,experimental analysis was carried out to analyze the influence of blazed grating step number,orthogonal grating period and gray level on beam quality.It was clearly indicated that the blazed grating step number in hybrid hologram was 3,the period of gradient gray level orthogonal grating was 125?m,and the curve of gray function is Gaussian distribution.Compared with hybrid holograms with different mask diameters,the energy utilization rate and beam flatness are obtained.When the mask diameter is 6mm,the energy utilization rate is up to 78.70%,while keeping flatness with 19.69%.The polished stainless steel surface was processed by the hybrid holograms with different mask shapes,and the polygonal pattern with good beam profile was obtained.