Research On Optical Field Control In Laser Cutting

The focus position,focal spot size and spot energy distribution of laser cutting have a very important impact on the quality and efficiency of laser cutting.In this thesis,the optical field control of laser cutting optical system is researched to improve the quality and efficiency of laser cutting.The main research work is as follows:(1)A four lens group zoom laser cutting optical system is designed.The system is composed of compound collimator group,zoom lens group,compensation lens group and focus lens group.The physical model of the four lens group zoom optical system is established,and the movement law between each lens group is deduced,The size of laser focal spot can be adjusted from 1 to 3.75 times,and the focus position can be adjusted from-20 mm to + 10 mm.The size and position of laser focal spot can be adjusted accurately,and the imaging quality of the system is optimized and simulated.It can meet the cutting requirements of different materials and thickness.(2)A laser cutting optical system of annular spot based on vortex beam is designed.By combining spiral phase plates which generate vortex beams with different topological charge,the zero intensity region of annular spot center can be adjusted.Under the same laser source and focusing conditions,the spot diameter of a vortex beam with topological charge is 1.9 times that of a Gaussian spot,the peak energy is reduced to about 1/4,and the Rayleigh length is expanded to 1.7 times.Theoretical analysis shows that the vortex beam can transfer the excessive central energy of the original fundamental mode Gaussian beam to the edge of the slit,and improve the Rayleigh length(depth of focus)of the system,which can improve the quality of edge cutting.The vortex beam with larger topological charge can enlarge the zero intensity region in the center,which can be used more flexibly in laser cutting.(3)On the basis of the existing laser cutting head,an annular spot cutting head is made by adding a spiral phase plate to generate a vortex beam with topological charge of 1.The experimental study is carried out by using a 1000 W fiber laser.Under the same cutting speed of 200 mm / s and the same defocusing amount of zero,the width of the front and back slit of the stainless steel cutting plate with thickness of 0.5 mm is wider than that of the original one,and the quality of the cutting section is better than that of the original cutting head.