Numerical Calculation And Experimental Study Of The Spatial Distribution Of Laser Light Intensity Based On Scalar Diffraction Theory

In recent years,the rapid development of laser technology has created an opportunity to"light manufacturing",which makes the development of high beam quality laser increasingly become the research focus.At the same time,the research on laser beam quality measurement technology is now a hot topic in the field,and it is gradually developing towards more accurate and faster measurement.Obtaining the intensity distribution of the laser beam in the process of spatial transmission is the main problem of the technique.The method of numerically calculating the spatial three-dimensional light field by using the two-dimensional complex amplitude of the laser can quickly acquire the light intensity distribution,which has several advantages like free of scanning and real-time,and supposed to be an effective way to be realized.However,there are still some problems in the calculation of diffraction,such as the low precision and the inability to obtain the intensity distribution with high accuracy.This thesis starts with the principle of measurement,and focuses on the mechanism of affecting the measurement accuracy based on the scalar diffraction theory.First of all,the research background and significance of this topic are described,the domestic and overseas research status of real-time measurement of spatial distribution of light intensity and numerical calculation of light field transmission is introduced.Secondly,based on the scalar diffraction theory,this thesis analyzes the expression of diffraction integral under different approximation conditions and the basic approach of algorithm realization,and analyzes the basic conditions that the numerical calculation needs to meet under certain accuracy requirements.In addition,the frequency response difference and the ability of resist undersampling of different algorithms are compared according to the simulation results.The undersampling problems in the angular spectrum transmission process are analyzed in depth and the conditions that light field sampling needs to meet after giving specific parameters are given.Thirdly,the spatial frequency characteristics of single-mode laser and multimode laser are analyzed from the view of complex amplitude distribution.In addition,several typical techniques for obtaining complex amplitudes of laser are described,and the process of solving the phase distribution of light field based on the light intensity transmission equation is studied,and the accuracy of calculating the phase distribution is verified by the simulation experiment,which provides a reliable basis for the complex amplitude transmission.Based on the process of fitting the beam transmission curve and calculating the M~2 factor,a verification model of the accuracy of the intensity distribution is established.For the calculation of beam width in the extraction of light intensity profile,the iterative method of anti noise is studied.The validity of beam width calculation and numerical transmission calculation is verified by the experimental data collection and the simulation of multimode laser transmission process.Finally,a laser complex amplitude measurement device and a scanning beam quality measurement device are set up by the method of splitting the optical path.The former measurement result is used for numerical transmission calculation to obtain the spatial light intensity distribution of the laser beam,and the beam quality factor is extracted;the latter measurement result is used as a reference for comparison.The experimental results show that the difference between the two is less than 2.5%,which proves the feasibility of calculating the spatial intensity distribution of laser light based on scalar diffraction theory.In addition,the system of collecting light intensity images at different axial positions at the same time is also built.By using this system,the complex amplitude of light field can be reconstructed,and the purpose of real-time acquisition of the laser spatial distribution and beam quality is realized.Then the stability and repeatability of the test results are analyzed.