Research On Characteristics Of Spatial Confinement Millisecond Laser-Induced Plasma

Laser induced breakdown spectroscopy(LIBS)is a detection technology that collects and analyzes plasma spectroscopy information generated by a laser acting on a target material to achieve rapid information acquisition.In this paper,the work of space confinement combined with millisecond laser is analyzed and discussed.Finally,the intensity of plasma spectrum is increased and the stability is improved.It shows that space confinement can greatly improve the detection accuracy and experimental repeatability of ms-LIBS,to meet the rapid detection of elements.The millisecond laser-induced aluminum plasma has spectral enhancement at different confinement plate spacing.The results show that the confinement effect is the best when the plate confinement plate spacing is 4.5mm,the ablation pit is the deepest,and the maximum enhancement factor is 4.94 times.After fixing the confinement plate spacing of4.5mm,8 different energies are selected and the enhancement factor of each characteristic spectral line was calculated.The changes of the ablation pit morphology of different laser energies with or without constraints are discussed,the electron temperature and electron density of plasma with different energies are calculated with or without space confinements.Finally,it is shown that as the energy gradually increases,the surface area of the ablation pit gradually increases,and the electron temperature and density of the plasma increase.On this basis,the self-absorption effect of millisecond laser-induced aluminum plasma is studied.The optical thinness criterion and the self-absorption coefficient SA are introduced,and the change of the self-absorption coefficient with the laser energy with or without constraints is calculated.According to the obtained self-absorption coefficient,the intensity of the characteristic spectral line is re-calibrated.The result shows that the self-absorption coefficient SA gradually decreases due to the continuous increase of laser energy,and the degree of self-absorption increases;the corrected intensity value and theoretical intensity Value coincides,and the self-absorption coefficient The method can achieve the purpose of spectrum correction.Finally,the quantitative analysis and calculation of Fe element in the plasma of the flat plate space constrained millisecond laser ablation of aluminum alloy are carried out.With or without plate space confinement,the RSD values of the calibration curves for Fe element Fe ? 345.99 nm and Fe ? 369.51 nm are 0.828%,0.902%and 3.592%,5.824%,respectively.Use external standard method,internal standard method and SVM to establish the ms-LIBS calibration model for Fe in aluminum alloy standard samples.The results show that the calibration curve of ms-LIBS to Fe element with or without plate space constraints is obtained by using SVM method The fitting correlation coefficients R~2,RMSEC,RMSEP and ARE are 0.989,0.053wt.%,0.032wt.%,3.125%and 0.967,0.105wt.%,0.044wt.%,7.268%,respectively.The combination of ms-LIBS and SVM method can greatly improve the quantitative analysis accuracy and experimental repeatability of ms-LIBS,and meet the rapid detection of aluminum alloy trace elements.Through the study of space-constrained millisecond laser-induced plasma,the physical mechanism of spectral enhancement is revealed,and analytical methods to improve spectral stability and quantitative analysis accuracy are proposed,providing theoretical and experimental support for the practical application of LIBS technology.