Study On Spectral Characteristics Of Laser-induced Shale Plasma And Design Of Quantitative Analysis Software

Laser-induced breakdown spectrometry（LIBS）is a rising and developing plasma spectroscopic analysis technology,and its physical mechanism and application have become the current research hotspots in the field of spectroscopy.In recent years,LIBS technology has shown great development potential in many fields due to its unique advantages of direct detection and analysis of solid samples.Shale resource is a kind of clean energy with abundant reserves and great potential for exploration and development.LIBS technology has also been initially applied in the shale field.In this dissertation,based on LIBS analysis technology,the elemental composition of shale was quickly obtained,the spectral characteristics of nanosecond laser-induced shale plasma were studied,the experimental method of improving spectral signal quality based on environmental gas was proposed,the element ratio method based on CF-LIBS was proposed,and the quantitative analysis software system of LIBS element ratio was designed.The research contents and main innovations of this dissertation include the following aspects:Firstly,the influence of gas environment（air,argon and helium）on plasma radiation and LIBS analysis performance of shale was studied.The time evolution characteristics of characteristic peak intensity,signal-to-noise ratio（SNR）and relative standard deviation（RSD）of geochemical identification elements（Sr and Ba）,plasma electron number density（9）₀))and plasma temperature(₀（8）).were analyzed.Experimental results show that helium gas has more stability,better curve smoothness and less error,which improves spectral resolution and signal stability.In argon,the signal intensity is enhanced,but the signal-to-noise ratio of the signal is different with the increase of signal fluctuation.It is found that the characteristic spectral lines of atoms and ions of the same element are different.In the same ambient gas,the characteristic spectra of atoms or ions of different elements have similar behavior.In different gases,the time window with high SNR and low volatility can be selected according to the evolution law,which can improve the sensitivity of analysis.In air,argon and helium,the time window is 0.5μs～2.0μs,0.5μs～3.0μs,0 to～1.0μs,respectively.In addition,the effects of complex coupled gas effects on nanosecond laser ablation of shale from the aspects of molecular mass,ionization potential and thermal conductivity are discussed in detail,combining with the mechanism of plasma morphology fluctuation and measurement uncertainty.Secondly,a quantitative analysis method for the ratio of strontium to barium based on CF-LIBS was designed for geochemical marker elements.The regression coefficients（R^2）are 0.9938,0.9977,0.9943,0.9962 at four different integration times of 1.5μs,5μs,10μs and 100μs respectively.The root mean square prediction errors（RMSEP）were 0.0424,0.0084,0.0154 and 0.0241,respectively.In this method,the basic framework of CF-LIBS method is innovatively applied.This method does not need to count all characteristic peaks of elements to calculate parameters F.Only one or two characteristic spectral lines of each element in the target element pair are selected.By optimizing the combination of characteristic spectral lines of target elements,this work further improves the quantitative analysis performance of LIBS.It performs well in practical applications and can promote the scope of application.Thirdly,we developed a LIBS element ratio quantitative analysis software system.Using the element ratio method of CF-LIBS,the quantitative analysis function is realized by programming.The software can effectively simplify the work process,improve the efficiency of analysis,and improve the accuracy and stability of analysis results,which can meet the actual needs of industrial scenes in the future.