Research On Improvement Methods Of LIBS Measurement Accuracy And Applications

Laser-induced breakdown spectroscopy(LIBS)is an atomic emission spectroscopy technique used to detect the elements composition of samples in any physical state.The technology has the advantages of in-situ online detection need not more complex pretreatment of samples,simultaneous analysis of many different elements online,strong ability to adapt to harsh environments,as well as remote detection and analysis can be performed.However,compared to the traditional elemental analysis methods,due to the limitation of analysis precision,the development and promotion of this technology in practical applications have been severely hindered.Therefore,the researches on methods and applications for improving the precision of LIBS measurement is of great significance for the further development of this technology in the practical application of element detection.In order to improve the precision of LIBS measurement,the researches are mainly carried out from the three following aspects of sample powder doping,screening of chemometric methods and laser beam shaping:(1)Improvement of LIBS measurement precision based on powder doping method:Using pure graphite powder,copper powder,potassium bromide powder,and polyethylene powder to mix with several rock powders with different substrates.By optimizing the amount of powder doping and comparing the results of quantitative analysis of Ca and Mg elements in the rocks,the stability of plasma temperature and electron density before and after powder doping,the influence on matrix effect and the improvement of LIBS measurement precision are investigated by the powder doping method.The results show that the doping of graphite powder and rock powder can not only reduce the influence of matrix effect,but also improve the accuracy of LIBS measurement.(2)Improvement of LIBS measurement precision based on chemometric analysis methods:The 8 elements of Ca,Si,Fe,Al,Mg,Na,K,and Ti in three groups of raw cement samples were quantitatively analyzed by three traditional methods of standard curve,partial least-squares regression analysis method(PLSR)and support vector regression analysis method(SVR)respectively,the measure concentration range and the ability of improve the matrix effect and predict precision of the three models is studied.The results show that compared with the other two analysis methods,the nonlinear support vector regression analysis method has a larger concentration detection range,which can effectively reduce the influence of matrix effects and improve the accuracy of LIBS measurement.(3)Improvement of LIBS measurement precision based on the laser beam shaping method:The shaping of the laser beam are realized by using diffractive optical elements and flat convex cylindrical lenses changed the profile and energy distribution of the laser beam;The effects of laser beam shaping on spectral characteristics,plasma temperature and electron density,and measurement precision are studied by comparing the quantitative analysis results of Mn and Cr elements in steel samples,and Fe,Al,Mg and Na elements in cement clinker and the stability of plasma temperature and electron density.The results show that both laser beam shaping methods can effectively improve the precision of LIBS measurement.The main innovations of this thesis are:(1)By mixing different types of powder samples in rock powder samples of different substrates,the improvement of the matrix effect and precision of LIBS in measuring rock samples are studied.(2)Quantitative analysis of the content of each element in three groups of cement raw material samples using chemometric methods.The support vector regression analysis method is proposed,which can effectively reduce matrix effects,increase the detection concentration range,and improve the precision of LIBS measurements;(3)Two types of laser beam shaping methods that using diffractive optical elements and flat convex cylindrical lenses to change the laser beam profile and energy distribution are proposed to improve the precision of LIBS measurement and the elements in the steel sample and cement clinker sample were quantitatively analyzed.The related explanations are made from the comparison of ablation crater morphology,spectral stability,measurement precision and plasma characteristics.