Dynamics Of Laser Ablation Of Geological Standard Samples And Quantification Of Element Concentrations

laser induced breakdown spectroscopy(LIBS)technology is a kind of atomic emission spectroscopy and can be used to quickly measure the content or composition of various elements in the sample.It exhibits several unique advantages such as a high adaptability(gas,solid,liquid)without the need for special sample treatments,preservation of physicochemical sample properties,a lower sample demand,and remote control and has been widely used in various fields.A laser pulse with 532 nm wavelength,10 ns pulse duration,100?m beam spot diameter,and 30 mJ single pulse energy is used for ablating the United States Geological Survey(USGS)series of geological standard samples.By selecting the spectral data of 5 elements(Na,Ca,Fe,Al and Mg),the difference between the matrix effects of those geological samples were analyzed,and found the matrix effects of GSD-1G and GSE-1G are more different than others.And the influence of the matrix effects on Na and Ca is less than other three elements(Fe,Al,Mg).These differences in the matrix effects can lead to some errors in the measurement results.Then concentrations of Fe and Ti in different geological samples are obtained using artificial neural networks,the experiment results reveal that the relative errors of Fe in BCR-1G,BHVO-2G,BIR-1G,GSD-1G,and GSE-1G between the measured concentrations and the certified concentrations are 1.86%,5.73%,0.27%,3.86%,and 2.63%,while Ti are 1.92%,3%,2.78%and 2.47%,respectively(removed GSE-1G),which indicate that the LIBS method using back propagation artificial neural networks can reduce the effect of matrix effect and effectively determine the iron concentrations of USGS geological standard samples.In addition,the laser ablation process was accurately recorded by time-resolved pump-probe photography,and three shock waves caused by air and sample breakdown were captured.By measuring the radius of the shock wave at different times,the characteristic curve of the shock wave is simulated,and the velocity,pressure,stability and compressed air density of the shock wave are simulated.Finally,the ablation craters were analyzed by ultra depth field microscope and the ablation threshold of those samples were calculated by the radius of craters,measurement results show the ablation threshold of BCR-1G,BHVO-2G,BIR-1G,GSD-1G,and GSE-1G are 6.882J/cm~2,7.013J/cm~2,6.921J/cm~2,7.293J/cm~2 and 3.501J/cm~2,respectively.The measurement results can provide references for the selection of laser parameters.Laser denudation inductively coupled plasma mass spectrometry(LA-ICP-MS)is one of the most effective methods for the micro area in situ analysis.It has the advantages of high sensitivity,low detection limit,and can measure many elements at the same time.It is the most commonly used element analysis method in the field of earth analysis.However,the elemental fractionation effect is always a problem that restricts the accuracy of these technology.In this paper,the femtosecond LA-ICP-MS system was used to ablate the USGS series GSE-1G and stainless steel sample GBW01395 respectively,and their element signal intensity data under different laser energy were obtained.The morphology of the ablation craters of GSE-1G under different laser energy was recorded by scanning electron microscope.The fractionation factors of 4 elements(P,Si,Mn and Cr)were obtained by using Fe as internal standard and compared with nanosecond laser ablation,it is found that the femtosecond laser can reduce the fractionation effect.In addition,it is found that the difference of laser energy will also cause the fractionation effect in the process of laser ablation.Because of this phenomenon,when the concentration of the 4elements in GSE-1G is calculated by the external standard combined internal standard method(GBW01395 as the external standard matrix),the concentration of P is more accurate and the relative error is+6.76%under high laser energy.Because the Si element is still not completely ablated at 4.15 J/cm~2 laser energy,resulting in a relative error of-8.56%at this time,but still larger than the result of low laser energy.On the other hand,the results of Mn and Cr accurate enough at arbitrary laser energy and the relative error are less than 12%.Finally,when the laser energy for the ablation of GBW01395 is fixed to 3.07 J/cm~2,the element concentration of GSE-1G under different laser energy is calculated.When the slopes of signal intensity ratios for GSE-1G and GBW01395 were similar,the relative errors of the Mn and Cr concentrations were reduced to+3.46%and+4.24%,respectively,indicated that the accuracy of concentration determination could be improved by changing ablation rate.