| Material element analysis is a project that is closely related to social development and people's production and life.It plays an irreplaceable role in material inspection,waste recycling,environmental protection,archeological identification,and even food safety.In recent decades,the spectral analysis technology has been used more and more in the elemental analysis.Laser induced breakdown spectroscopy?LIBS?,as a typical atomic spectroscopy analysis technology,is called"future star"of chemical analysis technology with its unique advantages,such as compact equipment,without requiring sophisticated sample preparations,and capability of remote,in-situ analysis.However,some problems,including low analytical sensitivity and spatial resolution,difficulty in simultaneously increasing analytical speed and analytical sensitivity,and requiring standard calibration for quantitative analysis,have seriously affected the performance of element analysis and application range of LIBS.To solve these problems,this paper has carried out research on the laser-induced breakdown spectroscopy combined with laser-induced fluorescence?LIBS-LIF?and high repetition rate laser-ablation spark-induced breakdown spectroscopy?HRR LA-SIBS?.According to the different principles and characteristics of the two techniques,the methods to improve the analysis sensitivity,spatial resolution,analysis speed and quantitative analysis without requiring matrix-matched standard samples were explored.The technology have been improved based on their different principles and characteristics,and the methods of improving the analytical sensitivity,spatial resolution,analysis speed,and quantitative analysis of calibration elements without standard samples have been explored,including the following four contents:1. The LIF enhancement principle of lead atom is analyzed theoretically.A tunable dye laser,which is homemade,is used to build a LIBS-LIF experimental device system with an Nd:YAG laser.The enhancement factor of this system compared with the traditional LIBS technology is studied.This LIBS-LIF system was used to detect the trace amounts of lead in water.To eliminate the influence of a water matrix to spectral analysis?e.g.,light blocking due to water splashing and plasma emission quenching due OH groups?in the plasma during direct analysis of water samples,a wood-slice substrate was selected as a water absorber to convert liquid-sample analysis to solid-sample analysis.After optimizing the parameters,such as the moving speed of the sample platform,the wavelength and pulse energy of the LIBS laser,the delay between the two laser pulses,and the pulse energy of the LIF laser,the calibration curve of lead in water samples was created and the limit of detection was found to be 0.32 ppb,two orders of magnitude better than that obtained by analyzing water samples directly using the same LIBS-LIF technique.2. Based on the highly sensitive detection and the characteristics of only one beam ablating the sample surface,LIBS-LIF was applied to the study of the surface elemental microanalysis of solid samples with submicron lateral resolution.A 532 nm or 266 nm nanosecond laser pulse with low pulse energy was used to realize submicron laser-ablation on the surface of a copper alloy,and LIF technique was used to sensitively detect a minor lead element in the ablated samples.In the experiment,a copper alloy containing 1.5%lead was used as sample.The size of the smallest scale craters ablated by the LIBS laser beam at two wavelengths on the sample surface was observed and the spatial resolution was evaluated.?344 nm and?267 nm lateral resolutions could be achieved experimentally under 532 nm and 266 nm laser ablations under the current experimental condition,respectively.This demonstrated the feasibility of using a LA-LIF technique for surface elemental microanalysis of solid samples with submicron spatial resolution.The potentials of continually improving the spatial resolution of this technique to nanoscale were discussed.3. High repetition rate laser-ablation spark-induced breakdown spectroscopy?HRR LA-SIBS?combined with lock-in signal detection was developed to realize sensitive.In order to realize the lock-in signal detection,the repetition rate of laser pulses was increased to 4 k Hz and the time duration of the plasma emission was prolonged to be about 10 microseconds by the spark discharge,thus the duty cycle has been increased to 4%approximately.An OPA 695chip was used to fabricate a gated preamplifier that can reduce the continuum background of the plasma emission.Trace lead and aluminum in brass samples and trace chromium and manganese in aluminum alloy samples were analyzed experimentally.The detection limits of them were estimated to be about 112,178,235 and 202 ppb under current experimental condition,demonstrating an obvious improvement on the analytical sensitivity of this technique comparing with conventional single pulse laser-induced breakdown spectroscopy.The HRR LA-SIBS technique combined with lock-in signal detection can be potentially applied to realize directand sensitive elemental analysis of different solid samples.4. Calibration-free?CF?method combined with high repetition rate laser-ablation spark-induced breakdown spectroscopy?HRR LA-SIBS?was first utilized to realize rapid and standard-free elemental analysis of alloy samples.A compact fiber laser operated at 30 k Hz pulse repetition rate was used to ablate the sample and the spectra were recorded with a compact fiber spectrometer in non-gated signal recording mode.Three standard aluminum alloy samples were analyzed to evaluate the performance of this technique.After obtaining the spectral data of the three aluminum alloy standards in the experiment,Median filtering method was applied to reduce the contribution of the continuum background to the intensity of the atomic lines.Then,the electron density was estimated from the Stark broadening of four appropriate ionic lines.The averaged value of electron density was determined to be?2.36-2.49??1017 cm-3.11,800.±800 K averaged plasma temperature was estimated from the Saha-Boltzmann plots.The Mc Whirter criterion and the Critoforetti additional criterion verify that the plasma is close to a local thermodynamic equilibrium state.Finally,the concentration of each element in the aluminum alloy standard is calculated according to the Saha-Boltzmann plot.Compared with the standard value,the plasma could be verified to be in a state close to local thermodynamic equilibrium.The analytical error was<0.5%for the major element and<35%for minor elements with>0.1%concentrations.It was demonstrated that CF method combined with HRR LA-SIBS was possible to realize reliable quantitative elemental analysis for aluminum alloy samples. |
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