An Investigation On The Laser Induced Breakdown Spectroscopy Of The Metal Element In Soil

The investigation on the laser induced micro-plasma by the radiation focused on a solid surface plays an important role in the production of super-conduct films and nanometer materials, laser isotope separations, medicine, biology, and other industrial applications. Elemental analysis based on the emission from the plasma generated by focusing a high power density laser beam on a solid sample surface is known as laser-induced breakdown spectroscopy (LIBS). LIBS has power potential to be used to detect trace elements in the sample matrix that include gases, aerosols, and liquids. The high sensitivity of the technique, the free sample preparation, the minimal destroy of the sample, and its suitability to remote measurements are generally concerned by scientific researchers. LIBS has successfully used to detect the trace elements in metal alloy and the control of the trace element concentration in stove, but there are few works reported on the application of LIBS to quantitative detection of the heavy metal elements in soil. The focus of this thesis is listed as following: The experimental measurement, analysis, and assignment of the LIBS spectra of the soil in the visible spectral region(300-450nm) are studied. The LIBS detection limit for Pb element in soil is also obtained. The application of the calibration-free method in the quantitative elements analysis is discussed finally.In chapter one, the basic concept, characteristic, some diagnostic techniques, and the application of the laser-induced plasma are introduced briefly.In the second chapter, a brief introduction of the basic theory about the laser plasma, the space structure of the laser plasma, several models to deal the laser induced plasma dynamics, the broadening of the spectral lines and two important character of the emission spectral, and the method to measure the electron temperature are presented.In chapter three, the experimental setup and method are introduced in detail with the description of the ablation laser, spectrum detection system and preparation of the soil samples.In chapter four, we investigate on the Laser-induced breakdown spectroscopy of the trace metal element Pb in Soil. The main contents are as followings: (1) The LIBS spectra of the soil are measured in the visible spectral region in our experiment. The main and some trace elements of the soil sample are obtained by the analysis and the assignment of spectral structure and spectra lines respectively. The experimental results show that the major elements in soil sample are Si, Al, Fe, Mg and so on and the trace elements are Mn, Pb, Cr. (2) Additionally, the intensities of Pb 405.78nm spectral line are measured at the different concentration of Pb in soil. The LIBS calibration curve of the analytical spectra line is obtained by internal calibration, and the value of detection limit, 36.7ppm, is obtained from the fit of the calibration curve.In the last chapter, the Calibration-Free method is applied in the quantitative major elemental analysis in soils, the main contents are as followings: (1) The elements contained in the soil sample are presented by the analysis of the measured laser-induced breakdown spectroscopy in our experiment and the plasma electron temperature,4200-4500K,is obtained from the measured spectral line intensities of the Laser-induced breakdown spectroscopy. (2) Based on the results mentioned above, we make an investigation on the concentration of the ten major elements such as Si,Fe,Al,Mg etc. in soil by calibration-free method and their content in soil are obtained as well.