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Heavy Element Cr Analysis of Soil by Dual-Pulse Laser-Induced Breakdown Spectroscopy

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Tutor: GaoXun
School: Changchun University of Science and Technology
Course: Optics
Keywords: Laser induced breakdown spectroscopy,orthogonal pre-ablationmechanism study,quan
CLC: TN249
Type: Master's thesis
Year:  2014
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Abstract:
In this paper, research status of soil elements were summarized and analyzed first, then laser induced breakdown spectroscopy (LIBS) was come up to apply to the fast on-line detection of soil. The development present situation of LIBS at home and abroad and the application in the field of soil testing were detailed introduced. Orthogonal pre-ablation dual-pulse LIBS was came up to effectively reduce the detection limit of LIBS technology, and confirmed that the pre-ablation dual-pulse LIBS has the feasibility in the aspect of soil testing. Thus the work of soil element analysis was carried out by using pre-ablation dual-pulse LIBS.The experiment systems of dual-pulse LIBS in different combination of pulse were set up successfully in the experiment, including nanoseconds combined with nanosecond pulse laser, femtosecond combined with nanosecond laser pulses, femtosecond plasma silk and nanosecond laser pulse combination of double pulse LIBS experiment system. The relation between the position of two pulses in which we got the highest signal of spectral enhancement was got by optimizing the space position relations of pulses and the experimental parameters. The tendency of the double pulse enhancement ratio and time delay in different combination of pulse conditions were got by change the time delay between the two pulses. Spectral enhancement mechanism of pre-ablation dual-pulse LIBS was discussed by analysing the variation tendency of spectral enhancement and delay of two pulses in different pulse combination, and combining with plasma electron temperature, electron density and the change of plasma plume in different time delay.Six kinds of known standard soil samples were made by adding different amount Cr2O3into every10gram of GSF-1soil sample which was bought from China standard material network. In optimum conditions, we used different pulse combination ablation this6kinds of soil samples respectively and mapped the calibration curve of Cr elements in soil. By comparing the calibration curve of single with double pulse, we knew the femtosecond tight focus under the condition of double pulse LIBS has the lowest detection limit which is0.31ppm, and single pulse condition¡¯s lowest detection limit is the application of femtosecond plasma silk, which is3.65ppm. The purpose of the lower detection limit of LIBS is implemented.
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