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An Investigation on Morphology Simulation and Detection Application in Laser Induced Breakdown Spectroscopy of Lead

Author: JiangZuoZuo
Tutor: ZhangGuiZhong
School: Tianjin University
Course: Photonics technology
Keywords: Laser-induced Breakdown Spectroscopy Plasma Molecular Dynamics Simulation Laser-ablation Lead Rapid Analysis
CLC: TN241
Type: Master's thesis
Year: 2009
Downloads: 39
Quote: 1
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Abstract


At present, Laser Spectroscopy has been developed to Laser Induced Breakdown Spectroscopy (LIBS) with the rapid development of short pulse laser technology. In this paper, LIBS is discussed in both the theory of molecular dynamics algorithm and the improvement of the experimental device, which mainly includes:(1) In theoretical simulation, a 2-D molecular dynamics program based on the potential theory of embed-atom model is compiled in combination with subarea and layering theory. This program can successfully handle the molecular dynamics simulation of femto-second laser ablation of pure lead samples, and the longest simulation time reaches 1ns, which is closer to the plasma development time in experiment. Through the analysis of ablation simulation results, the characteristics of the laser ablation are achieved: the ablated material is divided into crystal area, melted zone and ablation region, in which the motion has the movement feature of particles in solid, liquid and gas respectively. What is more, we obtain the ablated plasma morphology, the ablation hole shape and the ablation depth. At the moment that samples have just been ablated for 1ns, the ablated particles length and width accord with the size of plasma in practice. Besides, the ablation hole depth and its influence on the spectrum in the experiment are analyzed.(2) In experiment, firstly, with comparison among experimental equipment we demonstrate the reasons why the conventional CCD is chosen based on both theory and experiment. Secondly, the spectral lines are analyzed and signal reproducibility of LIBS is testified by means of multiple measurements for average. Moreover, the best excitation energy of pure lead sample is found. we deeply analyze the broad band spectrum absorbed in emission spectra and explain the formation of it with the hypothesis of transient steady state, which enriches the content of it greatly. The phenomenon of the lost of Pb characteristic spectroscopy is also discussed. In application, the materials with different lead content, for instance glasses, are used as samples to evaluate the feasibility of lead-detection with the experimental equipment mentioned above from both qualitative and quantitative aspects. It is finally testified that the device in this experiment can realize rapid lead detection and the predicable detection limit is 74ppm. And the plan of decreasing the detection limit by space- resolved spectroscopy is also proposed.

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CLC: > Industrial Technology > Radio electronics, telecommunications technology > Photonics technology,laser technology > Laser technology, the maser > Laser physics and basic theory
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