Simulation On Laser Crater Morphology And Element Detection By Single-shot Laser-induced Breakdown Spectroscopy Of Lead

With the fast development of laser technology, especially the short-pulse laser technology, Single-shot Laser Induced Breakdown Spectroscopy (single-shot LIBS) has become one of the most important branches of material detection. This article mainly focuses on two parts: simulation of the crater morphology of Lead after laser ablation using molecular dynamics methods; analysis of the emission spectroscopy of Lead by qualitative and quantitative methods.In theoretical and simulation aspect, a new model on laser ablation is built. With the combination of unsteady-state heat conduction and embedded-atom method (EAM), a code on two dimension simulation of laser crater morphology is made and the relationship between time and crater morphology is discussed. Specifically, in simulation process, the heat transfer equation is first used to acquire the initial velocity of Lead particles; and then, the EAM, along with its forces, are applied to form the picturs of the motions and the interaction forces among particles after laser ablation and metallic bond destructions. With the study of crater morphology and the velocities of jetted-out particles, a statistical method is used to study the velocity distribution of jetted-out particles in order to find out those particles, who contribute to the 405.8 nm emission line of Lead. A ratio of the particles related to 405.8nm emission line of Lead to the total jetted-out particles is made and its variation with time is discussed.In experimental aspect, both qualitative and quantitative analysis are made to detect the content of Lead in different material using single-shot LIBS with Q-switched Nd:YAG lasers whose pulse width is 10ns. The advantages and disadvantages of single-shot LIBS are discussed and the repeatability and data process for single-shot LIBS are analyzed. Besides, the reason why 405.8 nm emission line is chosen to be the standard of Lead recognition is given. In qualitative analysis, the spectroscopes from pure Lead, glass, Pb Sn alloy and welding wire are acquired and discussed, which would highly verified the truthfulness of 405.8 nm emission line of Lead. In quantitative analysis, detections of the emission lines of pure Lead with different wavelengths: 107mJ, 139.2mJ, 171.5mJ and different pulse energies: 1064nm, 532nm, 1064/532nm are made. Spectroscopes under three conditions: 1. same wavelengths and different pulse energies for single pulse lasers; 2. same pulse energy and different wavelength for single pulse lasers and 3. same wavelengths and different pulse energies for double pulse lasers are acquired and compared.