Spatially Resolved Laser-Induced Plasma Spectroscopy Under Different Sample Temperatures
LI Chang-ming1, CHEN An-min2*, GAO Xun3*, JIN Ming-xing2
1. Engineering Technology R&D Center, Changchun Guanghua University, Changchun 130033, China
2. Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
3. School of Physics, Changchun University of Science and Technology, Changchun 130022, China
Abstract：Laser-induced breakdown spectroscopy (LIBS) has become a good material identification technique. A hot research direction of laser-induced breakdown spectroscopy (LIBS) is to increase its accuracy and detection sensitivity. In improving LIBS detection sensitivity, the most important thing is how to increase the spectral intensity of laser-ablated plasma (LAP), such as spark discharge-assisted LIBS, magnetic field enhanced LIBS, spatial confinement LIBS, flame-enhanced LIBS, resonance-enhanced LIBS, double-pulse LIBS. In addition, increasing the target temperature is an effective and straightforward technique to enhance the LIBS spectral intensity and detection sensitivity. Mainly because the target temperature is rose, its reflectivity will decrease, which can enhance the coupling of the laser-target. Moreover, the target with an increased temperature will couple more pulse energy, improving the plasma intensity. Additionally, heating the material also heats the gas on its surface, resulting in a decrease in gas density. The decrease in the gas density can reduce the collision between the LAP and the gas, and the pressure decreases during the LAP expansion, which indirectly increases the spectral intensity of the LAP. The preheated target can significantly improve the spectral emission from the previously published reports, but these reports only provided spatially integrated spectra without spatially resolved spectral analysis. For this reason, it is necessary to investigate the influence of increasing the target temperature on the spatially resolved optical emission. In this paper, the copper target was heated to a higher temperature, and a Q-switched Nd∶YAG laser was used to ablate copper to generate laser-induced plasmas. By measuring the plasma emission, it was found that the preheated copper’s emission intensity was higher than that at room temperature. For spatially resolved plasma emission, the emission intensity first increased and then decreased with increasing the distance from the copper target. Furthermore, the distribution of the copper plasma was influenced by the target temperature; the spatially resolved emission region for the preheated target moved to a longer distance from the target surface than the unheated target. The study also investigated electron temperature distribution and density with the distance from the copper target. The spatially resolved electron temperature and density had a distribution similar to the emission intensity. The plasma with high temperature and high density expands further with the increase of target temperature.
Key words：Laser-induced breakdown spectroscopy; Preheated target; Plasma emission; Electron temperature; Electron density
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