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Compared with the traditional spectral analysis methods, such as inductively coupled plasma mass spectrometry method, atomic absorption spectrometry method, the analysis sensitivity, accuracy and spectral resolution of the laser induced breakdown spectroscopy technology is relatively lower. Due to the advantages o f low ablation thresholds, high-spatial resolution, minimal invasion, high-efficiency transportation of femtosecond laser, the femtosecond laser induced breakdown spectroscopy method (fs-LIBS) has become an active topic in recent years. In order to further improve the analysis performance of fs-LIBS, the spatial confinement method is proposed. In this paper, the cavity confinement enhancing effect of fs-LIBS is discussed. Based on the local thermal equilibrium condition (LTE) assumption, the plasma temperature and electron density is obtained. The results shown that the plasma emission intensity, plasma temperature and electron density are improved under the given cavity constraints. In effect, the plasma generated shock wave encounters cavity barriers during its expansion, the shock wave is reflected back to the plasma center. One hand is improved the plasma temperature and electron density, on the other hand is increased the number of particles in the upper energy level, which leads to an increase in the intensity of the plasma emission spectrum. In general, the spatial confinement method combined with the fs-LIBS showed its great potential in improving the figures-of-merit of ultrafast optical LIBS technology.
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