Keywords: 
• 激光等离子体 /
• 磁空混合约束 /
• 光谱增强 /
• 冲击波压缩

Abstract: In order to explore and understand the spectroscopic characteristics of laser induced plasma and spectral intensity distribution under magnetic-spatially combined confinement, in this paper, the laser induced breakdown plasma spectral characteristics of Cu with magnetic-spatially combined confinement, obtained by the optical emission spectroscopy and the optical shadow graph are studied. The temporal evolutions of spectral intensity and the axial and transversal distributions of Cu I 521.8 nm plasma spectrum with magnetic-spatially combined confinement are analyzed. The experimental results show that the laser induced Cu plasma spectra are all enhanced under the conditions of magnetic-spatially combined confinement and spatial confinement. In addition, the maximum enhancement factors of Cu I 521.8 nm in these two kinds of confinement conditions are 2 and 1.2, respectively. The enhanced effect of plasma ion spectrum in the magnetic-spatial field is stronger than that of spatial confinement. Under the effect of magnetic-spatially combined confinement, spectral enhancement mechanisms are derived from the magnetic field and spatial mixed actions. At the early stage of plasma expansion, the magnetic field action is a dominant factor. The charged particles in plasma are affected by the Lorenz force in the magnetic field which induces the charged particles to do the Lamor cyclotron motion, then the plasma expansion is restrained and the plasma volume decreases. The frequency of collisions between the electron and ion in the plasma increases. Therefore, the spectral intensities of atoms and ions are strengthened. For the case of the larger delay time, the spectral enhancement is caused by the spatial confinement. The axial and transversal spatial intensity distributions of Cu I 521.8 nm are analyzed by the optical shadow graph method. The plasma is compressed by the shock wave because the shock wave generated by the Cu plasma is reflected by the space plate. The transversal expansion of plasma plume is constrained by the spatial confinement, which causes the spatial position of the plasma internal atoms with high densityto move forward, and also induces the maximum axial spatial location of Cu I 521.8 nm spectral intensity to be far from the Cu metal surface. The results indicate that the axial distribution of plasma plume, obtained from the optical shadow graph is corresponding to the axial distribution of plasma spectrum obtained by the optical emission spectroscopy. In summary, the spectrum enhancement of laser induced plasma with the magnetic-spatial combined confinement is influenced by two forces: one is the magnetic force and the other is the compressive force caused by the shock wave. The study of the laser induced breakdown plasma spectral characteristics of Cu with magnetic-spatially combined confinement provides a simple and powerful tool for improving the sensitivity of laser induced breakdown spectroscopy.