对激光诱导等离子体参数进行诊断有多种方法, 其中采用发射光谱法对其诊断是一种重要的方法。 文中采用Nd∶YAG固态激光器, 输出波长1 064 nm红外激光与铝合金样品相互作用, 深入研究了铝合金等离子体产生早期(<1 μs)谱线轮廓、 谱线强度、 线背比、 谱线半峰宽及位移等随时间演变规律。 研究表明, 激光与物质相互作用早期, 电子数密度非常大, 电子与离子及原子之间的相互作用非常强烈, 谱线的Stark展宽效应非常明显, 导致多重谱线重叠在一起, 随时间演变, 电子数密度及电子温度的降低, 多重谱线的半峰宽越来越窄且谱线轮廓对称性越来越好。 MgⅠ285212 6 nm谱线强度早期逐渐增强, 大约100 ns左右谱线强度达到最大值, 然后谱线强度呈逐渐减小的趋势, 这是由于等离子体产生早期, 电子及离子占主导地位, 故早期原子谱线强度较弱, 随时间演变, 电子与离子之间的复合, 原子数密度逐渐增加, 故原子谱线逐渐增强, 达到最大值之后, 由于等离子体激发温度的降低, 故谱线强度逐渐减弱。 以NIST波长位置为参考, 等离子体产生的早期谱线发生了红移, 连续背景强度随时间演变呈幂函数形式急剧递减, 与之相反, 谱线的连续背景强度与谱线强度相比, 连续背景衰减的速度更为迅速, 故导致谱线信背比随时间演变呈增大趋势, 本研究对等离子体早期这些现象从理论角度进行了深入探讨。

There are many methods to characterize plasma parameters for laser-induced plasma, optical emission spectra method is a very important one to diagnose laser-induced plasma parameters. In this paper, Nd∶YAG solid state laser which output 1 064 nm wavelength interact with aluminum alloy sample, the temporal evolution of spectral line profile, spectral line intensity, continuum intensity, line to background intensity ratio, spectral line broadening and spectral line shift were investigated in detail for laser induced aluminum alloy plasma. The results show that the interaction of electrons between atoms and ions are very intense, which leads to electrons production of laser induced plasma at the early stage. Stark broadening effect of spectra lines are distinct and multiple spectral lines are overlapped. With temporal evolution, the electron density and electron temperature decreased quickly, the multiple spectral lines are separated slowly, and the spectral line profile is becoming thinner and symmetric. For Mg Ⅰ 2852126 nm characteristic spectral line, the intensity increased with temporal evolution at first, the intensity reached maximum value about 100 ns, and then the intensity decreased with temporal evolution, which is due to the fact that electron and ion are dominated at early stage of laser-induced plasma, atomic spectral line is very weak, with temporal evolution, the process of recombination between electrons dominated and the atomic number density increased, when the atomic number density reached maximum value, the spectral line intensity decreased with temporal evolution because excitation temperature decreased quickly. Taking wavelength in NIST database as reference wavelength, the spectral line shift for MgⅠ 285212 7 nm and Zn Ⅱ 206200 4 nm take place red shift at early stage of laser induced plasma, the continuum intensity decreased dramatically by power law with temporal evolution, on the contrary, comparing with continuum intensity and spectral line intensity, continuum intensity attenuate sharply, the line to background intensity ratio increase with temporal evolution. This early phenomenon of laser induced aluminum alloy plasma were discussed in detail from theoretical perspective.