激光诱导Ca等离子体温度的实验研究

Experimental investigation on plasma temperature of Ca by laser-induced breakdown spectroscopy

等离子体温度是激光诱导击穿光谱测量中一个重要的因素。采用Nd：YAG脉冲激光器作为光源击穿样品形成等离子体，其发射光谱由中阶梯光栅光谱仪和ICCD进行分光和光电转换。通过实验得出了300～450nm波段的光谱图，定性分析出了CaⅡ315．9，317．9，393．4，396．9nm和CaⅠ422．7nm等发射谱线。根据激光诱导击穿光谱定量公式，等离子体温度的变化对谱线强度有影响。先假设实验中等离子体处于局部热平衡状态．选用ca的4条一价离子谱线，根据Bohzmann斜线法计算出了等离子体温度，并得到了等离子体温度与Ca质量分数的关系。随着Ca质量分数的增加，等离子体温度也相应增加。但当Ca质量分数小于0．50％时等离子体温度增加的幅度较小，而质量分数大于0．50％时等离子体温度的上升幅度相对较大。最岳经过验证，实验中等离子体处于局部热平衡状态的假设成立。

The plasma temperature is an important factor in quantitative analysis by laser-induced breakdown spectroscopy （LIBS）. The plasmas were generated by a Nd：YAG laser on the surface of sample and detected by an Echelle spectrograph and an Intensified Charge-Coupled Device（ICCD）. The spectrum of 300 nm to 450 nm recorded several spectral lines of Ca component such as Ca Ⅱ 315.9 nm, Ca Ⅱ 317.9 nm, Ca Ⅱ 393.4 nm, CaⅡ 396.9 nm, Ca Ⅰ 422.7 nm and so on. It is known that the change of plasma temperature has influence on the line intensity from the equation for quantitative lABS analysis. It was assumed that the plasmas produced in the experiment were in local thermodynamic equilibrium（LTE）. The temperature variations were de duced by the four one ionized Ca spectral lines and the Boltzmann plot, and the relationship between the plasma temperature and the concentration was obtained too. The plasma temperature increased when the concentration increased. When the mass fraction of Ca was lower than 0. 50%, the increase velocity of the plasma temperature was small. When the mass fraction of Ca was higher than 0.50%, the increase was large. The hypothesis of local thermal equilibrium conditions of the plasma was confirmed in this experiment.