激光诱导土壤等离子体光谱辐射实验参数优化

采用激光诱导击穿光谱法（LIBS）对土壤进行了研究。激光器采用的是Nd:YAG脉冲激光器，激光器的输出波长是1 064 nm，脉宽是5.82 ns，激光聚焦在土壤表面产生激光诱导等离子体，通过优化实验参数（ICCD延时、脉冲能量、ICCD门宽、脉冲频率、谱图积累次数）对Ca Ⅱ 393.37 nm和Ca Ⅱ 396.37 nm两条特征谱线强度及信背比的影响，确定实验最佳条件是ICCD延时1 s，激光能量50 mJ，ICCD门宽3.5 s，脉冲频率1 Hz，谱图积累次数100次。在最优实验条件下计算等离子体参数，得出土壤中的等离子体电子温度是11 604 K，土壤的等离子体电子密度是5.1551016 cm-3，经过计算，土壤样品满足LTE条件。这说明，以上关于土壤样品的等离子体参数计算结果是真实有效的。

Optimization of experimental parameters of laser induced soil plasma spectral radiation

Laser induced breakdown spectroscopy (LIBS) was employed to investigate the soil. LIBS analyses were performed with Nd:YAG laser operating at 1 064 nm, 5.82 ns pulse duration. The spectral lines of Ca Ⅱ 393.37 nm and Ca Ⅱ 396.85 nm were selected as the analytical lines for optimizing the experimental parameters (ICCD delay, laser energy, ICCD gate width, repetition rate and cumulative number of spectrum) which had influence on spectral line. The experimental conditions were determined as follows. The ICCD delay was 1 s, the laser energy was 50 mJ, the ICCD gate width was 3.5 s, the repetition rate was 1 Hz and the cumulative number of spectrum was 100 times. Under the optimal experimental conditions, the results of the electron temperatures Te and electron densities Ne were 11 604 K and 5.1551016 cm-3, respectively. The local thermal equilibrium condition of the plasma was satisfied. The results are useful for the analysis and detection of elements in soil.