激光诱导击穿光谱(LIBS)技术是一种新兴的元素分析技术, 但自吸收效应对LIBS测量的影响较大。 文中利用Nd∶YAG激光器产生的基频1 064 nm脉冲激光在空气中击穿镍靶产生等离子体, 观测了四条跃迁对应同一电子组态(3d9(2D)4p—3d9(2D)4s)谱线NiⅠ 341.476/351.034/351.505/352.454 nm的自吸收现象。 实验发现, 谱线NiⅠ 351.034 nm没有出现自吸收现象, 其下能级电子组态为3d9(2D)4s的各能级中能量最高的3D1态。 对于其他三条谱线, 在等离子体辐射初期自吸收较为严重, 随着等离子体的演化, 自吸收减弱。 不同谱线的自吸收持续时间不同, 其中谱线NiⅠ 352.454 nm自吸收最为严重, 且当门延时为1 100 ns时仍存在明显自吸收现象, 而NiⅠ 341.476/351.505 nm的自吸收持续时间分别为900和500 ns。 自吸收现象随着激光脉冲能量的增加而减弱。 结果表明通过选择合适的谱线、 激光脉冲能量和较长的探测门延时可以有效避免自吸收现象对LIBS测量的影响。 文章还对不同谱线自吸收持续时间不同的原因进行了讨论。

Laser induced breakdown spectroscopy (LIBS) has been shown to be a promising technique for element analysis. However, self-absorption effect deeply influences the LIBS measurements. In the present paper, a Q-switched Nd∶YAG laser operated at 1 064 nm was used to generate nickel plasmas in air. Four atomic lines Ni Ⅰ 341.476/351.034/351.505/352.454 nm which belong to the same electronic configuration (3d9(2D)4p—3d9(2D)4s) of Ni were chosen for self-absorption investigation. Self-absorption of Ni Ⅰ 351.034 nm corresponding to the highest energy level 3D1 of 3d9(2D)4s was not observed in the plasma emission investigated. While for the other three lines, a strong self-absorption appeared at the prophase of the plasma and tended to weaken. The self-absorption at Ni Ⅰ 352.454 nm was the most serious and still visible at the delay of 1 100 ns, compared with the lines of Ni Ⅰ 341.476/351.505 nm whose self-absorption duration is 900 and 500 ns respectively. It was also found that the self-absorption effect had power dependence and decreased with the increase in laser pulse energy. The obtained results suggest that the self-absorption effect could be alleviated by suitable atomic line selection, operating at a higher pulse energy and detecting with a longer delay. The possible reasons for the self-absorption duration difference for different lines were also discussed.