Time-Resolved Evaluation of Self-Absorption in Laser Induced Plasma from Nickel Sample

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 (3d(9)(D-2)4p-3d(9) (D-2)4s) of Ni were chosen for self-absorption investigation. Self-absorption of Ni 351.034 nm corresponding to the highest energy level D-3(1) of 3d(9)(D-2)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.