Investigation of the secondary breakdown of double-pulse laser-induced breakdown spectroscopy with different focusing geometries and positions

Abstract

The influences of the focusing geometry and axial focusing position of the second laser pulse on orthogonal double-pulse laser-induced breakdown spectroscopy (DP-LIBS) were investigated. In this work, the petroleum coke samples were investigated by DP-LIBS in the atmosphere. The plasma morphology, emission intensity enhancement, signal repeatability, plasma temporal evolution, and plasma properties were systematically studied under different conditions. The results reveal that the focusing geometry and axial focusing position play an important role in the emission intensity and repeatability of the DP-LIBS signal. With spherical aberration minimized focusing geometry, the emission intensity and repeatability of the DP-LIBS signal were improved. In addition, the spectral intensity and repeatability also depend strongly on the axial focusing position of the second laser pulse. The images of plasma by the fast imaging technique show that the secondary breakdown almost occurs on the boundary of the first laser formed plasma. The confinement effect and emission enhancement can be observed when the secondary breakdown occurs on both sides of the first plasma boundary. The present results in this work show that there exists an optimal focusing geometry and axial focusing position that could realize emission enhancement as well as better signal repeatability in DP-LIBS, which shows great potential for the application of DP-LIBS detection.