Influence of Key parameters on Signal Quality in Double-Pulse Laser Induced Breakdown Spectroscopy (DP-LIBS)

Abstract

The instability of spectral signals is a major challenge in double-pulse laser-induced breakdown spectroscopy (DP-LIBS) and a primary factor of instability is the inhomogeneity of the laser-induced plasma. First, we studied the influence of energy combination of the two laser pulses on signal intensity, repeatability and the interpulse delay, and then systematically investigated the impact of a key parameter, the interpulse delay on spectral intensity and repeatability using spectral, image, and crater analyses of brass sample. Maximum enhancement was achieved when the second pulse interacted with the plasma at an interpulse delay that allowed optimal laser absorption and increased material ablation. The emission intensity increased and relative standard deviation (RSD) reduced with increasing interpulse delay upto 3 µs where the minimum RSD of ~ 3.86% with the intensity enhancement factor (IEF) of ~ 8.70 relative to those at 0 𝜇s was achieved for Cu I 515.32 nm line. These values were ~ 3.24 times and ~ 24.30 times improved relative to those by single pulse LIBS, respectively. The crater volume and ablation depth were approximately double to that with single pulse LIBS while the image analysis showed a rebound and crash process of the plasma generated by the second pulse in the conditions created by the first plasma. Higher plasma ablation and plasma heating yielded higher spectral intensity while a more homogeneity in the plasma resulted in improved signal repeatability in DP-LIBS. Thus, selection of an appropriate interpulse delay, which depends on the energy combination of both lasers, plays a key role for the signal and repeatability improvement. These results will expedite the use of DP-LIBS as an effective signal and repeatability enhancement technique for various applications.