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 the 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 a 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 the relative standard deviation (RSD) reduced with increasing interpulse delay up to 3 µs; at this delay, the minimum RSD of ∼3.86% with an intensity enhancement factor (IEF) of ∼8.70 relative to that at 0 µs was achieved for the Cu I 515.32 nm line. The emission intensity and RSD values were improved by ∼3.24 times and ∼24.30 times, respectively, relative to those obtained by single-pulse LIBS. The crater volume and ablation depth were approximately double that of single-pulse LIBS, while the image analysis showed a rebound and crash process of the plasma generated by the second pulse under the conditions created by the first plasma. Higher plasma ablation and plasma heating yielded higher spectral intensity, while increased homogeneity in the plasma resulted in improved signal repeatability for the DP-LIBS. Thus, selection of an appropriate interpulse delay, which depends on the energy combination of both lasers, plays a key role in improving the signal intensity and repeatability. These results will expedite the use of DP-LIBS as an effective signal and repeatability enhancement technique for various applications.