Spatio-temporal evaluation of Zr plasma parameters in a single-beam-splitting double-pulse laser-induced plasma

The plasma shielding effect is one of the major weaknesses of laser-induced breakdown spectroscopy (LIBS) as it causes non-linearity in signal strength. Although LIBS is typically carried out in constant laser energy, this non-linearity causes a reduction in sensitivity. In this work, we systematically examine laser-induced plasma, formed by two different excitation source modes, i.e. single pulse (SP)-excitation and single-beam-splitting double-pulse (SBS-DP)-excitation over Zr-2.5% Nb alloy. The two most important plasma parameters influencing the emission line intensity, plasma temperature (T_e) and electron density (N_e) were studied and compared for both modes of laser excitation. Comparison of the results conclusively demonstrates that due to the splitting of the laser energy in the SBS-DP mode, the plasma shielding effect is significantly reduced. The reduced plasma shielding translates to an increased laser–sample coupling under SBS-DP mode. Temporal imaging of the total intensity of the laser-induced plasma in both excitation modes was also studied. The study shows how the plasma shielding effect can be reduced to improve the analytical quality of the LIBS methodology.