Investigation on plasma morphology fluctuation in laser-induced breakdown spectroscopy analysis of particle flow due to stochastic particle ablation

Abstract

Plasma morphology fluctuation is the primary source for signal uncertainty of laser-induced breakdown spectroscopy (LIBS). This study has investigated the plasma morphology fluctuation due to stochastic particle ablation in LIBS particle flow analysis. K-means clustering was employed to analyze a large set of spectral data, identifying four plasma patterns: weak, moderate, air-prominent, and extreme plasma. As the excitation probabilities of four plasma patterns differed, the analytical signal statistic concerning the particle ablation deviated from the Gaussian distribution but aligned with the generalized extreme value distribution. For each plasma pattern, the pulse-to-pulse plasma morphology fluctuation in terms of plasma length and center position was investigated by time-resolved imaging. The dominant particle ablation process was evaluated through particle distribution images. Weak plasma with the most fluctuated plasma length and moderate plasma with the most fluctuated center position contributed to considerable signal uncertainty. Air-prominent and extreme plasma presented more repeatable signals due to less plasma morphology fluctuation. The pulse-to-pulse relative standard deviations of particle emission for the weak, moderate, air-prominent, and extreme plasma were 60.68%, 41.75%, 38.62%, and 22.20%, respectively. All these results suggest a plasma modulation pathway for particle flow analysis.