Morphology–spectral correlations of laser-induced Al plasma with plate wall spatial confinement

Abstract

Laser-induced breakdown spectroscopy (LIBS) suffers from shot-to-shot fluctuations that constrain signal intensity and stability. While spatial confinement effectively enhances emission signals, the quantitative relationship between plasma plume morphology and spectral characteristics remains unclear, limiting mechanistic understanding and optimization strategies. This study establishes a three-tier hierarchical correlation framework connecting spectral characteristics, global plasma morphology and local morphological features using Pearson and Spearman correlation analysis. We employed optical emission spectroscopy (OES), high-speed photography, and shadowgraphy to analyze with plate wall spatial confinement (PWSC), correlations between morphological parameters (axial length, radial length, plume area, total integrated image intensity, average pixel intensity, region of interest integrated intensity and axial-to-radial ratio) and spectral characteristics (intensity, stability, enhancement factors). Results show PWSC altered morphology–spectrum correlations: at 7 μs, spectral enhancement reached 1.88 fold with RSD reduced from ∼12% to 5.8%. Notably, the AL/RL-intensity correlation reversed from strong positive (0.94 to 0.997) to moderate negative (−0.38 to −0.46), while RL intensity correlation strengthened dramatically (0.13 to 0.95), highlighting RL dominant role under confinement. These findings provide mechanistic insights into confinement-induced plume dynamics and establish a foundation for correlation-weighted plasma image-spectrum fusion optimization in high-precision elemental analysis.