The effect of ablation crater on geomaterials caused by laser shot accumulation on the laser-induced plasma and shock wave

Abstract

The stability of laser-induced breakdown spectroscopy (LIBS) signal is vital for its application in geomaterials, which is challenged by spectral fluctuations caused by variable ablation craters. To investigate the influence of the ablation crater caused by laser shot accumulation, the shot-to-shot variation of plasma was analyzed from the aspects of shock wave propagation, ablation crater morphology, plasma morphology, and spectral evolution, which was conducted based on a fiber-optic LIBS (FO-LIBS) system. A pressure sensor was applied to monitor the shock wave signal due to the shock wave propagation characteristics related to the number of shots and types of binding materials. The evolution of the ablation crater profile and depth was tracked, and a linear correlation model between crater depth and shock wave energy was established. It was found that the spectral intensity increases first rapidly and gradually decreases, which can be attributed to the competition between the enhancement of spatial confinement and the plasma cooling phase. Strong self-reversal was observed due to the laser pulse accumulation, with an increase in the plasma expanding distance. This study illustrates the interaction of laser pulses, ablation, and plasma from different aspects, and provides a simple method to track the ablation process.