Scientists from Xi’an Jiaotong University in Xi’an, China measured the effects of ablation craters on geomaterials occurring as a side effect of laser-induced breakdown spectroscopy (LIBS). Their work was published in Spectrochimica Acta Part B: Atomic Spectroscopy (1).
LIBS signal stability is vital when making measurements on geomaterials. However, using LIBS can be complicated by spectral fluctuations caused by variable ablation craters. To investigate the influence of ablation craters caused by LIBS laser shot accumulation, the scientists analyzed the shot-to-shot variation of plasma. Specifically, they measured aspects of shock wave propagation, ablation crater morphology, plasma morphology, and spectral evolution. All these analyses were conducted based on a fiber-optical LIBS (FO-LIBS) system.
An offshoot of LIBS, FO-LIBS has grown in popularity as well, being used in extreme environments like underwater areas and nuclear power plants. According to the scientists, using FO-LIBS “provides an optional and reliable solution for special detection situations that require separating the analysts and equipment from the probe site” (1). For this experiment, a plasma diagnostic system based on a FO-LIBS setup was established with the goal of investigating the characteristics of plasma evolution and optical emission spectra after continuous laser shots. Under various conditions, the propagation of the laser shock was compared and analyzed using the laser shadowgraph method. Afterwards, a pressure sensor monitored the shock wave waveform evolution, helping to establish the relationship between the shock wave signals and ablation crater morphology. Plasma images were created to visualize plasma morphology, and the final step of the experiment involved using optical emission spectroscopy (OES) to study the influence of the ablation craters.
What the scientists first noticed was that in most cases, spectral intensity first increases rapidly and gradually decreases. They attributed this to the conflict between the enhancement of spatial confinement and the plasma cooling phase. Additionally, they noticed strong self-reversal due to laser pulse accumulation, increasing plasma expanding distance. These factors strengthened the scientists’ belief in their system, with their abstract concluding, “This study illustrates the interaction of laser pulses, ablation, and plasma from different aspects, and provides a simple method to track the ablation process” (1).
(1) Shi, M.; Wu, J.; Wu, D.; Guo, X.; Qiu, Y.; Zhou, Y.; Li, J.; Sun, H.; Li, X.; Qiu, A. The Effect of Ablation Crater on Geomaterials Caused by Laser Shot Accumulation on the Laser-Induced Plasma and Shock Wave. Spectrochim. Acta Part B At. Spectrosc. 2023, 209, 106797. DOI: https://doi.org/10.1016/j.sab.2023.106797