Mechanisms of non-monotonic signal dependence on repetition rate in high-repetition-rate nanosecond LIBS

High-repetition-rate nanosecond laser-induced breakdown spectroscopy (LIBS) offers advantages such as small ablation crater and high signal-to-noise ratio. To investigate the non-monotonic influence of repetition rate on signal intensity, we conducted high-repetition-rate LIBS experiments over a range of 10–100 kHz under controlled pulse energy (∼115 μJ/pulse). Multi-dimensional diagnostics were performed, including measurements of plasma temperature and electron density, plasma morphology, temporal dynamics, gas-flow control, and ablation crater morphology. The results indicate that the increase in signal intensity at lower repetition rate is primarily attributable to the pre-heating mechanism, while the subsequent decrease at higher repetition rate is due to aerosol scattering and the formation of a surface recast layer. The competition mechanism between the signal enhancement (pre-heating) and the attenuation effects (aerosol scattering and recast layer formation) is further supported by the optimum repetition rate shifting toward lower values as the pulse energy increases. This work suggests that high-repetition-rate LIBS holds significant potential for micro-damage analysis and microscopic elemental imaging. A better understanding of the multi-pulse energy coupling mechanism provides an important reference for optimizing parameters to achieve improved LIBS signals.