Energy deposition rhythm for optimizing high pulse repetition frequency LIBS signals under scan speed-laser frequency interaction.

In microjoule high pulse repetition frequency laser induced breakdown spectroscopy systems, the traditional single-variable parameter optimization method can only analyze the effects of scan speed and laser frequency independently, without considering the interaction effect between these two factors. To address this issue, an optimization strategy based on energy deposition rhythm (EDR) was proposed for the proportional optimization of scan speed and laser frequency. To begin with, the interaction between scan speed and laser frequency was analyzed using two-factor analysis of variance. Based on this, the effects of proportionally increasing scan speed and laser frequency on spectral signals were investigated by maintaining a constant ratio between the two parameters under different EDR conditions, followed by quantitative analysis based on the optimized spectral signals. The results indicated that, at a fixed EDR, proportional increases in scan speed and laser frequency maintained a constant spatial interval between adjacent laser pulses, thereby reducing the interference caused by pulse-spacing variations in local ablation overlap and related ablation conditions. Meanwhile, this proportional increase also resulted in a larger number of laser pulses contributing within the fixed 20 ms integration window owing to the increase in laser frequency, thereby enhancing the accumulated spectral emission while maintaining signal stability. The accumulated spectral intensities of Mg, Mn, and Fe increased by approximately 4-9, 5-10, and 4-10 times, respectively. The most pronounced quantitative improvement was observed under EDR = 1/400, where the R2 values for Mg, Mn, and Fe increased from 0.8826, 0.9516, and 0.9061 to 0.9745, 0.9722, and 0.9778. This study provides a simple and broadly applicable strategy for optimizing high pulse repetition frequency LIBS signals and improving multi-element quantitative analysis performance.