Ablation efficiency in MHz burst-mode ultrashort-pulse laser percussion drilling of thin metal foilsGregorčič, Peter (Avtor) Ahmed, Rida (Avtor) Förster, Daniel (Avtor) laser drillinglaser machiningMHz burst modeablation efficiencyultrashort laser pulsesThe increasing average power of ultrashort-pulse lasers requires efficient use of the available pulse energy, and MHz burst operation offers one route by distributing this energy among temporally separated sub-pulses. However, systematic understanding of how ablation efficiency evolves with the number of pulses per burst, N$_{p}$, during percussion drilling of thin metal foils remains limited. Therefore, we investigate how the maximum depth-based ablation efficiency, η$_{max}$, evolves with N$_{p}$ up to 40 during MHz burst-mode percussion drilling of 50-µm-thick metal foils using 300-fs, 1030-nm laser pulses. Measurements for stainless steel (SS) and Ti are compared with those for Al and Cu, with thermal diffusivities approximately one order of magnitude higher. We separate η$_{max}$ into two contributions: the optimum sub-pulse fluence, F▫$_{b}^{opt}$▫, and the average ablation depth per sub-pulse, Δd$_{b}$. A simple theoretical model describes how residual heat accumulation affects F▫$_{b}^{opt}$▫, while the logarithmic ablation-depth law is extended phenomenologically to describe deviations from additive depth scaling. For SS and Ti, F▫$_{b}^{opt}$▫ decreases with N$_{p}$, in agreement with the baseline predicted by the model, while moderately super-additive depth scaling produces a strong initial increase in η$_{max}$; at higher N$_{p}$, η$_{max}$ reaches more than 470% above the single-pulse value. Al and Cu deviate from this baseline through an initial increase in F▫$_{b}^{opt}$▫ and pronounced odd-even modulation of Δd$_{b}$ and η$_{max}$. These departures are consistent with additional plume-mediated attenuation and re-deposition reported in the literature. At larger N$_{p}$, the decrease in Δd$_{b}$ and increasingly melt-dominated morphology coincide with diminishing further gains in η$_{max}$, consistent with melt redistribution and plume-mediated attenuation.20262026-10-26 09:48:17Članek v reviji190344UDK: 621.9.048ISSN pri članku: 0924-0136DOI: 10.1016/j.jmatprotec.2026.119552COBISS_ID: 302430211sl