Ablation efficiency in MHz burst-mode ultrashort-pulse laser percussion drilling of thin metal foils

Gregorčič, Peter (author), Ahmed, Rida (author), Förster, Daniel (author)

The 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.

• Language: English
• Keywords: laser drilling, laser machining, MHz burst mode, ablation efficiency, ultrashort laser pulses
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 19 str.
• Numbering: Vol. 358, art. 119552
• PID: 20.500.12556/RUL-190344
• UDC: 621.9.048
• ISSN on article: 0924-0136
• DOI: 10.1016/j.jmatprotec.2026.119552
• COBISS.SI-ID: 302430211
• Publication date in RUL: 26.10.2026

Record is a part of a journal

• Title: Journal of materials processing technology
• Shortened title: J. mater. process. technol.
• Publisher: Elsevier
• ISSN: 0924-0136
• COBISS.SI-ID: 30105600

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: lasersko vrtanje, laserska obdelava, laserski bliski v nizu, učinkovitost ablacije, ultrakratki laserski bliski