5-axis ultrafast laser drilling with burst mode

Recently, major laser manufacturers have introduced MHz- and GHz-burst mode capabilities, where each primary laser pulse is subdivided into a series of lower peak power pulses that collectively sum to the same energy as a single pulse. While experimental studies suggest that burst mode can improve ablation efficiency for select materials—particularly those with reduced free-electron density—there is limited evidence for its efficacy for metal machining. This work benchmarks short GHz-burst pulse groups against single pulse mode in 5-axis ultrafast laser micromachining, specifically evaluating the different effects on blind hole drilling in stainless steel. Recent findings [Belski, SPIE Proc. 13351, 109–118 (2025)] demonstrate that a position-based pulse control mechanism, wherein the number of pulses emitted per spatial location is precisely controlled, significantly enhances ablation efficiency. By allowing a predefined number of pulses (e.g., 1, 5, 10, or 20) at each position-based firing event, material removal rates can be optimized while maintaining high-quality hole characteristics, including controlled sidewall taper, minimal surface charring and smooth bottom surface finish. This controlled approach is functionally analogous to burst mode, where pulse packets enable deeper penetration and faster material removal without increasing the average power. A next logical step is to conduct a similar test using burst modes provided by laser manufacturers. By directly comparing burst mode with single pulse mode under identical machining conditions, this study quantifies trade-offs between processing efficiency and feature quality. Blind holes serve as an ideal test case, allowing detailed examination of entrance edge integrity, sidewall formation and floor smoothness as key quality metrics. While previous studies primarily report either efficiency [Hodgson et al., SPIE Proc. 11673, 21–41 (2021); Cheng et al., Optics Laser Technol. 46, 88–102 (2013)] or quality [Lei et al., J. Manuf. Sci. Eng. 142, 031005 (2020); Jahns et al., Phys. Procedia 41, 630–635 (2013); Mincuzziet al., Optics Lasers Eng. 118, 52–57 (2019)], this work seeks to establish an understanding of their interplay in a controlled 5-axis micromachining environment.