Mechanisms of ultrafast GHz burst fs laser ablation

Minok Park; Yueran Gu; Xianglei Mao; Costas P Grigoropoulos; Vassilia Zorba

doi:10.1126/sciadv.adf6397

Mechanisms of ultrafast GHz burst fs laser ablation

Sci Adv. 2023 Mar 22;9(12):eadf6397. doi: 10.1126/sciadv.adf6397. Epub 2023 Mar 22.

Authors

Minok Park^{1

2

3}, Yueran Gu^{1

3}, Xianglei Mao¹, Costas P Grigoropoulos^{2

3}, Vassilia Zorba^{1

3}

Affiliations

¹ Laser Technologies Group, Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
² Laser Thermal Laboratory, Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA 94720-1740, USA.
³ Department of Mechanical Engineering, University of California at Berkeley, Berkeley, CA 94720-1740, USA.

Abstract

Gigahertz (GHz) femtosecond (fs) lasers have opened possibilities for enhancing and controlling the laser machining quality to engineer the physicochemical properties of materials. However, fundamental understanding of laser-material interactions by GHz fs laser has remained unsolved due to the complexity of associated ablation dynamics. Here, we study the ablation dynamics of copper (Cu) by GHz fs bursts using in situ multimodal diagnostics, time-resolved scattering imaging, emission imaging, and emission spectroscopy. A combination of probing techniques reveals that GHz fs bursts rapidly remove molten Cu from the irradiated spot due to the recoil pressure exerted by following fs pulses. Material ejection essentially stops right after the burst irradiation due to the limited amount of remnant matter, combined with the suppressed heat conduction into the target material. Our work provides insights into the complex ablation mechanisms incurred by GHz fs bursts, which are critical in selecting optimal laser conditions in cross-cutting processing, micro/nano-fabrication, and spectroscopy applications.