Spatio-temporal ablation dynamics and plasma chemistry of aluminum induced by temporally modulated ytterbium fiber laser

Abstract

In this work, we studied single-pulse ablation dynamics of temporally modulated continuous wave laser-material interaction with Al using in situ multimodal time-resolved diagnostics, that describe in detail the associated physical and chemical processes. Timeresolved scattering, emission imaging, and optical emission spectroscopy unveiled a sequence of events spread out across three distinct phases: (i) early phase ablation process, associated with particle generation and liquid Al columns formation (< 20 μs), (ii) secondary detonation when sufficient ejected material is accumulated over the surface (20-50 μs), and (iii) molten liquid Al pool oscillation on the surface, followed by large droplet ejection from the liquid pool (100-500 μs). Atomic Al and AlO were observed with optical emission spectroscopy at different ratios during the entire lifetime of the event, verifying the formation of oxidized Al vapor upon its interaction with air. Morphological and compositional characterization confirmed surface oxidation and material resolidification in the form of protrusions produced during the irradiation process. This work provides insights into the complex physical and chemical mechanisms of single-pulse ablation in the sub-millisecond laser pulse regime, which are critically important for parameter optimization in a variety of laser processing, microfabrication, and deposition applications.

Mechanisms of ultrafast GHz burst fs laser ablation

“…5B ). Such disturbances were observed in laser-induced melting of metals due to hydrodynamic instabilities ( 22 ), which further supports the argument that ablation by GHz bursts with 200 pulses involves fluidic transport. In addition, the GHz burst with 200 pulses resulted in a longer ejection duration (<300 ns) from the surface than the GHz burst with 50 pulses (<100 ns).…”

“…S12). Such formations were experimentally probed when the liquid-phase expulsion via recoil pressure contributed to the material removal in the case of liquid aluminum ablation under quasi-CW illumination ( 22 ).…”

“…A detailed description of the experimental system is given in Materials and Method, while information on the Mie theory modeling (21) used to design the scattering imaging system is included in figs. S2 and S3 (22,23).…”

Mechanisms of graphite ablation by sub-millisecond ytterbium fiber laser pulses

“…In the case of aluminum (Al) irradiated under identical conditions, particles observed at ~ 2 μs gate delay were produced from the breakup of ejected liquid column jets when high kinetic energy overcame surface tension. 13 However, we could not observe such liquid material ejection for the case of graphite under single sub-millisecond pulse irradiation. Instead, particles were directly expelled from the bulk substrate (side imaging in Fig.…”

“…Temporally modulated continuous wave (quasi-CW) fiber lasers were recently introduced as means to machine graphite at large ablation depths via single pulse irradiation 11 , which translates to rapid processing rates. More importantly, the resulting ablation features on graphite are well-defined, free of undesirable burrs or resolidified/deposited residues which are spontaneously formed during the prolonged laser-material interaction in metals [12][13][14][15][16] . However, the origin of this behavior remains unknown.…”