Backward Flux Re-Deposition Patterns during Multi-Spot Laser Ablation of Stainless Steel with Picosecond and Femtosecond Pulses in Air

Abstract

We report on novel observations of directed re-deposition of ablation debris during the ultrafast laser micro-structuring of stainless steel in the air with multi-beams in close proximity on the surface. This interesting phenomenon is observed with both 10 ps and 600 fs NIR laser pulses at 5 kHz repetition rate. Ablation spot geometries could be altered with the use of beam splitting optics or a phase-only Spatial Light modulator. At low fluence (F ~ 1.0 J cm−2) and pulse exposure of a few hundred pulses, the debris appears as concentrated narrow “filaments” connecting the ablation spots, while at higher fluence, (F ~ 5.0 J cm−2) energetic jets of material emanated symmetrically along the axes of symmetry, depositing debris well beyond the typical re-deposition radius with a single spot. Patterns of backward re-deposition of debris to the surface are likely connected with the colliding shock waves and plasma plumes with the ambient air causing stagnation when the spots are in close proximity. The 2D surface debris patterns are indicative of the complex 3D interactions involved over wide timescales during ablation from picoseconds to microseconds.

Characterization of ablation conditions with the grayscale representation for Nd:YAG laser to decolor the blue‐ink on marble stone surface: Decoloration dependency on the laser flux power, wavelength, and the water spraying

“…Top panel (a): the photo-absorption assisted laser ablation mechanism and Top panel (b): the plasma-assisted laser ablation mechanism. Mechanism (a) is likely to be efficient at the low laser flux power because of the single photon event, and mechanism (b) is expected to be effective at the high laser flux power [18] . As seen in the previous figure (Figure 8), we observe an ablation effect even below 50 mJ/pulse for the short wavelength 266 nm with the F I G U R E 9 Top: The schematic images of possible mechanisms of the short-pulse laser ablation for the blue-ink stained surface.…”

Special Issue “Advanced Pulse Laser Machining Technology”

“…This Special Issue bundles together 1 review paper [ 27 ], 1 perspective article [ 28 ], and 14 original research articles [ 22 , 23 , 24 , 25 , 26 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], all focusing on the latest achievements in areas of surface and volume laser material processing, including laser-induced forward transfer and laser printing technologies [ 28 ], spatial and temporal beam shaping [ 29 , 30 , 31 , 32 ], Bessel-beam structuring of high-aspect-ratio void channels inside glass [ 34 ], direct laser interference patterning [ 35 ], pulse burst machining [ 27 ], waveguide writing [ 36 ], fs-pulse laser-induced amorphization and recrystallization of single-crystalline silicon [ 37 ], and a comparison of different beam shuttering technologies [ 33 ]—an aspect that is often neglected, but most practically relevant.…”