Time-Resolved Observation of the Ablation Plasma Plume Dynamics during Nanosecond Laser Micromachining

Fabrication of 3D microfeatures on thin metal foils using laser-induced shock pressure

“…It is also observed that the radial propagation of plasma along the surface was approximately circular even though the laser Figure 4.4: Plasma evolution at 7.3 J/cm 2 laser fluence with no confinement layer at the frame rate of 5000 fps beam was square-shaped. This behavior is consistent with the literature in which the shape of the laser-irradiated plasma plume and the shockwave were observed to be hemi-spherical while expanding both in ambient air [116,130] and in water [126]. The propagation of plasma in the axial direction has been restricted by water confinement in one direction and metal foil in the other direction.…”

“…In comparison with the literature, Tanski et al [130] observed a total plasma lifetime of 80 ns, which was slightly more than the laser pulse duration of 55 ns during UV laser irradiation of stainless steel. In their experiment, the plasma expanded until 22 ns (after the laser peak position) and then the plasma started decaying.…”

“…Typical quantitative characterization parameters include plasma plume size, plume edge position, plume velocity, and the plasma lifetime [111,130]. In most cases, the geometry of the plasma has been characterized to understand the plasma evolution behavior.…”

“…The shockwave model is based on the assumption that the plasma plume and the shockwave induced by the plume due to the differential pressure with ambient medium are propagating with identical speeds. The plume expansion corresponding to the shockfront distance (R) as a function of time (t) is given as [130],…”