Expansion and Fragmentation of a Liquid-Metal Droplet by a Short Laser Pulse
Abstract
We report on an experimental and numerical study of the fragmentation mechanisms of a micrometer-sized metal droplet irradiated by ultrashort laser pulses. The results of the experiment show that the fast one-side heating of such a droplet may lead to either symmetric or asymmetric expansion followed by different fragmentation scenarios. To unveil the underlying processes leading to fragmentation, we perform simulations of liquid-tin droplet expansion produced by initial conditions similar to those in an experiment using the smoothed particle hydrodynamics (SPH) method. Simulations demonstrate that a thin heated surface layer generates an ultrashort shock wave propagating from the frontal side to the rear side of a droplet. Convergence of such a shock wave followed by an unloading tail to the droplet center results in cavitation of material inside the central zone, caused by the strong tensile stress. Reflection of a shock wave from the rear side of a droplet produces another region of highly stretched material where spallation may occur, producing a thin spall layer moving with a velocity higher than the expansion rate of the liquid shell around the central cavity. It is shown both experimentally and numerically that the threshold laser intensity necessary for the spallation is higher than the threshold required to induce cavitation close to the droplet center. Thus, the regime of asymmetrical expansion is realized if the laser intensity exceeds the rear-side spallation threshold. The transverse and longitudinal expansion velocities obtained in SPH simulations of different expansion regimes agree well with our experimental data.
- Publication:
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Physical Review Applied
- Pub Date:
- December 2018
- DOI:
- 10.1103/PhysRevApplied.10.064009
- arXiv:
- arXiv:1807.01862
- Bibcode:
- 2018PhRvP..10f4009G
- Keywords:
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- Physics - Computational Physics;
- Physics - Applied Physics
- E-Print:
- Phys. Rev. Applied 10, 064009 (2018)