Abstract
The impact of a laser pulse onto a liquid metal droplet is numerically investigated by utilising a weakly compressible single phase model; the thermodynamic closure is achieved by the Tait equation of state (EoS) for the liquid metal. The smoothed particle hydrodynamics (SPH) method, which has been employed in the arbitrary Lagrangian Eulerian (ALE) framework, offers numerical efficiency, compared to grid related discretization methods. The latter would require modelling not only of the liquid metal phase, but also of the vacuum, which would necessitate special numerical schemes, suitable for high density ratios. In addition, SPH-ALE allows for the easy deformation handling of the droplet, compared to interface tracking methods where strong mesh deformation and most likely degenerate cells occur. Then, the laser-induced deformation of the droplet is simulated and cavitation formation is predicted. The ablation pattern due to the emitted shock wave and the two low pressure lobes created in the middle of the droplet because of the rarefaction waves are demonstrated. The liquid metal droplet is subject to material rupture, when the shock wave, the rarefaction wave and the free surface interact. Similar patterns regarding the wave dynamics and the hollow structure have been also noticed in prior experimental studies.
Highlights
The continuation of Moore’s law [1], in order to meet up all the increasing demand in power efficiency, has been the main driver for the development of photolithography, which is a microfabrication process that patterns parts of a thin film aiming to make printed circuit boards
Similar findings have been published by Vinokhodov et al [24], who studied the dynamics of liquid metal droplets under ultra-short laser pulses, aiming to optimise the shape of the droplet target used in extreme Ultra Violet (EUV)
While several experiments of liquid metal droplet deformation due to a laser pulse have been performed, the only similar numerical work is of Reijers et al [8, 49], where they employed an axisymmetric Lattice-Boltzmann method to compare with the derived singlephase analytical pressure field
Summary
The continuation of Moore’s law [1], in order to meet up all the increasing demand in power efficiency, has been the main driver for the development of photolithography, which is a microfabrication process that patterns parts of a thin film aiming to make printed circuit boards. Similar findings have been published by Vinokhodov et al [24], who studied the dynamics of liquid metal droplets under ultra-short laser pulses, aiming to optimise the shape of the droplet target used in EUV. While several experiments of liquid metal droplet deformation due to a laser pulse have been performed, the only similar numerical work is of Reijers et al [8, 49], where they employed an axisymmetric Lattice-Boltzmann method to compare with the derived singlephase analytical pressure field. The SPH method within the ALE framework has been utilised in order to model the waves travelling inside the liquid metal droplet and to identify the two cavitation regimes. Validation of the numerical method is presented in S1 and S2 Appendices, whereas in S3 Appendix, the effect of the surface tension and the viscosity are investigated
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