Transient Analysis of Laser Ablation Process With Plasma Shielding: One-Dimensional Model Using Finite Volume Method

Abstract

This paper presents a comprehensive transient model of various phenomena that occur during laser ablation of TiC target at subnanosecond time-steps. The model is a 1D numerical simulation using finite volume method (FVM) on a target that is divided into subnanometric layers. The phenomena considered in the model include: plasma initiation, uniform plasma expansion, plasma shielding of incoming radiation, and temperature dependent material properties. It is observed that, during the target heating, phase transformations of any layer occur within a few picoseconds, which is significantly lower than the time taken for it to reach boiling point (~ns). The instantaneous width of the phase transformation zones is observed to be negligibly small (<5nm). In addition, the width of the melt zone remains constant once ablation begins. The melt width decreases with an increase in fluence and increases with an increase in pulse duration. On the contrary, the trend in the ablation depth is exactly opposite. The plasma absorbs about 25–50% of the incoming laser radiation at high fluences (20-40 J/cm2), and less than 5% in the range of 5-10 J/cm2. The simulated results of ablation depth on TiC are in good agreement at lower fluences. At moderate laser fluences (10-25 J/cm2), the discrepancy of the error increases to nearly ±7%. Under prediction of ablation depth by 15% at high fluences of 40 J/cm2 suggests the possibility of involvement of other mechanisms of removal such as melt expulsion and phase explosion at very high fluences.