Thermo-elasto-plasto-dynamics of ultrafast optical ablation in polycrystalline metals. Part II: Response and damage evaluation

Abstract

Ablation dynamics focusing exclusively on the thermal field without also considering electron emission and thermal stress is incomplete. The thermo-elasto-plastodynamic model developed in Part I of the paper is applied to estimate non-thermal ablation and the onset of fracture in a polycrystalline gold material in response to ultrafast irradiation of low fluence. Non-thermal ablation in the polycrystalline gold material is a complex dynamical process involving incident fluence, material thermophysical properties, and grain size as the primary parameters. Lattice temperatures are found to be persistently lower than the melting temperature of the target material, thus implying material removal, i.e., ablation, by ways of phase transition and phase explosion is physically improbable. The mechanism that underlies thermally induced damage modes such as yielding, layer disintegration, fragmentation, fracture, and ejection is investigated by exploring the induced thermal stress, elastic-plastic deformation, and strain energy density rate. The concept of power density is applied to estimate ablation depth and the time instance at which yielding and subsequent non-thermal ablation are initiated.

Keywords:

• Ablation depth
• low fluence ultrafast laser
• nonlinear hardening
• non-melting ablation
• power density
• thermo-elasto-plasto-dynamics