超高速レーザー材料相互作用における異方性スパックの一般化ランジュバンダイナミクス

This work presents a computational framework for ultrafast laser ablation in metals that incorporates generalized Langevin dynamics (GLD) into the established two-temperature model-molecular dynamics (TTM-MD) approach. Unlike conventional Langevin dynamics (CLD) with uniform phonon damping, GLD introduces wavevector-dependent electron-phonon coupling, enabling anisotropic modeling of pressure-wave dynamics crucial for spallation-driven ablation. In nickel, simulations reveal up to 20% lower ablation yield along the ⟨110⟩ direction compared to ⟨100⟩ at threshold fluence, due to stronger shock attenuation and shorter phonon lifetimes. Moreover, the GLD-enhanced model, when integrated with the Helmholtz formulation for optical absorption, predicts an ablation threshold of 300 mJ/cm², consistent with experimental values (270-340 mJ/cm²). This framework reduces dependence on ad hoc parameter tuning and captures orientation-sensitive laser-matter interactions, making it well-suited for microstructure-sensitive predictions in ultrafast laser processing of polycrystalline materials.