Generalized Langevin dynamics for anisotropic spallation in ultrafast laser-material interactions

MM Hayder and S Chowdhury and V Athmanathan and KA Rahman, OPTICS EXPRESS, 33, 50108-50122 (2025).

DOI: 10.1364/OE.571421

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. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

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