The interaction of nanosecond laser pulses with metallic materials involves multiple complex physical processes, and constructing a self-consistent model capable of uniformly describing all stages remains a significant challenge. This work establishes a multi-physics coupled model for pure iron, encompassing laser energy deposition, solid-liquid phase transition, gas-liquid interfacial kinetic transport, plasma expansion and ionization, and spectral radiation. The numerical solution employs a partitioned approach, utilizing an implicit compact difference scheme for the target region and a Mac-Cormack explicit scheme for the ambient atmosphere, to simulate the ablation dynamics.
The simulations elucidate the emergence of plasma shielding and its inhibitory effect on the evaporation process. They confirm that the early-stage ablation products are primarily transported via a supersonic expansion mode, which accounts for 81.6% of the total ablated mass transfer. The model successfully captures the complete evolution of the plasma plume from a high-temperature, highly ionized state (dominated by Fe³⁺) to a low-temperature, neutral atomic state (dominated by Fe⁰). Based on this, spectral calculations demonstrate the dynamic evolution of radiative characteristics from an early stage featuring a “strong continuum background dominated by ion lines” to a later stage where “the continuum attenuates, atomic lines become prominent, and self-absorption appears”. The emergence of self-absorption proves the model’s capability to effectively capture the optical thickness effects arising from spatial inhomogeneity within the plasma.
Through systematic comparison with experimentally measured spectra and calculated results from the PrismSPECT and NIST LIBS spectral programs, the model presented here achieved the highest comprehensive scores in quantitative evaluations across multiple channels. This validates the necessity and superiority of the full-chain self-consistent modeling approach over traditional methods relying on spatial averaging or the optically thin approximation, particularly in describing plasma inhomogeneity and radiation transport. It also provides a numerical simulation framework for applications such as laser processing parameter optimization, quantitative spectroscopic analysis, and the design of novel plasma light sources.