Optimization of Laser Ablation Resistance for Multilayer Heterogeneous Thin Films Based on Optical–Thermal–Ablation Coupling and a BP Neural Network Surrogate Model

Abstract The thermophysical response of multilayer heterogeneous thin films under continuous-wave laser heating involves non-uniform volumetric heat generation modulated by interference-induced standing-wave absorption, which governs the layer-by-layer phase-change sequence and the ultimate thermal failure threshold—a coupling that conventional Beer–Lambert approximations fail to capture. This study develops an optical–thermal–ablation coupled model that resolves the standing-wave absorption profile and couples it to temperature-dependent transient heat conduction with latent-heat effects, validated against laser-damage experiments at seven power levels. A two-stage surrogate-based framework is constructed to explore the thermophysical design space in which discrete material choices and continuous layer thicknesses jointly control the absorption distribution and melting sequence. The optimal architecture is identified as SUS304/Ag/Si₃N₄/SiO₂/ITO with a refined thickness profile of 21 µm/0.106 µm/0.18 µm/2.35 µm/0.05 µm under a 25 µm total constraint, yielding a 209.6 K reduction in peak temperature relative to the baseline. The analysis reveals three thermophysical mechanisms: (i) in the interference layer, the order-of-magnitude reduction in volumetric optical absorption dominates over the 2.5-fold difference in thermal conductivity in determining the peak temperature; (ii) the positive temperature coefficient of thermal conductivity in the SUS304 substrate provides a self-regulating thermal-sink effect; and (iii) the Ag layer exhibits a non-monotonic thermal response beyond its optical saturation thickness, governed by the competition between cross-plane thermal resistance and in-plane thermal spreading coupled with absorption-peak shifting. These results clarify how interference-modulated heat generation governs phase-change sequences and thermal failure in multilayer thin films.