Controlling ultrafast heat transport pathways in femtosecond laser processing via an underlying gold film

Femtosecond laser processing of multilayer films often induces significant heat-affected zone (HAZ), primarily because the coupled multi-physics heat transport mechanisms under ultrafast laser irradiation remain unclear. This study systematically investigates the role of an underlying gold film in regulating ultrafast heat transport and suppressing the HAZ by constructing a “Ni/NiO/Au/quartz” heterostructure. Combined with femtosecond laser ablation experiments and pump–probe measurements, we demonstrate that the gold film acts as an efficient thermal management medium, significantly enhancing processing quality by altering the material's phase transition pathway. Specifically, the gold film promotes a shift in the ablation mechanism from a “thermal phase transition involving the liquid phase” to “direct sublimation without the liquid phase,” reducing the characteristic HAZ width by approximately an order of magnitude. Transient reflectivity analysis indicates that the gold film effectively delays the initial electron temperature rise and the electron–phonon coupling process. More interestingly, the gold film consistently serves as an “energy coupler”, lowering the ablation threshold for Ni/NiO films of different thicknesses (50, 100, and 200 nm). This work reveals, from an ultrafast dynamics perspective, how underlying thermal design restructures energy transfer and phase transition pathways, providing a new strategy for developing low-thermal-damage ultrafast laser precision processing.