Abstract The ablation of thin metal films using ultrafast laser radiation represents a standard processing procedure in laser technology. However, looking closer to the resulting structures, the arising topology deviates strongly from the expected one. Ablation of thin gold films using ultrafast laser radiation with a Gaussian-shaped spatial intensity distribution results in flat topologies. By synergistically combining space and time-resolved reflectometry with expanded two-temperature hydrodynamic modeling, we explain the formation of bulging and rupture of the thin film-surface by the expansion of strongly stretched liquid material due to the induced rarefaction wave propagating towards the substrate. Also, the formation of a flat ablation structure is described by the interplay of two rarefaction waves, one propagating towards the substrate and the other one propagating towards the vacuum boundary, within the completely molten film. The simulated topology agrees excellent with the experimentally observed ablation structure. Besides, all simulated stages of excitation of the gold film, namely electron-phonon non-equilibrium, hydrodynamic expansion, and rupture, are confirmed by space and time-resolved pump-probe reflectometry.

中文翻译：

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超快激光诱导金薄膜烧蚀的流体动力学建模和时间分辨成像反射计

摘要 使用超快激光辐射烧蚀金属薄膜代表了激光技术中的标准加工程序。然而，仔细观察所产生的结构，出现的拓扑结构与预期的拓扑结构有很大的不同。使用具有高斯形空间强度分布的超快激光辐射烧蚀薄金膜会产生平坦的拓扑结构。通过将空间和时间分辨反射计与扩展的双温度流体动力学模型相结合，我们解释了由于诱导的稀疏波向基板传播而导致强烈拉伸的液体材料膨胀导致薄膜表面膨胀和破裂的形成。此外，平坦消融结构的形成是通过两个稀疏波的相互作用来描述的，在完全熔化的薄膜内，一种向基板传播，另一种向真空边界传播。模拟拓扑与实验观察到的烧蚀结构非常吻合。此外，金膜的所有模拟激发阶段，即电子-声子非平衡、流体力学膨胀和破裂，都通过空间和时间分辨泵浦探针反射测量法得到证实。