Abstract Sapphire is widely used in civilian and military equipment owing to its superior optical and mechanical properties. Femtosecond laser has been demonstrated to be an effective tool to process sapphire material. However, the direct processing of sapphire by femtosecond laser still meets some challenges, such as poor ablation morphology and low laser energy absorption. In this work, femtosecond laser processing of sapphire coated with a 12-nm-thick gold film (Au-coated sapphire) has been investigated. The experimental results have revealed that the ablation morphology of Au-coated sapphire has been improved, featuring fewer molten materials and thermal cracks, as well as regular crater shape and uniform periodic surface structures. It has also been found that, under 100 shots condition, the threshold fluence of Au-coated sapphire is reduced by about 56% compared to that of uncoated one. Meanwhile, the incubation effect of Au-coated sapphire is stronger than that of uncoated one. We also illustrate that the material removal rate of Au-coated sapphire is increased up to about two times higher than that of uncoated one. In order to reveal the effective mechanism of the gold film in the laser processing of sapphire, the energy transfer process among incident photons, free electrons and sapphire lattice phonons was studied. Our study provides a guidance for improving the laser ablation capacity of sapphire.

中文翻译：

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金膜辅助飞秒激光加工提高蓝宝石烧蚀能力

摘要 蓝宝石以其优越的光学和机械性能被广泛应用于民用和军用设备中。飞秒激光已被证明是加工蓝宝石材料的有效工具。然而，飞秒激光直接加工蓝宝石仍面临一些挑战，如烧蚀形态差和激光能量吸收低。在这项工作中，研究了用 12 纳米厚的金膜（镀金蓝宝石）对蓝宝石进行飞秒激光加工。实验结果表明，镀金蓝宝石的烧蚀形貌得到了改善，熔融材料和热裂纹更少，陨石坑形状规则和均匀的周期性表面结构。还发现，在 100 次射击条件下，与未涂层蓝宝石相比，Au 涂层蓝宝石的阈值能量密度降低了约 56%。同时，镀金蓝宝石的孵化效果强于未镀膜的蓝宝石。我们还说明镀金蓝宝石的材料去除率比未镀膜蓝宝石的材料去除率提高了大约两倍。为了揭示金膜在蓝宝石激光加工中的有效机理，研究了入射光子、自由电子和蓝宝石晶格声子之间的能量传递过程。我们的研究为提高蓝宝石的激光烧蚀能力提供了指导。我们还说明镀金蓝宝石的材料去除率比未镀膜蓝宝石的材料去除率提高了大约两倍。为了揭示金膜在蓝宝石激光加工中的有效机理，研究了入射光子、自由电子和蓝宝石晶格声子之间的能量传递过程。我们的研究为提高蓝宝石的激光烧蚀能力提供了指导。我们还说明了镀金蓝宝石的材料去除率比未镀膜蓝宝石的材料去除率提高了大约两倍。为了揭示金膜在蓝宝石激光加工中的有效机制，研究了入射光子、自由电子和蓝宝石晶格声子之间的能量传递过程。我们的研究为提高蓝宝石的激光烧蚀能力提供了指导。