Interaction of bursts of ultrafast laser radiation in the GHz to MHz regime with metals - MULTIPULSE

研究了重复率从千兆赫兹到兆赫的超快激光脉冲与金属的相互作用，以定量解释烧蚀结构的拓扑变化和由此产生的每脉冲烧蚀体积随脉冲数目和时间距离的函数关系。此外，了解超快激光辐射与材料的相互作用，能够确定在后续项目中使用超快激光辐射脉冲有效地产生高质量结构的最佳参数。因此，通过烧蚀结构的异地分析、材料的光学响应的现场确定以及激光辐射与材料的相互作用的建模，补充地研究了所有发生的效应，例如由于来自烧蚀云的材料在材料表面上的热积累、孕育和再沉积而改变的材料表面，以及后续脉冲的激光辐射与现有等离子体或烧蚀云的相互作用(反射、透过和吸收)的相互作用。因此，计划中的项目分为三个工作包，即AP1准备、AP2双脉冲和AP3多脉冲，每个工作包都具有日益复杂和不断进步的知识。研究包括工艺和材料参数的变化(材料：以不同层厚沉积在玻璃衬底上的金和铁；激光辐射的参数：通量、脉冲持续时间、脉冲数目、时间脉冲距离)、时间和空间分辨计量的使用(泵浦-探测反射、椭圆偏振和阴影摄影)，以及激光辐射与材料相互作用的模拟(双温模型结合流体力学TTMHD、相图、激光辐射在烧蚀云中的传播)。由此，确定所施加的超快激光辐射脉冲的参数与所产生的烧蚀结构之间的关系和依赖关系。

The interaction of metals with bursts of ultrafast laser radiation with repetition rates in the gigahertz to megahertz range is investigated to quantitatively explain the change of the topology of the ablation structure and the resulting fluctuating ablation volume per pulse as a function of the number of pulses and their temporal distance. Additionally, the understanding of the interaction of the ultrafast laser radiation with the material enables the determination of optimal parameters for the efficient generation of high-quality structures using bursts of ultrafast laser radiation in follow-up projects. Therefore, all occurring effects, such as the altered material surface due to heat accumulation, incubation and re-deposition of material from the ablation cloud on the material surface as well as the interaction (reflection, transmission, and absorption) of the laser radiation of a subsequent pulse with an existing plasma or ablations cloud are complementarily investigated by an ex-situ analysis of the ablation structure, an in-situ determination of the optical response of the material, and the modeling of the interaction of the laser radiation with the material. The planned project is therefore divided into three work packages, AP1 preparation, AP2 double pulse, and AP3 multi-pulse, each with increasing complexity and progressive knowledge. The investigations include a variation of the process and material parameters (material: gold and iron deposited as layers with different layer thicknesses on a glass substrate; parameters of the laser radiation: fluence, pulse duration, number of pulses, temporal pulse distance), the use of time- and space-resolved metrology (pump-probe reflectometry, - ellipsometry and - shadow photography), and the modeling of the interaction of the laser radiation with the material (two-temperature-model in combination with hydrodynamics TTMHD, phase diagrams, propagation of the laser radiation through the ablation cloud). Thereby, the relationships and dependencies between the parameters of the applied bursts of ultrafast laser radiation with the generated ablation structures are determined.