Transient Multi-Phase Modelling of Process Dynamics in Ultrafast Laser Ablation of Metals

在超快激光系统在工业生产中的应用日益广泛和激光制造技术过程模拟取得最新进展的背景下，本课题将开发一个金属超快激光烧蚀的数值多相模拟模型，该模型将利用纳米、皮、飞秒激光脉冲对烧蚀和结构过程的瞬态动力学进行成像。研究工作分为四个工作包，这些工作包相互建立。基于对超短激光脉冲与金属相互作用过程中吸收、热传导和烧蚀过程的数值描述的初步发展，应考虑完整的结构过程。在描述超短激光脉冲在工件表面、材料体积和发生的等离子体中的吸收时，除了考虑随温度变化的光学性质外，还特别关注非线性吸收现象的建模。为了描述超短激光脉冲与金属相互作用过程中的热过程，应考虑热材料性质中的潜热和温度依赖性，建立基于双温度模型的热传导模拟。材料烧蚀的建模重点是在不同脉冲持续时间和影响区域的定量正确烧蚀体积。从烧蚀过程的不可压缩描述出发，在模拟中应实现蒸发和等离子体形成的可压缩-不可压缩耦合多相模型。最后，在建立的模型的基础上，考虑具有脉冲序列的复杂结构过程，以成像处理参数（脉冲持续时间、影响度、波长、脉冲重复率）对过程和处理结果的影响。这些调查伴随着广泛的实验分析，为模型开发提供数据库和过程知识。此外，它们还用于验证所开发的模型。为了表征不同脉冲时间和激光波长下铁和铜的烧蚀过程以及可实现的结构质量和烧蚀效率，建立了应使用仿真模型。在对光束与物质相互作用过程进行基础研究的基础上，确定了超短激光脉冲结构的最佳加工参数和加工策略。该仿真模型将为未来工业超快激光结构中基于仿真的工艺布局和规划奠定基础。

At the background of an increasing application of ultrafast laser systems in industrial production and latest progress in process simulation of laser based manufacturing techniques in the frame of the research project a numerical multi-phase simulation model for ultrafast laser ablation of metals, that images the transient dynamics of ablation and structuring processes with nano-, pico- and femtosecond laser pulses, shall be developed.The research effort is structured in four work packages that build up on one another. Based on the initial development of a numerical description for the absorption, heat conduction and ablation processes during the interaction of ultrashort laser pulses with metals, complete structuring processes shall be regarded. In the description of the absorption of ultrashort laser pulses on the surface of the workpiece, in the material volume and in the occurring plasma, besides a consideration of the changing optical properties with the temperature special focus lies on the modeling of nonlinear absorption phenomena. For the description of thermal processes during the interaction of ultrashort laser pulses with metals a heat conduction simulation based on the two-temperature model shall be developed, taking into account latent heats and temperature dependences in the thermal material properties. The modeling of the material ablation focuses on quantitative correct ablation volumes in the different pulse duration and fluence regions. Emanating from an incompressible description of the ablation process, a coupled compressible-incompressible multi-phase model for evaporation and plasma formation shall be implemented in the simulation. Finally, based on the developed model complex structuring processes with pulse sequences shall be regarded in order to image the influence of processing parameters (pulse duration, fluence, wavelength, pulse repetition rate) on the process and the processing result. These investigations are accompanied by extensive experimental analyses delivering the database and process knowledge for the model development. Besides, they serve for a verification of the developed models.The simulation model shall be used in order to characterize ablation processes of iron and copper with different pulse durations and laser wavelengths with respect to achievable structuring quality and ablation efficiency. Building up on a fundamental investigation of the beam-matter interaction processes, optimal processing parameters and processing strategies for the structuring with ultrashort laser pulses shall be identified. The simulation model shall set the base for a future simulation based process layout and planning in industrial ultrafast laser structuring.