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

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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.