Selbstorganisierende Strukturen in der Ultrakurzpuls-Bearbeitung

For laser material processing with ultrashort pulses (USP), it is currently neither possible to make quantitative predictions about the process results prior to treatment, nor to control effects occurring in the process, such as the formation of self-organizing structures. The specific generation or prevention of these structures is of major interest from a production engineering point of view. On the one hand, related structures cause reduced structural resolution and an undesirable surface roughness, but on the other hand, changes in the surface structure can lead to beneficial properties, such as pronounced hydrophobicity.

In this project, a multi-physics model for the simulation of USP processing of metals will be developed and applied. As an intermediate goal, single pulses will be used to investigate whether a complete determination of temperature, pressure and density is possible on the basis of a transient description of the material heat fluxes and the equation of state. Furthermore, it will be analyzed whether spallation and phase explosion can be fully described by a fluid dynamic approach. The project goal is to use multipulses to investigate the formation of complex, self-assembling structures, such as cone-like protrusions (CLP) and laser-induced periodic surface structures (LIPSS). The influence of intensity changes caused by surface roughness and fluid dynamics on the formation of such structures will be determined.

The proposed project is divided into three phases. In the first phase, model development, the multiphysics USP model that is already available from the Chair of Photonic Technologies will be coupled with an absorption and heat source model that is available at the Munich University of Applied Sciences Laser Center. In addition, the equation of state and the electronic material parameters will be modelled. A model for calculating local intensity by solving Maxwell's equations will be developed and integrated. To ensure alignment and iterative model improvement, the model development will be continuously accompanied by experiments. This will lead to a very broad and accurate overview of the thermal and process-related ablation dynamics, which will form the basis of this project.

The second phase is dedicated to single pulses. Using simulation, pump-probe ellipsometry and high-speed videography, the consistency of the model descriptions will be verified, and an improvement in our understanding of the empirical process is expected. In the third phase, multipulses will be explored. Simulation, in-situ pump-probe microscopy and SEM and LSM analyses are expected to improve our understanding of empirical processes for multipulse processing. The focus will be on the influence of fluid dynamic effects on CLP and LIPSS formation and the additional influence of inhomogeneous periodic energy input caused by the interference effects of surface roughness and plasmonic effects.