Quantitative Untersuchung des Laserablationsprozesses mittels Kombination von optischer Spektroskopie und Massenspektrometrie

This dissertation assesses the process of laser-induced ablation using picosecond laser pulses by applying it to different materials. The introduction reviews the theoretical background of the different ablation mechanisms, which are classified according to the used laser parameters. Following that, the ablation is characterized by employing various experimental methods: the crater formation resulting from successive ablation and the material-depending ablation rates are determined by analyzing the crater structures. Moreover, an experimental setup for the study of laser-induced ablation in vacuum, which has been built in the course of this work, is presented. This setup enables the simultaneous appliance of mass spectrometry and complementary optical spectroscopy. The analyses of a thin film solar cell and a C/Ti/Mo-layer structure demonstrate that depth-resolved sample characterization is possible with laser-induced ablation using picosecond pulse durations. Results show that the ablation rates within one sample layer are proportional to the applied pulse energy. In spite of the short pulse duration of τ$_{L}$ = 35 ps, thermal effects are observed in the ablation process: the crater size depends on the laser pulse energy and material is redeposited around the crater in the laser-induced ablation process. Laser parameters like pulse energy and diameter are optimized for the determination of hydrogen content in fusion-relevant materials via a residual gas analysis and a simultaneously performed laser-induced breakdown spectroscopy. An investigation of the laser-induced fragmentation of an amorphous hydrogenated carbon layer (a–C:H) shows that one third of the total hydrogen content is found in hydrocarbons after ablation. This needs to be included in a quantitative sample analysis. For the first time, the depth-resolved hydrogen content in graphite tiles, which were exposed in the fusion test facility Wendelstein 7-X, could be measured quantitatively in ex-situ analysis. The integrated signals show good agreement with thermal desorption spectroscopy measurements. Aiming at applying the developed measurement technique in a future fusion reactor, first results of deuterium retention analyses in graphite and tungsten are presented. These show particle densities in the order of 10$^{19}$ $^{D}$ $^{Atome/_{cm}}$ $^{3}$ vorgestellt

Quantitative Untersuchung des Laserablationsprozesses mittels Kombination von optischer Spektroskopie und Massenspektrometrie

In der vorliegenden Arbeit wird der laserinduzierte Ablationsprozess mittels Pikosekundenpulsen für verschiedene Materialien untersucht. Hierzu werden unterschiedliche Ablationsmechanismen in Abhängigkeit von den Laserparametern zunächst theoretisch erläutert. Experimentell werden die sukzessive Ablation und die Abtragraten über Vermessungen von Kraterstrukturen untersucht. Zudem wird ein im Zuge dieser Arbeit entwickelter Versuchsaufbau zur laserinduzierten Ablation im Vakuum vorgestellt. Dieser ermöglicht eine sich ergänzende simultane Ausführung von Massenspektrometrie und optischer Spektroskopie. Es konnte hierbei erstmalig der tiefenaufgelöste Wasserstoffgehalt in Graphitziegeln, exponiert im Fusionsexperiment Wendelstein 7-X, ex-situ quantitativ ermittelt werden. Für eine potentielle zukünftige Anwendung der entwickelten Messmethode in Fusionsreaktoren werden weiterhin Analysen der Deuteriumrückhaltung in Graphit und Wolfram vorgestellt