Makhotkin, I.; Milov, I.; Chalopsky, J.; Tiedtke, K.; Enkisch, H.; se Vries, G.; Scholze, F.; Siewert, F.; Sturm, J.; Nicolaev, K.; van de Kruijs, R.; Smithers, M.; van Wolferen, H.; Keim, E.; Louis, E.; Jacyna, I.; Jurek, M.; Klinger, D.; Pelka, J.; Juha, L.; Hajkova, V.; Vozda, V.; Burian, T.; Saksl, K.; Faatz, B.; Keitel, B.; Plönjes, E.; Schreiber, S.; Toleikis, S.; Loch, R.; Hermann, M.; Strobel, S.; Donker, R.; Mey, T.; Sobierajski, R.: Damage accumulation in thin ruthenium films induced by repetitive exposure to femtosecond XUV pulses below the single-shot ablation threshold. Journal of the Optical Society of America / B 35 (2018), p. 2799-2805
Open Accesn Version

The process of damage accumulation in thin ruthenium films exposed to multiple femtosecond XUV free electron laser (FEL) pulses below the critical angle of reflectance at the Free electron LASer facility in Hamburg (FLASH) was experimentally analyzed. The multi-shot damage threshold is found to be lower than single-shot damage threshold. Detailed analysis of the damage morphology and its dependence on irradiation conditions justifies the assumption that cavitation induced by the FEL pulse is the prime mechanism responsible for multi-shot damage in optical coatings.