Intensive ultrashort lasers have become effective tools that are used to modify optical, mechanical and chemical properties of materials at the surface and in the bulk. Examples include applications in catalysis, photonics, and biomedicine. Alternatively, apart from such controlled and desired altering of material properties, intensive lasers may cause unwanted material damage. It is crucial to avoid such laser-induced damage, for example, in optical elements such as lenses, mirrors or transmission filters at various laser facilities such as EUV and X-ray free electron lasers.

In this work, we investigate the mechanisms of femtosecond laser interaction with metal thin films, with the main focus on ruthenium as a material used as grazing incidence mirror in EUV and X-ray optics [1]. We analyze damage experiments performed with various light sources ranging from optical lasers to EUV and hard X-ray free-electron lasers, finding a surprising similarity in damage crater morphology [2]. Our experimental studies are combined with theoretical modelling of laser-induced processes to explain the observed phenomena. For that, we developed a hybrid model based on Monte Carlo, two-temperature model, and molecular dynamics techniques. Additionally, we explore a topic of ultrafast laser-induced phase transitions in metals and the interplay of thermal and non-thermal effects in such transitions [3].

[1] I. Milov, V. Zhakhovsky, D. Ilnitsky, K. Migdal, V. Khokhlov, Yu. Petrov, N. Inogamov, V. Lipp, N. Medvedev, B. Ziaja, V. Medvedev, I. Makhotkin, E. Louis, F. Bijkerk, Two-level ablation and damage morphology of Ru films under femtosecond extreme UV irradiation , Appl. Surf. Sci. 528, 146952 (2020)
[2] I. Milov, V. Lipp, D. Ilnitsky, N. Medvedev, K. Migdal, V. Zhakhovsky, V. Khokhlov, Yu. Petrov, N. Inogamov, S. Semin, A. Kimel, B. Ziaja, I. Makhotkin, E. Louis, F. Bijkerk, Similarity in ruthenium damage induced by photons with different energies: From visible light to hard X-rays , Appl. Surf. Sci. 501, 143973 (2020)
[3] N. Medvedev, I. Milov, Nonthermal phase transitions in metals , Sci. Rep. 10(1), 1-9 (2020)