Similarity in ruthenium damage induced by photons with different energies: From visible light to hard X-rays.

• Experiments show similar ablation craters in Ru caused by different fs light sources. • Absorbed energy localizes near Ru surface due to Auger electrons. • Energy localization causes thermo-mechanical ablation via stress confinement. • Damage mechanism at grazing incidence conditions does not depend on photon energy. We performed combined experimental and computational research on damage processes in ruthenium thin films induced by femtosecond lasers with various photon energies. We present an experiment with an optical laser at normal incidence conditions and compare it with previously reported experiments at grazing incidence conditions with XUV and hard X-ray photons, covering a large range of photon energies. Analysis of ablation craters in Ru shows very similar crater morphology and depth of about 10–20 nm for all considered irradiation conditions. Simulations of light-matter interactions are performed with our combined Monte Carlo and two-temperature hydrodynamics approach. The simulation results show that the primal cause of eventual ablation is Auger decay of core-shell holes created after absorption of XUV and hard X-ray photons in the vicinity of ruthenium surface. They lead to the creation of many low-energy electrons which consequently release the absorbed energy near the surface, resembling the optical irradiation case. Similar absorbed energy distributions in the top part of ruthenium induce a similar thermo-mechanical response and, therefore, similar ablation process. Our results suggest that such mechanism is universal in a wide range of photon energies at grazing incidence conditions, when the photon absorption depth is smaller than the photoelectrons range. [ABSTRACT FROM AUTHOR]