On the 9th of September Igor Milov defended his PhD thesis titled “Damage processes in ruthenium thin films induced by ultrafast laser pulses” and was awarded with a “cum laude” degree. Igor performed his research in the XUV Optics group at the Faculty of Science and Technology supervised by professor Fred Bijkerk.
Igor combined various theoretical models into one hybrid approach to explain the experimentally observed damage of thin Ru films caused by ultrafast pulses. The studies were performed for various types of femtosecond light sources: optical lasers, and extreme ultraviolet (XUV) and hard X-ray free electron laser sources. Surprisingly, many similarities in damage phenomena in such a wide wavelength range were found and explained in detail.
The research was motivated by the requirement of more robust optics for high-intensity XUV and X-ray light sources. One of the complexities of such research is that experimental data on XUV- and X-ray-induced damage are difficult to obtain because of the limited access to free-electron laser facilities. The majority of data were obtained during two experimental campaigns at the Free-electron LASer in Hamburg (FLASH) performed by an international team of scientists form Poland, Czech Republic, Germany, Slovakia and the Netherlands. Thin Ru films were exposed to various doses of XUV radiation. Each exposed spot was thoroughly analyzed with various microscopy and spectroscopy techniques to determine the damage thresholds and study the details of the damage morphology.
Although optical damage of thin films is extensively studied in literature, XUV and hard X-ray induced damage is a more complex process. In the latter case high energy photons are able to ionize a target and induce electron cascades. To simulate XUV and hard X-ray damage Igor combined Monte Carlo simulations of photoabsorption and electron cascades with hydrodynamics and molecular dynamics simulations of target evolution. The simulations allowed to determine various stages of film damage and explain the details of the observed damage morphologies on a nanoscale level. The performed theoretical analysis revealed the mechanisms responsible for formation of particular surface morphologies, not only for the cases of single-pulse exposures, but also for the case of multiple pulses.