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O: Fachverband Oberflächenphysik

O 86: Ultrafast Surface Dynamics I

O 86.12: Vortrag

Donnerstag, 10. März 2016, 17:45–18:00, S052

Tracing thermal and nonthermal phase transitions in solids with pump-probe scheme. Part II: Response of optical properties — •Victor Tkachenko¹, Nikita Medvedev¹, and Beata Ziaja^1,2 — ¹CFEL at DESY, Notkestr. 85, 22607 Hamburg, Germany — ²Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Krakow, Poland

Electronic excitation and atomic dynamics after femtosecond laser pulse irradiation affect electronic structure, thus modifying optical properties of irradiated materials. During the transition of the material to non-equilibrium state and its later relaxation to a new equilibrium phase, its optical properties are influenced by both electronic and atomic dynamics. Optical coefficients can be measured in experiments and used as signatures of phase transitions. Pump-probe techniques tracing evolution of optical properties in irradiated material are modelled with our in-house developed XTANT code. As the code is a unified hybrid model that combines Monte-Carlo scheme, temperature equation, molecular dynamics technique and tight-binding formalism, it allows to trace structural transformation of diamond into graphite. The presented method proved to be feasible to evaluate complex dielectric function of the material and hence to calculate reflection, transmission and absorption coefficients of diamond at each stage of the graphitization process. Comparison with experimental data confirms the accuracy of our method.