Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 119: Non-Equilibrium Daynamics in Light-Driven Materials: Theory Meets Experiment

O 119.2: Talk

Friday, March 16, 2018, 11:45–12:00, MA 141

Relaxation of a laser-induced phonon nonequilibrium distribution — •Isabel Klett and Bärbel Rethfeld — Department of Physics and Optimas Research Center, University of Kaiserslautern, Germany

Femtosecond laser irradiation of solids leads to a thermodynamic nonequilibrium within and between the electron and phonon subsystems of the material. Due to collision processes, both subsystems relax into new thermodynamic equilibria within different respective thermalization times. In many studies, the nonequilibrium state within the phonon system is neglected and its influence on other relaxation processes is unclear. Here, we present a model for the description of the phonon nonequilibrium and its relaxation [1]. Phonon-phonon interactions are described with Boltzmann collision integrals. From this, an energy-dependent relaxation time can be extracted and inserted into a relaxation-time approach. Within the frame of this model, we study the thermalization of a nonequilibrium phonon distribution induced by ultrafast laser irradiation. It takes place on a timescale of some hundreds of femtoseconds. Additionally, we discuss the energy transfer between Fermi-distributed electrons and nonequilibrium phonons and compare this to the energy transfer between two equilibrated subsystems.

[1] I. Klett and B. Rethfeld, arXiv:1710.02355