Laser excited metals under non-equilibrium conditions

When an ultrashort laser pulse irradiates a metal, the electron system absorbs the energy of the laser beam and is driven out of thermal equilibrium. Due to electron-electron collisions a new thermodynamical equilibrium state within the electron system is established in a characteristic time, the so-called thermalization time. Moreover, the absorbed energy of the electrons will be transferred to the phononic system. The thermalization time as well as the electron-phonon coupling strength are in the focus of experimental as well as theoretical studies. Both strongly depend on the density of states of the material and the excitation type. Furthermore, a non-thermalized electron gas couples differently to the phononic system as a thermalized one. In order to describe the relevant microscopic processes without the need to assume thermalized electrons, we apply the Boltzmann equation solving complete collision integrals. Our description gives an insight to the non-equilibrium dynamics and therefore treats the irradiation and relaxation microscopically in contrast to a simple two temperature approach. To describe realistic materials we implement the density of states in our approach and extract electron thermalization time and electron-phonon coupling under non-equilibrium conditions. As a result of our simulations, both, the thermalization time and the electron-phonon coupling depend on the density of states and on the excitation strength.