We study the electron density response in gold after excitation with XUV and visible light. We have introduced the concept of occupational nonequilibrium and developed multiband rate equations that track the occupation in each active electron band. The rate equations also track the energy content of the sp- and d-electrons and can be coupled to the phonons. Our results show that visible light excitation leads to an overpopulation of the sp-band, driven primarily by photo-excitation, while XUV irradiation results in an underpopulation of the sp-band, dominated by subsequent impact ionization. However, assuming that the excess energy from the Auger recombination process is transferred to multiple d-electrons, we showcase that XUV-exited gold can lead to an overpopulation of the sp-band. In addition, using a detailed balance of Auger and impact ionization coefficients, we show that a single-rate relaxation time approach is sufficient to describe the imbalance between the impact ionization rate and the Auger recombination rate.
Electron-phonon coupling plays a central role in describing the energy relaxation dynamics of solids excited by ultrafast laser pulses. It depends on electronic and phononic properties in different ways for different metals. In many calculations of the electron-phonon coupling parameter, the phonons are assigned a secondary role. In this work, we study the influence of the maximum phonon energy on the electron-phonon coupling parameter within the framework of the Debye model. We find a large increase of the coupling parameter with the Debye energy for all considered metals.
When a silver sample is irradiated with an ultrashort laser pulse with a wavelength of 400 nm and 800 nm, at first only the electronic system is excited. They are driven out of equilibrium, i.e. they do not follow a Fermi-Dirac distribution directly after excitation. We calculate the transient distribution function with help of full Boltzmann collision integrals. We show the influence of laser parameters like wavelength and fluence on the initial electron nonequilibrium distribution, as well as on the thermalization process. We find an strong dependence of the excited electron distribution on characteristic features in the electronic density of states.
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