We report a comprehensive numerical study on laser-induced melting of copper applying the two-temperature description combined with molecular dynamics simulations (TTM-MD). It reveals the internal energy relaxation and melting dynamics of thin copper films irradiated with an ultrafast laser pulse. The TTM-MD simulations were performed utilizing different expressions for the electronic properties of copper including the temperaturedependent heat capacity and the electron-phonon coupling strength. We study the resulting melting times and structural evolution of the lattice that were found to vary in the picosecond range. The importance of the correct choice of the electron-phonon coupling parameter is underlined by its large influence on the heating and melting times of the lattice.
Laser interaction with a metal excites electrons into a non-equilibrium state after which the path back to equilibrium is determined by the scattering of electrons and phonons. We present a computational study of such a process in a metallic system showing the role of electron-phonon and phonon-phonon coupling. Our modelling approach incorporates realistic momentum resolved electron-phonon coupling in a classical molecular dynamics simulation. In addition, the phonon-phonon scattering is controlled by varying the anharmonicity of the interatomic potential. Our results show that both electron-phonon and phonon-phonon couplings are important in order to match experimental measurements.
Understanding the dynamics of electron-phonon and phonon-phonon interactions is important to unravel the complex behavior of materials subject to ultrafast laser excitation. We report the results of studying these interactions in femtosecond laser-excited tungsten (W) using the technique of ultrafast electron diffuse scattering (UEDS). By tracking changes of diffuse scattering signal over time, we resolve the dynamics of phonon populations across the Brillouin zone in W. Our results shed light on both electron-phonon and phonon-phonon coupling dynamics in W [Mo et al. Science Advances, in press (2024)]. This paper outlines the fundamental principle behind the UEDS technique, provides a brief overview of the experimental setup, and presents selected results of time-resolved diffuse scattering patterns.
Matter under extreme conditions has attracted increasing attention because of its high relevance to many areas including astrophysics, shock physics and inertial confinement fusion experiments. The capabilities of time-resolved diffraction techniques based on X-ray Free Electron Lasers and field-accelerated ultrafast electrons have allowed unprecedented explorations in this area of research, enabling femtosecond visualization of transient atomic dynamics at Ångstrom length scales. In this talk, I will present an overview of our recent work using the technique of single-shot MeV ultrafast-electron diffraction (MeV-UED) to study phase transitions and structural dynamics in ultrafast laser excited solids and liquids under warm dense conditions.
The conversion of light into chemical and mechanical energy mediates many important processes in nature, e.g. vision, photosynthesis and DNA photodamage. To understand the structure-function relationships regulating such processes one must strive to study them in their natural environment, i.e. in the liquid-phase. This presentation reports on the design of a novel Ultrafast Electron Diffraction instrument capable of resolving structural dynamics in liquid samples. The capabilities of this instrument are showcased in the study of water, where its structure was resolved up to the 3rd hydration shell with 0.6 Å spatial resolution, and dynamics were resolved with 200 fs resolution.
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