Regensburg 2025 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 54: Ultra-fast Phenomena II
HL 54.4: Talk
Thursday, March 20, 2025, 15:45–16:00, H17
Agreement between Theoretically Predicted and Measured Bragg Peak Decay in Bismuth Following Femtosecond Laser Excitation — •Bernd Bauerhenne1, Jimiben Patel1, Sahar Bakhshi1, Sascha Epp2, and Martin Garcia1 — 1Institute of Physics, University of Kassel, Heinrich-Plett-Straße 40, D34132 Kassel, Germany — 2Max-Planck-Institut für Struktur und Dynamik der Materie, 3 Luruper Chaussee 149, 22761 Hamburg, Germany
We investigated the time-resolved Bragg peak decay in bismuth films, 30 nm and 50 nm thick, following excitation with femtosecond (fs) laser pulses. These measurements were conducted using x-ray pulses sourced from a free-electron laser. To explain the observed Bragg peak decay, we developed an electronic temperature (Te) dependent interatomic potential for bismuth, generated using forces and energies from ab initio molecular dynamics (MD) simulations at elevated Te levels. Additionally, we computed the optical properties and the Te-dependent electron-phonon coupling constant for bismuth using ab initio methods. Employing these calculated quantities, we conducted MD simulations on similarly laser-excited antimony films, 30 nm and 50 nm thick. The comparison between our theoretical predictions and experimental measurements of Bragg peak decay exhibited an agreement, affirming the accuracy of our model. This model effectively incorporates the fs-laser induced modifications of the potential energy surface and the dynamic influences of electron-phonon coupling, providing a robust framework for understanding laser-material interactions in ultrafast processes.
Keywords: bismuth; bragg peaks; ultrafast x-ray diffraction; interatomic potential; molecular dynamics simulations