Abstract
The transient acoustic response of a free-standing, polycrystalline thin Au-film upon femtosecond optical excitation has been studied by time-resolved Debye–Scherrer x-ray diffraction using ultrashort Cu Kα x-ray pulses from a laser-driven plasma x-ray source. The temporal strain evolution has been determined from the transient shifts of multiple Bragg diffraction peaks. The experimental data are in good agreement with the results of calculations based on the two-temperature model and an acoustic model assuming uniaxial strain propagation in the laser-excited thin film.
Highlights
Due to the rapid progress in the development of short-pulse xray and electron sources, the field of ultrafast structural dynamics has seen dramatic progress in the last two decades (e.g., Refs. 1 and 2 and references therein)
The transient acoustic response of a free-standing, polycrystalline thin Au-film upon femtosecond optical excitation has been studied by timeresolved Debye–Scherrer x-ray diffraction using ultrashort Cu Kα x-ray pulses from a laser-driven plasma x-ray source
The experimental data are in good agreement with the results of calculations based on the two-temperature model and an acoustic model assuming uniaxial strain propagation in the laser-excited thin film
Summary
Due to the rapid progress in the development of short-pulse xray and electron sources, the field of ultrafast structural dynamics has seen dramatic progress in the last two decades (e.g., Refs. 1 and 2 and references therein). With respect to x rays, large-scale facilities such as x-ray free electron lasers (XFELs) define the current state-of-the-art, but laser-plasma based x-ray sources still represent an interesting alternative due to their simplicity, versatility, low cost, and accessibility These table-top, lab-scale sources have enabled the first ultrafast (i.e., femtosecond) time-resolved xray diffraction experiments We present the application of time-resolved Debye– Scherrer diffraction at a femtosecond laser-plasma based x-ray source for the study of structural dynamics in a thin sample, namely, the acoustic response of a 200 nm, polycrystalline Au-film upon ultrafast optical excitation. Such coherent acoustic phonons in thin films have been the subject of many studies using both time-resolved x rays The measured data are in good agreement with calculations using the two-temperature model (TTM) to estimate the time-dependent pressure/stress and an acoustic model assuming uniaxial strain wave propagation in the film
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