# Ultrafast laser induced structural dynamics probed by time-resolved photoelectron spectroscopy

M de Anda Villa, A Lévy, J Gaudin, R Bouillaud, D Descamps, B Dorado, N Fedorov, R Grisenti, M Hatifi, H Jouin, et al.

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M de Anda Villa, A Lévy, J Gaudin, R Bouillaud, D Descamps, et al. Ultrafast laser induced structural dynamics probed by time-resolved photoelectron spectroscopy. Journal of Physics: Conference Series, 2020, 1412 (13), pp.132025. 10.1088/1742-6596/1412/13/132025. http://hal-03943328

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Submitted on 17 Jan 2023

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Distributed under a Creative Commons Attribution 4.0 International License
Ultrafast laser induced structural dynamics probed by time-resolved
photoelectron spectroscopy

M de Anda Villa¹*, A Lévy¹†, J Gaudin², R Bouillaud², D Descamps², B Dorado³, N Fedorov²,
R Grisenti⁴, M Hatifi¹, H Jouin², E Lamour¹, S Macé¹, P Martin², S Petit², C Prigent¹,
R Sobierajski⁵, S Steydli¹, M Trassinelli¹, A Wawro⁵ and D Vernhet¹

¹Institut des Nanosciences de Paris, CNRS UMR 7588, Sorbonne Université Campus UPMC, 75005 Paris, France.

²Université de Bordeaux, CEA, CNRS, CELIA, 33400 Talence, France

³CEA, DAM, DIF, F-91297, Arpajon, France

⁴Institut für Kernphysik J.W. Goethe Universität Max-von-Laue-Str. 1, 60438 Frankfurt (M), Germany

⁵Institute of Physics of the Polish Academy of Sciences, PL-02-668 Warsaw, Poland

**Synopsis** This work aims to study laser-induced lattice dynamics when there is strong electron-lattice temperature non-equilibrium for which the material properties are poorly known. The proposed experimental technique is time-resolved photoelectron spectroscopy (Tr-PES). The main challenges of such technique are the superposition of pump and probe spectra and the distortion of the probe spectra due to the interaction with pump-induced electrons, called space charge effect (SCE). We strongly reduced this effect by tuning the 100eV XUV beamline we have developed, enabling us to investigate Copper samples.

When ultra-short laser pulses induce a non
equilibrium regime of the electron-lattice temper-
ature, theoretical description is difficult due to
the limited knowledge of material properties in
these conditions [1], including the electron-pho-
non coupling factor, the electronic and ionic ther-
mal conductivities, and the electron heat capac-
ity. In this context, time-resolved photoelectron
spectroscopy (Tr-PES) experiments may help to
improve our understanding of the physical pro-
cesses and material properties in this regime.

The excitation and relaxation of matter can be
diagnosed by studying the time evolution of their
PES spectra, which is influenced by the lattice
state/temperature. However, such a pump/probe
experiment, based on the detection of probe-in-
duced photoelectron spectra, is technically chal-
lenging due to the presence of a pump-induced
high flux of photoelectrons that can cause a loss
of information by overlapping and/or interacting
with the probe electrons, distorting the detected
spectrum (called space charge effect, SCE) [2].

To prevent the overlap of photoelectron spec-
tra, we have developed a dedicated XUV beam-
line based on High-order Harmonic Generation
[3] that delivers femtosecond pulses with the re-
quired photon energy (80 – 100 eV). This beam-
line will be fully described during the confer-
ence.

Thanks to the complete experimental and the-
oretical investigations on SCE, we have been
able to optimize the experimental parameters in
order to perform Tr-PES pump/probe experi-
ments on Copper samples where the SCE has
been strongly reduced. It allowed us to separate
the influence of lattice dynamics on the PES
from the SCE, as illustrated Figure 1.

<figure><img src="image_2.png" /><figcaption>**Figure 1.** Pump/probe measurements and their corre-
sponding SCE simulations showing the Cu PES evolution.
The difference in positive delays is attributed to the PES
modification due to lattice dynamics. Inset: spectra nor-
malized and superimposed to match the signal value of
*I* = 1/2. The signal *I* is then measured at **KE** = **87.5eV**.</figcaption></figure>

References

[1] Lin Z *et al* 2008 *Phys. Rev. B.* **77** 075133

[2] Oloff L *et al* 2016 *J. Appl. Phys. B.* **119** 225106

[3] L'Huillier A *et al* 2017 *Phys. Rev. Lett.* **70** 774

<figure><img src="image_3.png" /></figure>

<footnote>* E-mail: manuel.andavilla@insp.jussieu.fr</footnote>

<footnote>† E-mail: levy@insp.jussieu.fr</footnote>