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Attosecond imaging of electronic wavepackets in molecular gases

Contact: SALIERES Pascal, , pascal.salieres@cea.fr, +33 1 69 08 63 39
The student will generate attosecond pulses using an intense Titanium:Sapphire laser. These ultrashort pulses will be used to investigate the ultrafast ionization dynamics of molecular gases, and in particular, to image in real time the ejection of electronic wavepackets.
Possibility of continuation in PhD: Oui
Deadline for application:30/03/2022

Full description:
Recently, the generation of sub-femtosecond pulses, so-called attosecond pulses (1 as=10^-18 s), has made impressive progress. These ultrashort pulses open new perspectives for the exploration of matter at unprecedented timescale. Their generation result from the strong nonlinear interaction of short intense laser pulses (~20 femtoseconds) focused in gases. High order harmonics of the fundamental frequency are produced, covering a large spectral bandwidth in the extreme ultraviolet (XUV) range. In the temporal domain, this coherent radiation forms a train of 100-attosecond pulses [1]. The generation of isolated attosecond pulses requires shortening the fundamental laser pulses to single-cycle duration (< 5 fs) using the ‘post-compression’ technique, currently under installation at ATTOLab.

With such attosecond pulses, it becomes possible to investigate the fastest dynamics in matter, i.e., electronic dynamics that occur naturally on this timescale. Attosecond spectroscopy thus allows studying fundamental processes, e.g., photo-ionization, in order to answer questions such as: how long does it take to remove one electron from an atom or a molecule? The measurement of attosecond ionization delays is currently a “hot topic” in the scientific community. In particular, the study of the ionization dynamics close to resonances gives access to the buildup in real time of resonance profiles [2,3] and to electronic rearrangements in the ion upon electron ejection (charge migration). A recently installed spectrometer now gives access to the electron angular distribution allowing the reconstruction of the 3D movie of the electron ejection, as well as the investigation of quantum decoherence effects, e.g., induced by ion-photoelectron entanglement [4].

The experimental work will include the development/operation of a setup installed on the FAB1 laser of the ATTOLab Excellence Equipment allowing:
i) the generation of attosecond XUV pulses,
ii) their characterization using quantum interferometry,
iii) their use in photo-ionization spectroscopy (electron detection).
The theoretical aspects could also be developed. The student will be trained in ultrafast optics, atomic and molecular physics, quantum optics and will acquire a good mastery of charged particle spectrometry. The continuation on a PhD project is advised.

[1] Y. Mairesse, et al., Science 302, 1540 (2003)
[2] V. Gruson, et al., Science 354, 734 (2016)
[3] L. Barreau, et al., Phys. Rev. Lett. 122, 253203 (2019)
[4] C. Bourassin-Bouchet, et al., Phys. Rev. X 10, 031048 (2020)
Technics/methods used during the internship:
Intense femtosecond laser, high-order harmonic generation, optical and quantum interferometry, spectrometry of XUV photons, electron spectrometry

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