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Sujet de stage / Master 2 Internship

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Photo-ionization of atomic/molecular gases using attosecond pulses

Contact: SALIERES Pascal, , pascal.salieres@cea.fr, +33 1 69 08 63 39
Summary:
Using the attosecond pulses produced with an intense Titanium:Sapphire laser (FAB1 of Attolab), the student will investigate the ionization dynamics of atomic and molecular gases close to resonances. The objective is to measure in real time the ejection of the electronic wavepacket and to 'see' the buildup of the resonance profile.
Possibility of continuation in PhD: Oui
Deadline for application:01/03/2018

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) with atomic or molecular 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].

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 such as photo-ionization, in order to answer questions such as: how long does it take to remove one electron from an atom or a molecule? More precisely: how long does it take for an electron wavepacket produced by absorption of an attosecond pulse to exit the atomic/molecular potential? The measurement of such tiny ionization delays is currently a “hot topic” in the scientific community. In particular, the study of the ionization dynamics close to resonances would give access to detailed information on the atomic/molecular structure, such as the electronic rearrangements in the remaining ion upon electron ejection. Recently, we have studied an auto-ionizing resonance, so-called “Fano resonance”. We have shown through 2-photon XUV+IR ionization that it is possible to observe in real time the buildup of the resonance profile [2]. The objective of the training period is to generalize the technique to the study of other types of atomic/molecular resonances, such as shape resonances. Further studies will be devoted to the possibility of controlling resonance ionization by playing on the intensity of the IR laser field superposed on the attosecond pulse.

The experimental work will include the operation of a setup installed in the FAB1 laser of Attolab allowing: i) the generation of attosecond XUV radiation, ii) its characterization using quantum interferometry, iii) its 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, and will acquire a good mastery of charged particle spectrometry. The continuation on a PhD project is advised.

References :
[1] Y. Mairesse, et al., Science 302, 1540 (2003)
[2] V. Gruson, et al., Science 354, 734 (2016)
Technics/methods used during the internship:
Intense femtosecond laser, atomic/molecular gas jets, vacuum technology, interferometry, spectrometry of XUV photons, electron spectrometry

Laboratory
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