Personal web page : http://iramis.cea.fr/Pisp/pascal.salieres/
Laboratory link : http://iramis.cea.fr/LIDYL/ATTO/
More : http://attolab.fr/
Using tunable attosecond pulses produced with an optical parametric amplifier (OPA) pumped by an intense Titanium:Sapphire laser (ATTOLab Excellence Equipment), the student will investigate the ionization dynamics of atomic and molecular gases close to resonances. The objective is to follow in real time the electron ejection and to measure the buildup of the resonance profile.
Detailed summary :
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 infrared (IR) 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 .
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 .
The objective of the thesis is to generalize the technique to the study of other types of atomic/molecular resonances, such as shape resonances. To this end, tunable attosecond pulses will be generated using the mid-IR [1.2-2µm] radiation from an optical parametric amplifier (OPA) pumped by an intense Titanium:Sapphire laser. Finally, the measurement of the photoelectron angular distribution, in combination with the temporal information detailed above, will allow the reconstruction of the full 3D movie of the electron ejection.
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 will also be developed. The student will be trained in ultrafast optics, atomic and molecular physics, quantum chemistry, and will acquire a good mastery of charged particle spectrometry. A background in ultrafast optics, nonlinear optics, atomic and molecular physics is required.
Part of this work will be performed in collaboration with partner French laboratories (ANR CIMBAAD) and members of the MEDEA European Network through joint experiments in the different associated laboratories (Milano, Lund).
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