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Sujet de stage / Master 2 Internship

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Generation of attosecond pulses in transient gratings

Contact: RUCHON Thierry, , thierry.ruchon@cea.fr, +33 1 69 08 70 10
During this training, the student will set up, on an intense femtosecond laser, an interferometric device to study, during the generation of attosecond pulses, the couplings between angular orbital moment and spin angular moment of light. This experimental training will require concepts of nonlinear optics, quantum optics and laser-matter interaction.
Possibility of continuation in PhD: Oui
Deadline for application:31/05/2018

Full description:
In recent years, the generation of sub-femtosecond pulses, so-called attoseconds (1as = 10-18s), has seen spectacular progress. These ultra-short pulses open up new prospects for the exploration of matter on a previously inaccessible scale of time. Their generation is based on the highly nonlinear interaction of short (10 to 50 femtosecond) intense laser pulses with atomic or molecular gases. The high-order harmonics of the fundamental frequency are produced over a wide spectral range (160-10 nm) covering the extreme ultraviolet spectral range (UVX). In the temporal domain, this coherent radiation appears as a train of light pulses lasting some 100 attoseconds [Mairesse03]. One way of applying these pulses is their use in pump-probe schemes. A gas sample is brought into an excited state by a first IR pulse and a second attosecond pulse, is shine at an adjustable delay, less than one femtosecond later. The attosecond pulse having a spectrum in the XUV it photoionizes the samples. There are thus two ways of "reading" the interaction: by analyzing the defect of transmitted photons or the photoelectrons emitted. Until now, these techniques have been used by probing the material with linearly polarized attosecond radiation having a cylindrical symmetric wavefront. Recently, we have extended the range of these experiments using, on the one hand, circularly polarized pulses [Ferré15] and, on the other hand, pulses whose wave front is helical [Géneaux16, Gauthier17]. While the former are associated with photons carrying an angular spin moment, the latter correspond to photons carrying an orbital angular momentum. The prospects are both applied, in particular to the femtochemistry of chiral molecules, and fundamental, in particular related to the laws of conservation of angular moments in the processes of nonlinear optics.

During this training, we propose to set up a unique optical device to test the laws of conservation of the angular momenta during the extremely nonlinear phenomenon at the base of the synthesis of attosecond pulses, the generation of high order harmonics (HHG). We will use two femtosecond (≃ 25 fs) intense beams, which will intersect in an atomic gas where the HHG will take place. At this point, the two beams will form a transient grating whose thickness and depth will be adjustable. Each of the two beams will carry an angular moment of spin and / or an orbital angular moment, adjustable rapidly. The diagnosis of the interaction will be carried out by both polarimetry of the XUV radiation and by measurement of the orbital angular momentum by interferometry. In addition to the fundamental aspects involved, the development of this technique will open new fields of investigation, such as the study of birefringences or transient attosecond dichroism which will give a new image of the processes at work in asymmetric systems at this time scale. This source ionizing any material, dichroisms will also be detectable on the asymmetries of electron yields in charged particle detectors (VMIS). This second path of analysis, which we have recently begun to explore [Gruson16], will require specific experimental developments that would take place within the framework of a Phd thesis. This traingin will be hosted on Attabab FAB1 & 10 lasers

Acquired know-hows:

The trainee will acquire a practice of femtosecond lasers and charged particle spectrometry techniques. He or she will also study strong fields physics on which the high harmonic generation is based. Finally, theoretical developments may also be included depending on the candidate's tastes. The pursuit in PhD thesis is desired.

Required skills:
Skills in optics, atomic and molecular physics will be appreciated.

References :
[Ferré15] Ferré, A. et al.: , 2015. Nature Photonics, 9, 93.
[Gauthier17] Gauthier, D. et al.: , 2017. Nature Communications, 8.
[Géneaux16] Géneaux, R. et al.: , 2016. Nature Communications, 7, 12583.
[Gruson16] Gruson, V. et al.: , 2016. Science, 354(6313), 734.
[Mairesse03] Mairesse, Y. et al.: , 2003. Science, 302, 1540.
Technics/methods used during the internship:
Ultra short lasers Interferometers Charged particle detectors Vacuum methods Modelling (Python)

Tutor of the internship


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