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Alok Kumar Pandey "Faisceaux vortex et vector-vortex de très haute charge par génération d'harmoniques : génération, caractérisation et amplification dans un plasma de laser X"

200/0-Auditorium - Auditorium P. Lehmann (IJCLab)

200/0-Auditorium - Auditorium P. Lehmann


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"Twisted high order harmonics: generation, characterization and amplification in XRL plasma."

Abstract :

This manuscript presents the thesis work done by Alok Kumar Pandey on the LASERIX multibeam platform of the Paris-Saclay University on the Orsay campus. A complete study of the characterization of vortex beams of intense femtosecond light has been performed. These beams are produced by inserting a spiral phase plate in the path of the infrared beam and are characterized by a Shack Hartmann wavefront sensor. This method of characterization in phase and in the amplitude of the electric field of the laser allows a precise and quantitative modal decomposition of the beam in the base of the Laguerre Gauss modes. The plates used allow to induce an angular momentum of the light of integer values 1 to 4, in positive or negative according to the direction of variation of the phase. These beams were then used to generate high-order harmonics in a rare gas cell. The extreme ultraviolet beams thus produced were characterized by a EUV Hartmann wavefront sensor. Orbital moments as high as l=100 can be produced and completely characterized from the initial 25th harmonic of the infrared beam, thus verifying the law that the orbital angular momentum of the harmonic vortex beam is equal to the product of the infrared beam moment and the harmonic order. A more complex state of light has also been studied: vortex vector beams for which not only the spatial phase of the beam verifies an azimuthal dependence but also the polarization varies spatially. It can be radial or azimuthal. The characterization of harmonic beams produced by infrared vortex vector beams allows demonstrating that we obtain vortex vector beams in the extreme ultraviolet and that they are able to propagate. The structure of these beams has been completely described by numerical simulations validated by experimental results. Finally, the last chapter presents the results of the amplification of an extreme ultraviolet harmonic vortex beam carrying orbital angular momentum in a transient collisional X-ray laser plasma. Fine effects of the orbital angular momentum on the beam propagation in the amplifying medium have been demonstrated and analyzed, in comparison with numerical codes. The present work demonstrates that X-ray laser plasmas allow harmonic beam amplification capable of preserving all its spatial properties, in particular the orbital angular momentum.



Organized by

Membres du jury :
Direction de thèse: Mme Sophie KAZAMIAS - Professeur des universités - Université Paris-Saclay GS Physique
Co-encadrant de thèse: M. Olivier GUILBAUD - Maître de conférences - Université Paris-Saclay GS Physique
Rapporteur: M. Eric CONSTANT - Directeur de recherche - Institut Lumière Matière (ILM)
Rapporteur: M. Eric MEVEL - Professeur des universités - Université de Bordeaux
Examinateur: M. Shambhu GHIMIRE - Directeur de recherche - PULSE Institute at Stanford University
Examinateur: Mme Nirit DUDOVICH - Professeur - Weizmann Institute
Examinateur: M. Jacques ROBERT - Professeur des universités - Université Paris-Saclay GS Physique