Post compression d'impulsions intenses ultra-brèves et mise en forme spatiale pour la génération d'impulsions attosecondes intenses

Antoine Dubrouil 1
1 groupe harmonique
CELIA - Centre d'Etudes Lasers Intenses et Applications
Abstract : The generation of high order harmonics in a gaseous medium is a phenomenon described by a three steps model : subjected to a strong laser eld irradiation, an atom (or molecule) can undergo a tunneling ionization. The ejected electron is accelerated in the laser eld and recombine on its parent ion leading to the emission of an XUV photon. The XUV radiation can be emitted in the form of attosecond pulses (1 as = 10^-18 s), and it is then an ideal tool to probe the electronic structure of atoms or molecules which require the highest time resolution. However, the intensity of this radiation is usually not su cient to induce non-linear processes (two-photon transitions).In the frame of this work, we have developed a harmonic source capable of producing an intense XUV radiation which allows access to the non-linear physics in this wavelength domain. To achieve these results, signi cant work on the infrared generating pulses was necessary, both in the spatial and temporal domain. We have developed a technique for spatial shaping of intense laser beams, and a post compression technique tted to high energy pulses. This thesis is therefore divided into three stages : - The development of an high energy harmonic source and related diagnostics. We use a Ti : sapphire laser system for this source which delivers 40-fs pulses up to an energy of 150 mJ at 10 Hz repetition rate. Good optimization conditions were obtained, leading to energies of the order of J in the case of generation in argon. - The development of a spatial shaping technique adapted to intense laser beams and to harmonic generation. The device is based on re ection optics, and the interferences of two beams. It can produce in the focal region beams with a constant intensity over a large volume ( at top beams) and thus provide additional control of the harmonics generating process. - The development of a post compression technique in guided geometry based on the ionization induced spectral broadening. This technique is suitable for intense pulses (3.5 TW) and produces pulses above the terawatt level in the 10-fs range. This technique therefore provides a unique source for harmonic generation. These two approaches have been tested and validated for high order harmonics generation, and the results open interesting perspectives such as the generation of isolated attosecond pulses of high energy (> 100 nJ).
Document type :
Theses
High Energy Physics - Experiment. Université Sciences et Technologies - Bordeaux I, 2011. French


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Antoine Dubrouil. Post compression d'impulsions intenses ultra-brèves et mise en forme spatiale pour la génération d'impulsions attosecondes intenses. High Energy Physics - Experiment. Université Sciences et Technologies - Bordeaux I, 2011. French. <tel-00669335>

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