Génération d'impulsions attosecondes sur miroir plasma relativiste

Abstract : When an ultra intense femtosecond laser ($I>10^{16}W.cm^{-2}$) with high contrast is focused on a solid target, the laser field at focus is high enough to completely ionize the target surface during the rising edge of the laser pulse and form a plasma. This plasma is so dense (the electron density is of the order of hundred times the critical density) that it completely reflects the incident laser beam in the specular direction: this is the so-called " plasma mirror ". When laser intensity becomes very high, the non-linear response of the plasma mirror to the laser field periodically deforms the incident electric field leading to high harmonic generation in the reflected beam. In the temporal domain this harmonic spectrum is associated to a train of attosecond pulses. The goals of my PhD were to get a better comprehension of the properties of harmonic beams produced on plasma mirrors and design new methods to control theses properties, notably in order to produce isolated attosecond pulses instead of trains. Initially, we imagined and modeled the first realistic technique to generate isolated attosecond on plasma mirrors. This brand new approach is based on a totally new physical effect: "the attosecond lighthouse effect". Its principle consists in sending the attosecond pulses of the train in different directions and selects one of these pulses by putting a slit in the far field. Despites its simplicity, this technique is very general and applies to any high harmonic generation mechanisms. Moreover, the attosecond lighthouse effect has many other applications (e.g in metrology). In particular, it paves the way to attosecond pump-probe experiments. Then, we studied the spatial properties of these harmonics, whose control and characterization are crucial if one wants to use this source in future application experiments. For instance, we need to control very precisely the harmonic beam divergence in order to achieve the attosecond lighthouse effect and get isolated attosecond pulses. At very high intensities, the plasma mirror dents and gets curved by the inhomogeneous radiation pressure of the laser field at focus. The plasma mirror surface thus acts as a curved surface, which focuses the harmonic beam in front of the target and fixes its spatial properties. We developed a fully analytical and predictive model for the surface deformation, thanks to which we are now able to calculate very easily the spatial properties of the generated harmonic beams. we validated this model through hundreds of 1D and 2D PIC simulations.
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Henri Paul Vincenti. Génération d'impulsions attosecondes sur miroir plasma relativiste. Physique des plasmas [physics.plasm-ph]. Ecole Polytechnique X, 2012. Français. ⟨pastel-00787281⟩

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