Time gated high order harmonic generation

High Order Harmonic Generation (HHG) is a coherent XUV source obtained by focusing an intense laser pulse into a gas medium. After spectral filtering, HHG can be considered in the time domain as a source of a train of attosecond pulses which are spaced by half an optical period of the laser field. This characteristic has attracted a lots of interest since it opens the way to attosecond physics. Generating a single attosecond pulse is one of the main challenge. According to simulations, one of the solutions to achieve this goal is to confine the harmonic generation inside a temporal window smaller than one optical cycle of the fundamental laser. In this manuscript, we present a method which allows us to confine the harmonic emission inside a given temporal window and can allow to generate isolated attosecond pulses. This approach relies on the extreme sensitivity of high order harmonic generation on the ellipticity of the fundamental laser field. We developed and analysed a method to modulate temporally the ellipticity of the laser field. To observe the confinement on HHG, we studied, in the first step, the spectral modifications induced by the polarization modulation. In a second step, we performed direct temporal measurements of high order harmonics pulses generated by laser pulses with a time varying polarization. A clear confinement of high harmonic emission is observed. This work also shows that using polarization modulated 10 fs pulses results in the production of an isolated attosecond pulse. To approach this goal, we also developed a new extra-cavity pulse-compression technique suitable for generating high-energy sub-10 femtosecond pulses. (author)