Abstract : The work in this thesis aimed to study a geometry of XUV lasers inspired by high power laser. This architecture, consisting of an injector (a source of high-order harmonics) coupled to an amplifier (plasma created by laser), corresponds to that of a laser chain in the spectral range of the XUV. The laser at 32.8 nm studied here, is produced by the injection of high-order harmonic in a krypton plasma created by Optical Field Ionization (OFI). This scheme, initially tested by T. Ditmire in 1995, was validated in 2003 with a plasma amplifier created by the interaction of intense laser and a gaseous medium at the Laboratoire d'Optique Appliquée. This thesis is a continuation of that work in trying to address different aspects, not only a better understanding the physical processes involved, but also the spatio-temporal characterization of this type of source. We have demonstrated experimentally for the first time a source in the XUV, witch can be both highly compact, energetic (1 μJ per pulse), close to the diffraction limit and Fourier transform limited. Indeed, through the spatial filtering of harmonics by the amplifying medium, the injected XUV laser at 32.8 nm shows a Gaussian spatial profile with a divergence of 0.7 mrad (at 1/e2). The wavefront was measured with a Hartmann sensor and presents a value of λ/17 in standard deviation, demonstrating that the XUV source is diffraction limited. The temporal characterization of laser shows that the coherence time is of the order of the duration of spontaneous emission of the amplifier. The temporal coherence presents a Gaussian profile with a relative spectral width Δλ/λ equal to 10-5 (FWHM) corresponding to a pulse duration of about 5 ps.