Nowadays, it is well established that the superposition of higher-order harmonics (HOH), resulting from the non-linear response of matter to intense laser pulses (greater than 1013 W/cm2), comprises an avenue towards ultra-short pulse generation reaching the attosecond time-scale. Although this field has progressed significantly there are still a number of difficulties one has to surmount. An arbitrary superposition of harmonics may not depict close temporal confinement. Thus, it is of great importance to know the temporal characteristics of the superposition. Towards this goal an experimental method has been previously proposed the measurement of the relative phase distribution of the spectral components of a superposition of higherorder harmonics or the phase distribution of individual ones. This method is based on the phase-control principles of the excitation probability of an excited atom by the harmonic radiation and its fundamental frequency. The work of this thesis is focused on implementing this proposed method in order to directly measure the phase distributions of a short pulse produced by the superposition of the third and fifth harmonics of a Ti:Sapphire laser system generated in Xe gas. For In this measurement we used a previously proposed dispersionless experimental set-up based on a transmission grating interferometer. From the retrieved phase and the measured spectral amplitude distributions the temporal profile of the pulses could be reconstructed and was found in good agreement with the simulated one. This work opens-up a new route for the characterization of harmonics, for the temporal characterization of XUV pulses of ultra-short duration.
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