Abstract |
Nowadays, it is well established that the superposition of higher-order harmonics (HOH), as a result of the non-linear response of matter to intense laser pulses (greater than 1013 W/cm2), comprises an avenue towards ultra-short pulses in the attosecond time-scale. Although this approach has significant advantages there are still a number of difficulties one has to surmount. A blind superposition of harmonics will result on loss of all short-time-structure of the field. Thus, it is of great importance to know their temporal characteristics. In this framework an experimental method has been proposed for the measurement of the relative phase distribution of the spectral components of a superposition of higher-order harmonics or the phase distribution of individual ones. This method is based on the phase-control of the excitation probability between the harmonic radiation and its fundamental source. The work of this Thesis is focused in implementing, for the first time, this proposed method to directly measure the phase distribution of a short third harmonic pulse generated by a Ti:Sapphire laser system. In implementing this we used a proposed experimental set-up based on a transmission grating interferometer having the advantage to be dispersionless. From the retrieved phase and the measured spectral amplitude distribution the temporal profile of the measured third harmonic pulse could be reconstructed. This work opens-up a new route to characterize harmonics, which can be extended to the temporal characterization of XUV pulses of ultra-short pulse duration.
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