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The availability of ultrashort pulsed laser source technology allows the investigation of dynamics in materials and the study of non equilibrium effects. At the moment, laser sources which provide tens or few hundreds of femotsecond laser pulses are commercially available. This pushes the investigation limit to the sub-ps range and gives access to the so called ultrafast dynamics. Investigation of ultrafast dynamics is applied to ferromagnetic metals in this thesis.

The common configuration to achieve this kind of investigation is the pump and probe technique. A femtosecond pump pulse triggers the dynamics and a femtosecond probe pulse allows to study the induced non-equilibrium effects. When applied to ferromagnetic metals, experimental results raised fundamental questions attracting the attention of the scientific community for over a decade. In 1996 Beaurepaire et al. published a paper [1] which gained the attention of the ultrafast dynamics community. The magnetic material excited with a femtosecond laser source showed a reduction of the magnetization within the first picosecond and a subsequent recovery within a few picoseconds. It was the first time that the magnetic order was manipulated in the sub-ps range, in an all-optical process. How fast can the magnetic order be manipulated? Which processes take place in the femtoseconds dynamics of a ferromagnetic metal? Which dissipation channel of angular momentum can lead to an ultrafast magnetization reduction? There is a fundamental interest in giving answers to these questions, but there are also strong technology interests in the ultrafast manipulation of magnetic order. The first …