Over the last decade the processes following excitation of a magnetic recording medium by an optical fs laser pulse have attracted a lot of interest not only from a fundamental physics point of view but also under the aspect of understanding the fundamental limitations of the magnetooptical recording process. Here I will report our studies on Ni films carried out by fs laser spectroscopy and pump probe experiments at the BESSY soft X-ray fs slicing source, providing new insight into the ultrafast electronic and magnetic response stimulated by optical excitation by a fs laser pulse.

Magnetic recording media are comprised of individual nanometer size particles. As these dimensions are reduced in order to increase the storage density, the individual electronic properties, derived from quantum confinement gain in importance. At the extreme limit of mass selected clusters containing less than about 100 atoms not only the ground state properties, but also the dynamic optical response depend uniquely and strongly on the exact size of the particle/cluster.

As an example, we have explored the relaxation processes of electronically excited states in mass selected Au clusters. The phenomena observed depend strongly on the size of the cluster (‘each atom counts’) and range from electron-electron to electron-phonon scattering and from vibrational wavepacket oscillations to a quasi ‘melting’ of the cluster.

Presently this type of spectroscopy is limited by the photon energies available from laboratory laser sources or the low intensity of the slicing source. However the new soft X-ray free electron laser light sources such as FLASH at DESY and the planned BESSY-FEL offer a unique potential to expand these studies in the future.

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