Ultrashort laser pulses enable the observation as well as the control of physical processes within atoms and clusters. The focus of this thesis lies on electronic processes in a helium nanoplasma. The temporal development of a transient nanoplasma is studied using pump-probe experiments up to a nanosecond timescale. Thus, the distribution of strongly bound quasi-free electrons in the plasma potential is mapped and the disintegration of the plasma by electron recombination into Rydberg states is demonstrated.<eng>
