  Spin currents can be generated on an ultrafast timescale by excitation of a
ferromagnetic (FM) thin film with a femtosecond laser-pulse. Recently, it has
been demonstrated that these ultrafast spin currents can transport angular
momentum to neighbouring FM layers, being able to change both the magnitude and
orientation of the magnetization in the adjacent layer. In this work, both the
generation and absorption of these optically excited spin currents are
investigated. This is done using non-collinear magnetic bilayers, i.e. two FM
layers separated by a conductive spacer. Spin currents are generated in a Co/Ni
multilayer with out-of-plane (OOP) anisotropy, and absorbed by a Co layer with
an in-plane (IP) anisotropy. This behaviour is confirmed by careful analysis of
the laser-pulse induced magnetization dynamics, whereafter it is demonstrated
that the transverse spin current is absorbed very locally near the injection
interface of the IP layer (90% within the first approx. 2 nm). Moreover, it
will also be shown that this local absorption results in the excitation of THz
standing spin waves within the IP layer. The dispersion measured for these high
frequency spin waves shows a discrepancy with respect to the theoretical
predictions, for which a first explanation involving intermixed interface
regions is proposed. Lastly, the spin current generation is investigated using
different number of repeats for the Co/Ni multilayer, which proves to be of
great relevance for identifying the optical spin current generation mechanism.
