  The remagnetization process after ultrafast demagnetization can be described
by relaxation mechanisms between the spin, electron, and lattice reservoirs.
Thereby, collective spin excitations in form of spin waves and their angular
momentum transfer play an important role on the longer timescales. In this
work, we address the question whether the strength of demagnetization affects
the coherency and the phase of the excited spin waves. We present a study of
coherent magnetization dynamics in thin nickel films after ultrafast
demagnetization using the all-optical, time-resolved magneto-optical
Kerr-effect (tr-MOKE) technique. The largest coherent oscillation amplitude was
observed for strongly quenched systems, showing the conservation of coherency
for demagnetizations of up to 90%. Moreover, the phase of the excited
spin-waves increases with pump power, indicating a delayed start of the
precession during the remagnetization.
