  We present a study of photo-excited magnetization dynamics in ferromagnetic
(Ga,Mn)As films observed by time-resolved magneto-optical measurements. The
magnetization precession triggered by linearly polarized optical pulses in the
absence of an external field shows a strong dependence on photon frequency when
the photo-excitation energy approaches the band-edge of (Ga,Mn)As. This can be
understood in terms of magnetic anisotropy modulation by both laser heating of
the sample and by hole-induced non-thermal paths. Our findings provide a means
for identifying the transition of laser-triggered magnetization dynamics from
thermal to non-thermal mechanisms, a result that is of importance for ultrafast
optical spin manipulation in ferromagnetic materials via non-thermal paths.
