  Time-resolved transmittance measurements performed on
Ga$_{0.94}$Mn$_{0.06}$As in the vicinity of the Mn-induced mid-infrared
absorption band are presented. Upon photo-excitation, a slow increase (hundreds
of ps timescale) of the differential transmittance is observed and found to be
directly related to demagnetization. The temporal profiles of the transmittance
and of the demagnetization measured by time-resolved magneto-optical Kerr
spectroscopy are found to coincide. Well below the Curie temperature, the
maximum amplitude of the slow component of the differential transmittance as a
function of the probe energy is on the rising edge of the linear absorption
peak, suggesting that ferromagnetic ordering can be explained by a coupling of
the Mn local spins through bound magnetic polarons.
