  Ultrafast two-color pump-probe measurements, involving coherent acoustic
phonon (CAP) waves, have provided information simultaneously on the mechanical
properties and on the electronic structure of ferromagnetic GaMnAs. The elastic
constant C11 of Ga1-xMnxAs (0.03<x<0.07) are observed to be systematically
smaller than those of GaAs. Both C11 and Vs of GaMnAs are found to increase
with temperature (78 K<T<295 K), again in contrast to the opposite behavior in
GaAs. In addition, the fundamental bandgap (at E0 critical point) of Ga1-xMnxAs
is found to shift slightly to higher energies with Mn concentration.
