  We use the picosecond acoustic pump-probe technique to study the elastic
properties of monodispersemesoporous silica spheres filled with nickel and
deposited in the form of opal-like films on silica substrates. The picosecond
pump-probe optical transmission signal shows harmonic oscillations
corresponding to the lower energy radial Lamb mode in the vibrational spectrum
of the spheres. These oscillations, with a frequency of several gigahertz last
for several nanoseconds in the spheres with diameter 1050 nm, showing high
homogeneity of the sphere parameters. By analysis of the oscillation spectrum
of films with different sphere diameter and nickel content we obtain the
elastic moduli of the mesoporous silica spheres.
