  In the framework of magnonics all-optical femtosecond laser experiments are
used to study spin waves and their relaxation paths. Magnonic crystal
structures based on antidots allow the control over the spin-wave modes. In
these two-dimensional magnetic metamaterials with periodicities in the
wave-length range of dipolar spin waves the spin-wave bands and dispersion are
modified. Hence, a specific selection of spin-wave modes excited by laser
pulses is possible. Different to photonics, the modes depend strongly on the
strength of the magneto-static potential at around each antidot site - the
dipolar field. While this may lead to a mode localization, also for filling
fractions around or below 10%, Bloch states are found in low damping
ferromagnetic metals. In this chapter, an overview of these mechanisms is given
and the connection to spin-wave band spectra calculated from an analytical
model is established. Namely, the plane-wave method yields flattened bands as
well as band gaps at the antidot lattice Brillouin zone boundary.
