  We introduce a wide-field magneto-optical microscope to probe magnetization
dynamics with femtosecond temporal and sub-micrometer spatial resolution. We
carefully calibrate the non-linear dependency between the magnetization of the
sample and the detected light intensity by determining the absolute values of
the magneto-optical polarization rotation. With that, an analytical transfer
function is defined to directly map the recorded intensity to the corresponding
magnetization, which results in significantly reduced acquisition times and
relaxed computational requirements. The performance of the instrument is
characterized by probing the magnetic all-optical switching dynamics of GdFe in
a pump-probe experiment. The high spatial resolution of the microscope allows
for accurately subdividing the laser-excited area into different
fluence-regions in order to capture the strongly non-linear magnetization
dynamics as a function of the optical pump intensity in a single measurement.
