The specificities and advantages of magneto-optics (MO) for studying the ma
gnetism of thin film structures: sensitivity, high space and time resolutio
n, and wavelength discrimination, are ri viewed. Based on MO imaging experi
ments, two fundamental studies on the dynamics of the magnetization reversa
l in an ultrathin cobalt magnetic layer with perpendicular anisotropy and r
elated dot arrays, or of the thermomagnetic MO recording-writing process, a
re presented.