  Magnetic and spintronic media have offered fundamental scientific subjects
and technological applications. Magneto-optic Kerr effect (MOKE) microscopy
provides the most accessible platform to study the dynamics of spins, magnetic
quasi-particles, and domain walls. However, in the research of nanoscale spin
textures and state-of-the-art spintronic devices, optical techniques are
generally restricted by the extremely weak magneto-optical activity and
diffraction limit. Highly sophisticated, expensive electron microscopy and
scanning probe methods thus have come to the forefront. Here, we show that
perfect optical absorption (POA) dramatically improves the performance and
functionality of MOKE microscopy. For 1-nm-thin Co film, we demonstrate a Kerr
amplitude as large as 20 degree and magnetic domain imaging visibility of 0.47.
Especially, POA-enhanced MOKE microscopy enables real-time detection and
statistical analysis of sub-wavelength magnetic domain reversals. Furthermore,
we exploit enhanced magneto-optic birefringence and demonstrate analyser-free
MOKE microscopy. The POA technique is promising for optical investigations and
applications of nanomagnetic systems.
