Magnetic domain imaging with a scanning near-field optical microscope using a modified Sagnac interferometer

We report on the combination of a scanning near-field optical microscope an d a modified Sagnac interferometer for magnetic-domain imaging in the refle ction mode. The Sagnac interferometer is used for detection of the magnetoo ptical Kerr effect, Since the interferometer is inherently insensitive to p olarization changes caused by topography effects, magnetic-domain imaging i s not limited to samples with flat surfaces. In this way, it is possible to image magnetic bits written on the tracks of a magneto-optical disc. that has a rather pronounced surface profile.