A new technique for contrast separation in wide-field magneto-optical Kerr microscopy is introduced. Utilizing the light from eight light emitting diodes, guided to the microscope by glass fibers and being switched synchronously with the camera exposure, domain images with orthogonal in-plane sensitivity can be displayed simultaneously at real-time, and images with pure in-plane or polar contrast can be obtained. The benefit of this new method of contrast separation is demonstrated for Permalloy films, a NdFeB sinter magnet, and a cobalt crystal. Moreover, the new technique is shown to strongly enhance the sensitivity of Kerr microscopy by eliminating parasitic contrast contributions occurring in conventional setups. A doubling of the in-plane domain contrast and a sensitivity to Kerr rotations as low as 0.6 mdeg is demonstrated.
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Exceptions do occur if the magnetization is tilted out-of-plane by only some degrees and if the angle of incidence is large, i.e., by using objective lenses with high numerical aperture. See Ref. 29 for details.
The term “real-time” refers to the observation of dynamic magnetization processes as fast as the eye can follow without visually noticing a delay or inertia in the domain motion. The latter would occur if the frame rate would only be some Hertz or if frames are averaged to suppress noise in the images.
The factor 2 is due to the geometry of the experiment: the contrast is generated by two oppositely saturated states, which have positive and negative Kerr rotation angles, respectively.
