By using a polarization-modulation technique in combination with reflection-mode scanning near-field optical microscopy we are able to determine quantitatively the local polar Kerr rotation on thin magnetic films. As an example, the magneto-optic contrast of magnetic domains thermomagnetically written on a Co/Pt sample is discussed. The size of the magnetic domains is 3×0.5 μm2 and the angular resolution of the local Kerr rotation is better than 0.1°. This measurement technique will make it possible to investigate, e.g., the fine structure of domain walls by scanning near-field optical microscopy.
The implementation of a phase-modulating polarization detector into a scanning near-Ðeld optical microscope allows the imaging of local magneto-optic e †ects with spatial resolution. By taking several pictures at the same location with di †erent detector settings, a quantitative evaluation of magneto-optic e †ects, such as Faraday rotation, becomes possible. Images were taken from thin garnet Ðlms using this method.
We report results obtained with a scanning near-field optical microscope which was developed, recently. The scanning head of the device is mounted on an inverted polarizing microscope. The sample is illuminated through a microfabricated tip which is mounted on a single-mode optical wave-guiding fiber. The light transmitted through the sample is collected in the far field by a microscope lens. The distance between the tip and the sample is controlled by shear force detection, using a nonconventional setup. We applied this new equipment successfully in order to investigate birefringent and dichroic liquid crystal films, using polarization modulation or fluorescence detection, respectively. An optical resolution down to ≈200 nm was obtained on the sample of a cholesteric liquid crystal for a wavelength of 488 nm.
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