Experimental investigation of the electromagnetic fields at the aperture of a near-field scanning optical microscope

In this work we use an approach that allows a determination of the spatial distribution of the electromagnetic field in the near-field region of the near field scanning optical microscope (NSOM) probe. We studied a MBE grown sample, which contains a 9 nm AlAs layer embedded in a GaAs matrix. The optical contrast arises from the difference in the index of refraction of the two materials. Topography related contrast is avoided by studying a freshly cleaved surface. With the NSOM working in emission mode the reflected light was collected in the far field.