AFM topographical image of a particular metallic nano-structure produced by e-beam lithography on an SiOx substrate. Baselength of letter "K" = 310 nm.	Composite image of the same structure as on the left: AFM (height) and aSNOM signal (color) for s-polarized excitation of 833 nm incident in direction of view.

The critical task for any nano-optical work is the collection and discrimination of light emitted from a volume of matter only a few nm in size. In spectro-microscopy, the resolution is typically limited to some fraction of the wavelength. From the variety of possible nano-optical microscopy techniques we employ the (arguably) most promising for ultimate lateral resolution at surfaces and interfaces: In contrast to scanning nearfield optical microscopy (SNOM), apertureless SNOM (aSNOM) is based upon localized field enhancement at the apex of an extremely sharp needle.

In our home-built aSNOM we use off-the-shelf AFM Si tips that have an effective apex radius of well below 10 nm, which represents well the lateral resolutions we achieve routinely - demonstrated for example with SERS hotspots. To further convince ourselves of the proper interpretation of recorded signal, we have undertaken a series of of full 3-dimensional simulations of the entire imaging process as the probing tip scans over metallic inclusions in a dielectric matrix.

cross-polarization