Nanoscopy beyond the diffraction limit

In this paper we review the basics of optical investigations with a spatial resolution beyond the diffraction limit. Scanning Near-field Optical Microscopy (SNOM) is shown to be a powerful and sensitive tool, able to transfer a wealth of conventional microscopy methods into the realm of the nanoworld. In particular, integration of SNOM with polarization-modulation methods enables analyzing and measuring optical activity at the nanoscale in solid-state samples. A few examples are presented to elucidate the potential of the technique in analyzing organic nanostructures showing linear and circular dichroism and in unraveling conformational and structural details