Different contrast mechanisms induced by topography artifacts in Near-Field Optical Microscopy

Topography artifacts can affect the elastic scattering optical images in near-field optical microscopy.Moreover, such effects can completely mask the information on the optical properties of the samples, yielding unexpectedly high lateral resolutions. In this letter, we provide experimental evidence of how changes involving the collection geometry and the roughness of the sample can lead to radical modifications of the contrast induced by the artifacts to the optical map. An explanation of the different regimes is provided by means of approach curves in which the optical signal is detected as a function of the probe/sample distance.