“…By precharacterizing the tips in far-field experiments and using different experimental configurations, we succeeded to selectively map different components of the plasmonic near-fields. Numerous experimental and theoretical studies have been aimed at elucidating the orientation of the electromagnetic field components in the near-field of an aperture SNOM tip and their role in image formation. − In contrast to radiative fields in homogeneous media that can be described in terms of transverse waves, the electromagnetic near-fields around subwavelength structures (including the aperture of a SNOM tip) are fully vectorial in nature, so that the notion of polarization is generally not applicable in the near-field regime. − However, typical aperture SNOM tips with circular, subwavelength apertures have been shown to probe only the vector components of the electromagnetic field that are transverse to the tip axis, that is, parallel to the aperture plane. In contrast, bare fiber tips, scattering tips, ,, split-ring type aperture tips, , and tips with apertures approximately a full wavelength in diameter can probe longitudinal field components as well.…”