  Near-field scanning optical microscopy is a powerful technique for imaging
below the diffraction limit, which has been extensively used in bio-medical
imaging and nanophotonics. However, when the electromagnetic fields under
measurement are strongly confined, they can be heavily perturbed by the
presence of the near-field probe itself. Here, taking inspiration from
scattering-cancellation invisibility cloaks, Huygens-Kerker scatterers, and
cloaked sensors, we design and fabricate a cloaked near-field probe. We show
that, by suitably nanostructuring the probe, its electric and magnetic
polarizabilities can be controlled and balanced. As a result, probe-induced
perturbations can be largely suppressed, effectively cloaking the near-field
probe without preventing its ability to measure. We experimentally demonstrate
the cloaking effect by comparing the interaction of conventional and
nanostructured probes with a representative nanophotonic structure, namely, a
1D photonic-crystal cavity. Our results show that, by engineering the structure
of the probe, one can systematically control its back-action on the resonant
fields of the sample and decrease the perturbation by >70% with most of our
modified probes, and by up to one order of magnitude for the best probe, at
probe-sample distances of 100 nm. Our work paves the way for non-invasive
near-field optical microscopy of classical and quantum nano-systems.
