Near-field hyper-spectral imaging of resonant Mie modes in a dielectric island

All-dielectric sub-micrometric particles have been successfully exploited for light management in a plethora of applications at visible and near-infrared frequencies. However, the investigation of the intricacies of the Mie resonances at the sub-wavelength scale has been hampered by the limitations of conventional near-field methods. In this paper, we address the spatial and spectral mapping of multipolar modes of a Si island by hyper-spectral imaging. The simultaneous detection of several resonant modes allows us to clarify the role of the substrate and the incidence angle of the impinging light, highlighting spectral splitting of the quadrupolar mode and resulting in different spatial features of the field intensity. We explore theoretically and experimentally such spatial features. Details as small as 200 nm can be detected and agree with simulations based on the finite difference time domain method. Our results are relevant to near-field imaging of dielectric structures, the comprehension of the resonant features of sub-micrometric Mie antennas, beam steering, and the resonant coupling with light emitters. Our analysis suggests a novel approach to control the absorption of a single emitter in the framework of surface enhanced absorption or stimulated emission applications.