Abstract
Optically resonant nanoantennae are key building blocks for metasurfaces, nanosensors, and nanophotonic light sources due to their ability to control the amplitude, phase, directivity, and polarization of scattered light. Here, we report an experimental technique for the full recovery of all degrees of freedom encoded in the far-field radiated by a single nanostructure using a high-NA Fourier microscope equipped with digital off-axis holography. This method enables full decomposition of antenna-physics in its multipole contributions and gives full access to the orbital and spin angular momentum properties of light scattered by single nano-objects. Our results demonstrate these capabilities through a quantitative assessment of the purity of the “selection rules” for orbital angular momentum transfer by plasmonic spiral nanostructures.
Highlights
A cornerstone of nanophotonics is to precisely control the resonances of individual metallic and dielectric scatterers that form elementary building blocks of nanophotonic devices such as metasurfaces and nanoantennae
Experimental set-up Our novel experimental technique for angle-resolved amplitude, polarization, and phase imaging of single nano-objects is based on a combination of Fourier microscopy, polarimetry, and digital holography
Digital holographic microscopy was recently applied to nanophotonic structures[33,34,35,36], these studies were mostly aimed at real space, i.e., sample plane, imaging
Summary
A cornerstone of nanophotonics is to precisely control the resonances of individual metallic and dielectric scatterers that form elementary building blocks of nanophotonic devices such as metasurfaces and nanoantennae. The underlying physics is based on the fact that subwavelength geometric tailoring controls the near-field multipolar resonances of nanoscatterers, which in turn allows for a precise manipulation of the amplitude, phase, and polarization of light scattered into the far field. Metasurfaces based on metallic and dielectric nanoresonators provide near-arbitrary control over the phase, Even though a successful design requires a precise understanding of the type of multipolar resonances supported by a nano-object, the complex superposition one can excite, and how these radiate into the far field, such an understanding commonly relies largely on numerical results and is supported only indirectly by experimental evidence. A measurement of the full polarization, amplitude, and phase of light for each angle in the 4π far-field radiation pattern of a nanoantenna enables full decomposition of the antenna’s response in its locally induced multipoles (see Fig. 1). We demonstrate the potential of this method by phase resolving the radiation pattern of single spiral-shaped nanoscatterers that generate orbital angular momentum (OAM)[18]
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