Free Electron-Plasmon Coupling Strength and Near-Field Retrieval through Electron Energy-Dependent Cathodoluminescence Spectroscopy.

Tightly confined optical near fields in plasmonic nanostructures play a pivotal role in important applications ranging from optical sensing to light harvesting. Energetic electrons are ideally suited to probing optical near fields by collecting the resulting cathodoluminescence (CL) light emission. Intriguingly, the CL intensity is determined by the near-field profile along the electron propagation direction, but the retrieval of such field from measurements has remained elusive.

Phase-retrieval Fourier microscopy of partially temporally coherent nanoantenna radiation patterns.

We report an experimental technique for determining phase-resolved radiation patterns of single nanoantennas by phase-retrieval defocused imaging. A key property of nanoantennas is their ability to imprint spatial coherence, for instance, on fluorescent sources. Yet, measuring emitted wavefronts in absence of a reference field is difficult.

Super-Resolution without Imaging: Library-Based Approaches Using Near-to-Far-Field Transduction by a Nanophotonic Structure.

Super-resolution imaging is often viewed in terms of engineering narrow point spread functions, but nanoscale optical metrology can be performed without real-space imaging altogether. In this paper, we investigate how partial knowledge of scattering nanostructures enables extraction of nanoscale spatial information from far-field radiation patterns. We use principal component analysis to find patterns in calibration data and use these patterns to retrieve the position of a point source of light.

Phase-Resolved Surface Plasmon Scattering Probed by Cathodoluminescence Holography.

High-energy (1-100 keV) electrons can coherently couple to plasmonic and dielectric nanostructures, creating cathodoluminescence (CL) of which the spectral features reveal details of the material's resonant modes at a deep-subwavelength spatial resolution. While CL provides fundamental insight in optical modes, detecting its phase has remained elusive. Here, we use Fourier-transform CL holography to determine the far-field phase distribution of fields scattered from plasmonic nanoholes, nanocubes, and helical nanoapertures and reconstruct the angle-resolved phase distributions.

Tunable plasmonic HfN nanoparticles and arrays.

We present the fabrication of tunable plasmonic hafnium nitride (HfN) nanoparticles. HfN is a metallic refractory material with the potential of supporting plasmon resonances in the visible range, similar to silver and gold, but with the additional benefits of high melting point, chemical stability, and mechanical hardness. However, the preparation of HfN nanoparticles and the experimental demonstration of their plasmonic potential are still in their infancy.

Probing the Band Structure of Topological Silicon Photonic Lattices in the Visible Spectrum.

We study two-dimensional hexagonal photonic lattices of silicon Mie resonators with a topological optical band structure in the visible spectral range. We use 30 keV electrons focused to nanoscale spots to map the local optical density of states in topological photonic lattices with deeply subwavelength resolution. By slightly shrinking or expanding the unit cell, we form hexagonal superstructures and observe the opening of a band gap and a splitting of the double-degenerate Dirac cones, which correspond to topologically trivial and nontrivial phases.