Near-field Imaging of Optical Resonances in Silicon Metasurfaces Using Photoelectron Microscopy

TL;DR

This paper demonstrates that photoelectron emission microscopy (PEEM) can be used for high-resolution near-field imaging and spectroscopy of optical resonances in silicon metasurfaces, revealing polarization-dependent collective resonances and enabling detailed nanophotonic metrology.

Contribution

The study introduces PEEM as a novel tool for polarization-resolved near-field imaging of silicon metasurfaces, providing insights into collective resonances at the nanoscale.

Findings

PEEM imaging aligns with simulations and reflectance measurements.

Polarization influences the evolution of collective resonances.

Coupling of eight or more resonators leads to collective excitations.

Abstract

Precise control of light-matter interactions at the nanoscale lies at the heart of nanophotonics. Experimental examination at this length scale is challenging, however, since the corresponding electromagnetic near-field is often confined within volumes below the resolution of conventional optical microscopy. In semiconductor nanophotonics electromagnetic fields are further restricted within the confines of individual subwavelength resonators, limiting access to critical light-matter interactions in these structures. In this work, we demonstrate that photoelectron emission microscopy (PEEM) can be used for polarization resolved near-field spectroscopy and imaging of electromagnetic resonances supported by broken-symmetry silicon metasurfaces. We find that the photoemission results, enabled through an in-situ potassium surface layer, are consistent with full-wave simulations and far-field reflectance measurements across visible and near-infrared wavelengths. In addition, we uncover a polarization dependent evolution of collective resonances near the metasurface array edge taking advantage of the far-field excitation and full-field imaging of PEEM. Here, we deduce that coupling between eight resonators or more establishes the collective excitations of this metasurface. All told, we demonstrate that the high-spatial resolution hyperspectral imaging and far-field illumination of PEEM can be leveraged for the metrology of collective, non-local, optical resonances in semiconductor nanophotonic structures.