Optical resonances in silica-nanosphere dimers and trimers probed with high-energy electrons at the nanoscale

TL;DR

This study uses electron-beam spectroscopy in a high-energy electron microscope to investigate optical resonances in silica nanosphere dimers and trimers, revealing mode coupling effects and local photonic density of states at the nanoscale.

Contribution

It introduces a novel application of electron-beam spectroscopy to probe optical modes in nanoscale photonic molecules, demonstrating detailed spectral features and mode interactions.

Findings

Identification of whispering gallery modes in silica monomers

Observation of energy shifts and peak broadening in dimers and trimers due to coupling

Demonstration of local photonic density of states extraction at nanometer resolution

Abstract

Optical dielectric resonances have the ability to modulate optical energy, and by coupling multiple resonators into photonic molecules, new opportunities emerge in spectral engineering. Using electron-beam spectroscopy, in a 300-keV scanning transmission electron microscope, we probe optical modes of photonic molecules at the nanometer scale. Monochromated electron energy-loss spectra of 400nm-silica-sphere monomers, dimers and trimers display series of sharp peaks in the ultraviolet region. For monomers, the peaks are assigned to low angular number optical whispering gallery modes. For dimers and trimers, experimental observations, supported by simulations, reveal energy shifts and peak broadening resulting from coupling between spherical modes. Variations in spectra for different electron probe positions demonstrate the possibility to extract information on local photonic density of states at the nanometer scale.