Quasinormal mode theory and modelling of electron energy loss spectroscopy for plasmonic nanostructures

Abstract

Understanding light-matter interactions using localized surface plasmons (LSPs) is of fundamental interest in classical and quantum plasmonics and has a wide range of applications. In order to understand the spatial properties of LSPs, electron energy loss spectroscopy (EELS) is a common and powerful method of spatially resolving the extreme localized fields that can be obtained with metal resonators. However, modelling EELS for general shaped resonators presents a major challenge in computational electrodynamics, requiring the full photon Green function as a function of two space points and frequency. Here we present an intuitive and computationally simple method for computing EELS maps of plasmonic resonators using a quasinormal mode (QNM) expansion technique. By separating the contribution of the QNM and the bulk material, we give closed-form analytical formulas for the plasmonic QNM contribution to the EELS maps. We exemplify our technique for a split ring resonator, a gold nanorod, and a nanorod dimer structure. The method is accurate, intuitive, and gives orders of magnitude improvements over direct dipole simulations that numerically solve the full 3D Maxwell equations. We also show how the same QNM Green function can be used to obtain the Purcell factor (and projected local density of optical states) from quantum dipole emitters or two level atoms, and we demonstrate how the spectral features differ in general to the EELS spectrum.

9 pages, 4 figures

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Cited by in corpus (7)

• Light interaction with photonic and plasmonic resonances
• Nonlocal quasinormal modes for arbitrarily shaped three-dimensional plasmonic resonators
• Regularized quasinormal modes for plasmonic resonators and open cavities
• Momentum-resolved Electron Energy Loss Spectroscopy for Mapping the Photonic Density of States
• Dissipative modes, Purcell factors and directional beta factors in gold bowtie nanoantenna structures
• An efficient solver for the generalized normal modes of non-uniform open optical resonators
• Resonant states of structured photonic time crystals