Link between Cathodoluminescence and Electron Energy Loss Spectroscopy and the Radiative and Full Electromagnetic Local Density of States

Abstract

Electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have proved during the past few years to be tremendous tools to study surface plasmons in metallic nanoparticles, thanks to an extremely high spatial resolution combined with a broad spectral range. Despite their apparent close resemblance, qualitative differences between EELS and CL have been theoretically as well as experimentally pinpointed. We demonstrate that these differences are recovered when comparing the full electromagnetic local density of states (EMLDOS) and the radiative EMLDOS. Following the known relation established between EELS and the projection along the electron trajectory of the full EMLDOS, we introduce a formalism based on the Maxwell electric Green tensor to draw a link between CL and the projection along the electron trajectory of the radiative EMLDOS. We discuss in simple terms the differences between EELS (projected full EMLDOS) and CL (projected radiative EMLDOS) through modal decompositions obtained in the quasistatic approximation. Contrary to EELS, CL probes only the radiative modes. Furthermore, CL resonant line shapes may be shifted and asymmetric compared to EELS. The CL asymmetry is due to interferences in the far-field radiation from spectrally and spatially overlapping modes. Our analytical expressions are illustrated through boundary element method numerical simulations.

Low‐Loss Hybrid High‐Index Dielectric Particles on a Mirror for Extreme Light Confinement

“…The sample was imaged by exciting the nanoparticle with energetic electrons (30 kV) in an SEM and collecting the radiation emitted as a function of the electron beam position. The spatially integrated CL emission across the PoM is shown in Figure c and closely resembles the measured dark‐field scattering spectra (see Figure S8 in the Supporting Information for additional CL data) . The CL map spectrally averaged ± 10 nm around the resonant wavelength is shown in Figure d.…”

“…The spatially integrated CL emission across the PoM is shown in Figure 4c and closely resembles the measured dark-field scattering spectra (see Figure S8 in the Supporting Information for additional CL data). [50,51] The CL map spectrally averaged ± 10 nm around the resonant wavelength is shown in Figure 4d. The signal originates mostly at the edge of the nanoparticle, i.e., precisely in the region with the largest Purcell enhancement.…”

Large near-to-far field spectral shifts for terahertz resonances

“…The absorption spectrum peaks at the natural frequency of 0.68 THz, whereas the peak of the scattering spectrum is around 0.75 THz. These kinds of shifts between scattering and absorption spectrum have been experimentally as well as theoretically reported in several papers [37][38][39]. The use of a good conductor at THz frequencies is manifested by the fact that the spectral absorption is far less than the scattering.…”

Quantum theory of near-field optical imaging with rare-earth atomic clusters

“…Under these specific detection conditions, it was theoretically demonstrated that the signals delivered in this configuration of scanning near field optical microscope (SNOM) are proportional to the electric part of the photonic LDOS at the scanned positions of the point-like light source [9]. Note that we are leaving aside here electron microscopy tools like electron energy loss spectroscopy (EELS) which are also capable to access the photonic LDOS on a subwavelength spatial resolution [10][11][12].…”