Cathodoluminescence Enhancement Mechanisms in Silica Microspheres

TL;DR

This study analyzes the mechanisms of cathodoluminescence in silica microspheres, revealing surface photon generation, high-NA collimation, and potential for advanced quantum measurement applications.

Contribution

It decomposes CL mechanisms in silica spheres, demonstrating surface photon generation and high-quality collimation, enabling new quantum measurement techniques.

Findings

Photon generation occurs on the sphere's surface.

Spheres act as high-NA collimating lenses for CL.

Enhanced mode quality for free-space CL.

Abstract

Cathodoluminescence (CL) enables optical-frequency analysis of samples with nanometer resolutions, originating from the interaction of a focused electron beam with radiative electronic states, or directly with the optical modes of the sample. Here we decompose the various mechanisms underlying CL generation and emission from an archetype spherical resonator using its spectral, angular and spatially resolved features. We investigate radiation of optical whispering-gallery modes in regimes of coherent and incoherent luminescence. The use of different experimental regimes allows us to disentangle the different contributions to the CL in spheres, namely, photon absorption, generation and radiative leakage, and conclude that the photon generation occurs precisely on the sphere's surface. In addition, the spheres serve as high-NA collimating lenses for CL, resulting in mode quality unprecedented for CL in free space. We believe that such collimated and directed CL in free space will enhance existing quantum measurements of CL and facilitate new ones, such as high-rate electron-photon entangled pairs, CL from quantum emitters, and homodyne analysis of CL.