Cathodoluminescence Wavefront Retrieval

Free-electron-based nanoscopy enables the study of optical excitations in materials with deep-subwavelength spatial resolution, with cathodoluminescence (CL) being one of the most useful signals. When combined with an optical collection system, CL measurements can access multidimensional information on light; yet the phase of the emitted optical fields has remained largely elusive. Here, we demonstrate a reference-free phase retrieval approach for far-field CL wavefronts using the Gerchberg-Saxton algorithm implemented with real-space and angular-space CL intensity data. Applying this approach to representative nanostructures, including a planar surface, nanosphere, plasmonic crystal, and nanowire, we reconstructed distinct phase distributions that revealed their underlying radiation mechanisms. This reference-free framework offers a robust and flexible route for retrieving the phase of electron beam-excited optical fields without relying on a reference wave, making it readily extendable to a wide range of nanostructures.