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Electron-Driven Photon Sources for Spectral Interferometry using Electron Microscopes

Photon induced near-field electron microscopy has been recently introduced to investigate the dynamics of near-field distributions in nanostructures, with femtosecond time and angstrom spatial resolution [1]. In this technique a laser beam excites both a photoemission electron gun and the sample inside an electron microscope chamber. The electron beams then probe the laser-induced excitations. Achieving attosecond temporal resolution to probe electron dynamics is however challenging, due to the requirement for a perfect synchronization between the electron waves and laser light. Recently an alternative approach based on cathodoluminescence (CL) has been proposed [2]. In this way, the interaction of swift electrons with a precisely designed electron-driven photon source (EDPHS) causes radiation of ultrashort optical pulses, which are focused onto the sample (Fig. 1a). The sample interacts with both the EDPHS radiation and the electron. The overall CL emission is controlled by the distance between the sample and the EDPHS. The distance-energy correlation map between the CL radiations from both the sample and EDPHS is then recorded and used to recover the spectral phase and time-resolved responses of the sample [3, 4] (Fig. 1b).