Electron, light, and matter interactions beyond nonrecoil approximations

Abstract

This thesis investigates quantum-coherent interactions between slow electrons and optical fields beyond the conventional nonrecoil approximation. While high-energy electron–photon interactions are well described within this approximation, slow electrons experience significant momentum exchange and recoil when interacting with intense near-fields. The first part focuses on spontaneous light emission studied through cathodoluminescence spectroscopy. In WSe2, combined experiments and simulations reveal that thin flakes exhibit strong coupling between Cherenkov radiation and the A-exciton, whereas in thicker samples, deceleration-induced emission becomes dominant. Furthermore, in GaN/AlGaN heterostructures, the excitation of secondary electrons leads to depth-dependent luminescence, enabling selective probing of defect and interface states. The second part of this thesis explores stimulated interactions using a Maxwell–Schrödinger framework to simulate the dynamics of slow-electron wavepackets near laser-excited gold nanorods. By tuning the laser polarization, near-field geometry, and excitation configuration, both amplitude and phase modulation of the electron wavefunction are achieved, extending beyond the conventional PINEM description. Furthermore, rotating plasmonic fields generated by two counterpropagating laser pulses with a controlled temporal delay are shown to transfer angular momentum, direction-dependent recoil, and energy exchange within the electron wavepacket, introducing the concept of plasmonic rotors for coherent electron control. Finally, custom-designed components a diverging electrostatic lens and a gridless retarding field energy analyzer are developed for integration into SEM. This work establishes slow electrons as powerful quantum probes for nanophotonics, ultrafast spectroscopy, and quantum information science