Fatemeh Chahshouri

Free-electron interactions with light and matter have long served as a cornerstone for exploring the quantum and ultrafast dynamics of material excitation. In recent years, this paradigm has evolved from a classical description of radiation and acceleration toward a fully quantum framework, transforming our understanding of light-matter interactions at the single-electron level. These advances have opened new opportunities in high-resolution imaging, ultrafast spectroscopy, interferometry, and the coherent shaping of electron wavepackets. This review surveys stimulated interactions between slow electrons and light, encompassing free-space and near-field mediated mechanisms. We discuss how free-space optical fields coherently modulate electron momentum and energy, and how near-field coupling in nanophotonic and plasmonic structures enables strong, phase-matched, efficient momentum exchange with the electron wavepacket. We further describe electron recoil, which is significant in the slow-electron regime, and temporal and spatial wavepacket shaping that enhances coupling efficiency and extends access to quantum-coherent regimes. Building on these foundations, we outline emerging frameworks including hybrid optical-electrostatic modulation, ponderomotive laser-based aberration correction, and optical electron interferometry. By unifying these developments, stimulated electron-light interactions provide a versatile route to precise beam control, quantum-state engineering, and tailored light-matter coupling, with implications for ultrafast spectroscopy, nanoscale metrology, attosecond pulse generation, electron-photon entanglement, and the creation of nonclassical states of light.

The interaction between free electrons and laser‐induced near‐fields provides a platform to study ultrafast processes and quantum phenomena while enabling precise manipulation of electron wavefunctions through linear and orbital momentum transfer. Here, by introducing phase offset between two orthogonally polarized laser pulses exciting a gold nanorod, we generate a rotating plasmonic near‐field dipole with clockwise and counterclockwise circulating orientations and investigate its interaction with a slow electron beam. Our findings reveal that the circulation direction of plasmonic fields plays a crucial role in modulating electron dynamics, enhancing coupling strength, and controlling recoil. Furthermore, synchronizing the interaction time of the electron beam with rotational dipolar plasmonic resonances results in significant transfer of angular momentum to the electron beams and deflects the electron wavepackets from their original trajectory. These findings highlight the potential of plasmon rotors for shaping electron wavepackets, offering promising applications in ultrafast microscopy, spectroscopy, and quantum information processing.

The interaction between free electrons and laser-induced near-fields provides a platform to study ultrafast processes and quantum phenomena while enabling precise manipulation of electron wavefunctions through linear and orbital momentum transfer. Here, by introducing phase offset between two orthogonally polarized laser pulses exciting a gold nanorod, we generate a rotating plasmonic nearfield dipole with clockwise and counterclockwise circulating orientations and investigate its interaction with a slow electron beam. Our findings reveal that the circulation direction of plasmonic fields plays a crucial role in modulating electron dynamics, enhancing coupling strength, and controlling recoil. Furthermore, synchronizing the interaction time of the electron beam with rotational dipolar plasmonic resonances results in significant transfer of angular momenta to the electron beams and deflects the electron wavepackets from their original trajectory. These findings highlight the potential of plasmon rotors for shaping electron wavepackets, offering promising applications in ultrafast microscopy, spectroscopy, and quantum information processing.

Recent progress in manufacturing high-electron-mobility transistors and optoelectronic devices highlights the necessity of understanding the charge dynamics and its impact on the optical properties inside heterostructures. Herein, we study the optical properties of GaN / A l 0.23 G a 0.77 N / GaN heterostructures using cathodoluminescence (CL) and photoluminescence (PL) spectroscopy. We explore the influence of generated secondary carriers after electron illumination and their penetration depth on the luminescence spectra. Our findings indicate that a higher laser power intensifies the PL response and establishes Fabry–Perot-like resonances. Furthermore, the intensity of the CL response shows a linear behavior versus the acceleration voltage and the current of electron beams for the yellow luminescence peak. A near-infrared CL peak (740 nm) is observed only when illuminating the sample with high currents that is attributed to the trapping of the secondary electrons within the Schottky barrier and the manipulation of the two-dimensional electron gas and the quantum-confined states within the barrier. Self-consistent Poisson–Schrödinger simulations verify this aspect. This research unveils the intricate charge dynamics associated with the interaction of electron beams with heterostructure systems, paving the way for innovative optoelectronic applications in semiconductor devices.

Recent progress in manufacturing high-electron-mobility transistors and optoelectronic devices highlights the necessity of understanding the charge dynamics and its impact on the optical properties inside heterostructures. Herein, we study the optical properties of GaN/AlGaN/GaN heterostructures using cathodoluminescence and photoluminescence spectroscopy. We explore the influence of generated secondary carriers after electron illumination and their penetration depth on the luminescence spectra. Our findings indicate that a higher laser power intensifies the photoluminescence response and establishes Fabry-Perot-like resonances. Furthermore, the intensity of the cathodoluminescence response shows a linear behavior versus the acceleration voltage and the current of electron beams for the yellow luminescence peak. A near-infrared cathodoluminescence peak (740 nm) is observed only when illuminating the sample with high currents that is attributed to the trapping of the secondary electrons within the Schottky barrier and the manipulation of the two-dimensional electron gas and the quantum-confined states within the barrier. Self-consistent Poisson-Schrödinger simulations verify this aspect. This research unveils the intricate charge dynamics associated with the interaction of electron beams with heterostructure systems, paving the way for innovative optoelectronic applications in semiconductor devices.

Recent progress in coherent quantum interactions between free-electron pulses and laser-induced near-field light have revolutionized electron wavepacket shaping. Building on these advancements, we numerically explore the potential of sequential interactions between slow electrons and localized dipolar plasmons in a sequential phase-locked interaction scheme. Taking advantage of the prolonged interaction time between slow electrons and optical near-fields, we aim to explore the effect of plasmon dynamics on the free-electron wavepacket modulation. Our results demonstrate that the initial optical phase of the localized dipolar plasmon at the starting point of the interaction, along with the phase offset between the interaction zones, can serve as control parameters in manipulating the transverse and longitudinal recoil of the electron wavefunction. Moreover, it is shown that the incident angle of the laser light is an additional control knop for tailoring the longitudinal and transverse recoils. We show that a sequential phase-locking method can be employed to precisely manipulate the longitudinal and transverse recoil of the electron wavepacket, leading to selective acceleration or deceleration of the electron energy along specific diffraction angles. These findings have important implications for developing novel techniques for ultrafast electron-light interferometry, shaping the electron wavepacket, and quantum information processing.

Recent progress in coherent quantum interactions between free-electron pulses and laser-induced near-field light have revolutionized electron wavepacket shaping. Building on these advancements, we numerically explore the potential of sequential interactions between slow electrons and localized dipolar plasmons in a sequential phase-locked interaction scheme. Taking advantage of the prolonged interaction time between slow electrons and optical near-fields, we aim to explore the effect of plasmon dynamics on the free-electron wavepacket modulation. Our results demonstrate that the initial optical phase of the localized dipolar plasmon at the starting point of the interaction, along with the phase offset between the interaction zones, can serve as control parameters in manipulating the transverse and longitudinal recoil of the electron wavefunction. Moreover, it is shown that the polarization state of light is an additional control knop for tailoring the longitudinal and transverse recoils. We show that a sequential phase-locking method can be employed to precisely manipulate the longitudinal and transverse recoil of the electron wavepacket, leading to selective acceleration or deceleration of the electron energy along specific diffraction angles. These findings have important implications for the development of novel techniques for ultrafast electron-light interferometry, shaping the electron wave packet, and quantum information processing.

Inelastic interaction of free-electrons with optical near fields has recently attracted attention for manipulating and shaping free-electron wavepackets. Understanding the nature and the dependence of the inelastic cross section on the polarization of the optical near-field is important for both fundamental aspects and the development of new applications in quantum-sensitive measurements. Here, we investigate the effect of the polarization and the spatial profile of plasmonic near-field distributions on shaping free-electrons and controlling the energy transfer mechanisms, but also tailoring the electron recoil. We particularly show that polarization of the exciting light can be used as a control knop for disseminating the acceleration and deceleration path ways via the experienced electron recoil. We also demonstrate the possibility of tailoring the shape of the localized plasmons by incorporating specific arrangements of nanorods to enhance or hamper the transversal and longitudinal recoils of free-electrons. Our findings open up a route towards plasmonic near-fields-engineering for the coherent manipulation and control of slow electron beams for creating desired shapes of electron wavepackets.

Cherenkov radiation (CR) from electrons propagating in materials with a high refractive index have applications in particle-detection mechanisms and could be used for high-yield coherent electron beam-driven photon sources. However, the theory of the CR has been treated up to now using the non-recoil approximation, which neglects the effect of electron deceleration in materials. Here, we report on the effect of electron-beam deceleration on the radiated spectrum and exciton-photon interactions in nm-thick WSe₂ crystals. The calculation of the CR is performed by simulating the kinetic energy of an electron propagating in a thick sample using the Monto Carlo method combined with the Lienard–Wiechert retarded potential. Using this approach, we numerically investigate the interaction between the excitons and generated photons (CR) beyond the non-recoil approximation and are able to reproduce experimental cathodoluminescence spectra. Our findings pave the way for an accurate design of particle scintillators and detectors, based on the strong-coupling phenomenon.