arXiv subjects

Giovanni Maria Vanacore

Publications and source records attributed to Giovanni Maria Vanacore.

9 recordsLinked to original sources

arXiv2025

Roadmap for Quantum Nanophotonics with Free Electrons

Over the past century, continuous advancements in electron microscopy have enabled the synthesis, control, and characterization of high-quality free-electron beams. These probes carry an evanescent electromagnetic field that can drive localized excitations and provide high-resolution information on material structures and their optical responses, currently reaching the sub-ångström and few-meV regime. Moreover, combining free electrons with pulsed light sources in ultrafast electron microscopy adds temporal resolution in the sub-femtosecond range while offering enhanced control of the electron wave function. Beyond their exceptional capabilities for time-resolved spectromicroscopy, free electrons are emerging as powerful tools in quantum nanophotonics, on par with photons in their ability to carry and transfer quantum information, create entanglement within and with a specimen, and reveal previously inaccessible details on nanoscale quantum phenomena. This Roadmap outlines the current state of this rapidly evolving field, highlights key challenges and opportunities, and discusses future directions through a collection of topical sections prepared by leading experts.

cond-mat.mes-hall↗

arXiv2025

Realization of a Pre-Sample Photonic-based Free-Electron Modulator in Ultrafast Transmission Electron Microscopes

Spatial and temporal light modulation is a well-established technology that enables dynamic shaping of the phase and amplitude of optical fields, significantly enhancing the resolution and sensitivity of imaging methods. Translating this capability to electron beams is highly desirable within the framework of a transmission electron microscope (TEM) to benefit from the nanometer spatial resolution of these instruments. In this work, we report on the experimental realization of a photonic-based free-electron modulator integrated into the column of two ultrafast TEMs for pre-sample electron-beam shaping. Electron-photon interaction is employed to coherently modulate both the transverse and longitudinal components of the electron wave function, while leveraging dynamically controlled optical fields and tailored design of electron-laser-sample interaction geometry. Using energy- and momentum-resolved electron detection, we successfully reconstruct the shaped electron wave function at the TEM sample plane. These results demonstrate the ability to manipulate the electron wave function before probing the sample, paving the way for the future development of innovative imaging methods in ultrafast electron microscopy.

physics.optics↗

arXiv2024

Coherently amplified ultrafast imaging using a free-electron interferometer

Accessing the low-energy non-equilibrium dynamics of materials and their polaritons with simultaneous high spatial and temporal resolution has been a bold frontier of electron microscopy in recent years. One of the main challenges lies in the ability to retrieve extremely weak signals while simultaneously disentangling amplitude and phase information. Here, we present Free-Electron Ramsey Imaging (FERI), a microscopy approach based on light-induced electron modulation that enables coherent amplification of optical near-fields in electron imaging. We provide simultaneous time-, space-, and phase-resolved measurements of a micro-drum made from a hexagonal boron nitride membrane visualizing the sub-cycle dynamics of 2D polariton wavepackets therein. The phase-resolved measurements reveals vortex-anti-vortex singularities on the polariton wavefronts, together with an intriguing phenomenon of a traveling wave mimicking the amplitude profile of a standing wave. Our experiments show a 20-fold coherent amplification of the near-field signal compared to conventional electron near-field imaging, resolving peak field intensities in the order of ~W/cm2, corresponding to field amplitudes of a few kV/m. As a result, our work paves the way for spatio-temporal electron microscopy of biological specimens and quantum materials, exciting yet delicate samples that are currently difficult to investigate.

physics.optics↗

arXiv2024

Revisiting the excitation of the low-lying $^{181\text{m}}$Ta isomer in optical laser-generated plasma

The excitation of the $^{181\text{m}}$Ta isomer in the laser-plasma scenario was claimed to have been observed more than two decades ago. However, the reported experimental findings - and the respective high excitation rate - were later questioned as they could not be reproduced theoretically. The controversy has remained open ever since. In this work, we reinvestigate both theoretically and experimentally the $^{181\text{m}}$Ta nuclear excitation in an optical laser-generated plasma. Experimentally we have found no evidence for such an excitation process as consistently predicted by previous and our theoretical models.

nucl-ex↗

arXiv2023

Indirect exciton-phonon dynamics in MoS2 revealed by ultrafast electron diffraction

Transition metal dichalcogenides layered nano-crystals are emerging as promising candidates for next-generation optoelectronic and quantum devices. In such systems, the interaction between excitonic states and atomic vibrations is crucial for many fundamental properties, such as carrier mobilities, quantum coherence loss, and heat dissipation. In particular, to fully exploit their valley-selective excitations, one has to understand the many-body exciton physics of zone-edge states. So far, theoretical and experimental studies have mainly focused on the exciton-phonon dynamics in high-energy direct excitons involving zone-center phonons. Here, we use ultrafast electron diffraction and ab initio calculations to investigate the many-body structural dynamics following nearly-resonant excitation of low-energy indirect excitons in MoS2. By exploiting the large momentum carried by scattered electrons, we identify the excitation of in-plane K- and Q-phonon modes with E^' symmetry as key for the stabilization of indirect excitons generated via near-infrared light at 1.55 eV, and we shed light on the role of phonon anharmonicity and the ensuing structural evolution of the MoS2 crystal lattice. Our results highlight the strong selectivity of phononic excitations directly associated with the specific indirect-exciton nature of the wavelength-dependent electronic transitions triggered in the system.

cond-mat.mes-hall↗

arXiv2023

Free-Electron Ramsey-Type Interferometry for Enhanced Amplitude and Phase imaging of Nearfields

The complex range of interactions between electrons and electromagnetic fields gave rise to countless scientific and technological advances. A prime example is photon-induced nearfield electron microscopy (PINEM), enabling the detection of confined electric fields in illuminated nanostructures with unprecedented spatial resolution. However, PINEM is limited by its dependence on strong fields, making it unsuitable for sensitive samples, and its inability to resolve complex phasor information. Here, we leverage the nonlinear, over-constrained nature of PINEM to present an algorithmic microscopy approach, achieving far superior nearfield imaging capabilities. Our algorithm relies on free-electron Ramsey-type interferometry to produce orders-of-magnitude improvement in sensitivity and ambiguity-immune nearfield phase reconstruction, both of which are optimal when the electron exhibits a fully quantum behavior. Our results demonstrate the potential of combining algorithmic approaches with novel modalities in electron microscopy, and may lead to various applications from imaging sensitive biological samples to performing full-field tomography of confined light.

physics.optics↗

arXiv2022

Single-Pixel Imaging in Space and Time with Optically-Modulated Free Electrons

Single-pixel imaging, originally developed in light optics, facilitates fast three-dimensional sample reconstruction, as well as probing with light wavelengths undetectable by conventional multi-pixel detectors. However, the spatial resolution of optics-based single-pixel microscopy is limited by diffraction to hundreds of nanometers. Here, we propose an implementation of single-pixel imaging relying on attainable modifications of currently available ultrafast electron microscopes in which optically-modulated electrons are used instead of photons to achieve sub-nanometer spatially- and temporally-resolved single-pixel imaging. We simulate electron beam profiles generated by interaction with the optical field produced by an externally programable spatial light modulator and demonstrate the feasibility of the method by showing that the sample image and its temporal evolution can be reconstructed using realistic imperfect illumination patterns. Electron single-pixel imaging holds strong potential for application in low-dose probing of beam-sensitive biological and molecular samples, including rapid screening during in-situ experiments.

physics.optics↗

arXiv2022

Charge dynamics electron microscopy: nanoscale imaging of femtosecond plasma dynamics

Understanding and actively controlling the spatio-temporal dynamics of non-equilibrium electron clouds is fundamental for the design of light and electron sources, novel high-power electronic devices, and plasma-based applications. However, electron clouds evolve in a complex collective fashion on nanometer and femtosecond scales, producing electromagnetic screening that renders them inaccessible to existing optical probes. Here, we solve the long-standing challenge of characterizing the evolution of electron clouds generated upon irradiation of metallic structures using an ultrafast transmission electron microscope to record the charged plasma dynamics. Our approach to charge dynamics electron microscopy (CDEM) is based on the simultaneous detection of electron-beam acceleration and broadening with nanometer/femtosecond resolution. By combining experimental results with comprehensive microscopic theory, we provide deep understanding of this highly out-of-equilibrium regime, including previously inaccessible intricate microscopic mechanisms of electron emission, screening by the metal, and collective cloud dynamics. Beyond the present specific demonstration, the here introduced CDEM technique grants us access to a wide range of non-equilibrium electrodynamic phenomena involving the ultrafast evolution of bound and free charges on the nanoscale.

physics.app-ph↗

arXiv2022

Ultrafast Electron Microscopy of Nanoscale Charge Dynamics in Semiconductors

The ultrafast dynamics of charge carriers in solids plays a pivotal role in emerging optoelectronics, photonics, energy harvesting, and quantum technology applications. However, the investigation and direct visualization of such non-equilibrium transport phenomena remains as a long-standing challenge, owing to the nanometer-femtosecond spatio-temporal scales at which the charge carriers evolve. Here, we propose and demonstrate a novel interaction mechanism enabling nanoscale imaging of the femtosecond dynamics of charge carriers in solids. This imaging modality, which we name charge dynamics electron microscopy (CDEM), exploits the strong interaction between terahertz (THz) electromagnetic near fields produced by the moving charges and synchronized free-electron pulses in an ultrafast scanning transmission electron microscope. The measured free-electron energy at different spatio-temporal coordinates allows us to directly retrieve the THz near-field amplitude and phase, from which we reconstruct movies of the generated charges by comparison with microscopic theory. The introduced CDEM technique thus allows us to investigate previously inaccessible spatio-temporal regimes of charge dynamics in solids, for example revealing new insight into the photo-Dember effect, showing oscillations of photo-generated electron-hole distributions inside a semiconductor. Our work lays the foundation for exploring a wide range of previously inaccessible charge-transport phenomena in condensed matter using ultrafast electron microscopy.

cond-mat.mes-hall↗