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Vortex-carrying matter waves, such as chiral electron beams, are of significant interest in both applied and fundamental science. Continuous-wave electron vortex beams are commonly prepared via passive phase masks imprinting a transverse phase modulation on the electron’s wavefunction. Here, we show that femtosecond chiral plasmonic near fields enable the generation and dynamic control on the ultrafast timescale of an electron vortex beam. The vortex structure of the resulting electron wavepacket is probed in both real and reciprocal space using ultrafast transmission electron microscopy. This method offers a high degree of scalability to small length scales and a highly efficient manipulation of the electron vorticity with attosecond precision. Besides the direct implications in the investigation of nanoscale ultrafast processes in which chirality plays a major role, we further discuss the perspectives of using this technique to shape the wavefunction of charged composite particles, such as protons, and how it can be used to probe their internal structure.

Light-electron interaction is the seminal ingredient in free-electron lasers and dynamical investigation of matter. Pushing the coherent control of electrons by light to the attosecond timescale and below would enable unprecedented applications in quantum circuits and exploration of electronic motions and nuclear phenomena. Here we demonstrate attosecond coherent manipulation of a free-electron wave function, and show that it can be pushed down to the zeptosecond regime. We make a relativistic single-electron wavepacket interact in free-space with a semi-infinite light field generated by two light pulses reflected from a mirror and delayed by fractions of the optical cycle. The amplitude and phase of the resulting electron-state coherent oscillations are mapped in energy-momentum space via momentum-resolved ultrafast electron spectroscopy. The experimental results are in full agreement with our analytical theory, which predicts access to the zeptosecond timescale by adopting semi-infinite X-ray pulses.

Recent experiments have shown that by combining a femtosecond laser with an electron microscope, dynamics at the nanoscale with femtosecond temporal resolution can be followed. These ultrafast electron microscopy (UEM) techniques have allowed a variety of experimental studies on nanoscale material systems to be conducted, including the ability to image plasmon dynamics in real time. We will discuss how UEM can also be used to study fundamental quantum problems, present some recent experimental results and we will discuss how future experimental improvements will push the temporal resolution from hundreds of femtoseconds down to the single femtosecond regime and below.

An electron beam traversing a structured plasmonic field is shown to undergo diffraction with characteristic angular patterns of both elastic and inelastic outgoing electron components. In particular, a plasmonic grating (e.g., a standing wave formed by two counterpropagating plasmons in a thin film) produces diffraction orders of the same parity as the net number of exchanged plasmons. Large diffracted beam fractions are predicted to occur for realistic plasmon intensities in attainable geometries due to a combination of phase and amplitude changes locally imprinted on the passing electron wave. Our study opens vistas in the study of multiphoton exchanges between electron beams and evanescent optical fields with unexplored effects related to the transversal component of the electron wave function.

Capturing and controlling plasmons at buried interfaces with nanometre and femtosecond resolution has yet to be achieved and is critical for next generation plasmonic devices. Here we use light to excite plasmonic interference patterns at a buried metal-dielectric interface in a nanostructured thin film. Plasmons are launched from a photoexcited array of nanocavities and their propagation is followed via photon-induced near-field electron microscopy (PINEM). The resulting movie directly captures the plasmon dynamics, allowing quantification of their group velocity at ∼0.3 times the speed of light, consistent with our theoretical predictions. Furthermore, we show that the light polarization and nanocavity design can be tailored to shape transient plasmonic gratings at the nanoscale. This work, demonstrating dynamical imaging with PINEM, paves the way for the femtosecond and nanometre visualization and control of plasmonic fields in advanced heterostructures based on novel two-dimensional materials such as graphene, MoS2, and ultrathin metal films.

We propose an all-optical method of creating electron vortices utilizing the Kapitza-Dirac effect. This technique uses the transfer of orbital angular momentum from photons to free electrons creating electron vortex beams in the process. The laser intensities needed for this experiment can be obtained with available pulsed lasers and the resulting electron beams carrying orbital angular momentum will be particularly useful in the study of magnetic materials and chiral plasmonic structures in ultrafast electron microscopy.

By combining the techniques of point projection electron microscopy with an ultrafast field emission tip source a simple compact ultrafast electron microscope can be constructed.

Light matter interactions at the nanoscale are fundamental to the rapidly developing fields of plasmonics and nanophotonics. These fields hold the promise of advancing both the speed of computers along with communications and may also provide methods to create a new generation of ultrasensitive molecular biosensors. While there are a variety of techniques that can provide static images of these devices with suboptical wavelength precision there are only a few that are capable of capturing the ultrafast dynamics of electromagnetic fields interacting with or produced by nanomaterials. In this Perspective, we aim to introduce the reader to the newly developed field of 4D ultrafast electron microscopy (4D UEM), which provides a unique window into ultrafast dynamics at the nanoscale. We will describe the basic technique and how internal structural, bulk electronic, and surface near-field dynamics can all be obtained with nanometer and femtosecond resolutions. In addition, we will discuss how a variety of different ultrafast electron microscopes have been used to map the evolution of photonics-related phenomena. Throughout, we discuss the direction of research that will help advance the understanding of light matter interactions near the atomic scale in both space and time.

Surface plasmon polaritons can confine electromagnetic fields in subwavelength spaces and are of interest for photonics, optical data storage devices and biosensing applications. In analogy to photons, they exhibit wave-particle duality, whose different aspects have recently been observed in separate tailored experiments. Here we demonstrate the ability of ultrafast transmission electron microscopy to simultaneously image both the spatial interference and the quantization of such confined plasmonic fields. Our experiments are accomplished by spatiotemporally overlapping electron and light pulses on a single nanowire suspended on a graphene film. The resulting energy exchange between single electrons and the quanta of the photoinduced near-field is imaged synchronously with its spatial interference pattern. This methodology enables the control and visualization of plasmonic fields at the nanoscale, providing a promising tool for understanding the fundamental properties of confined electromagnetic fields and the development of advanced photonic circuits.

By utilizing a nanometer ultrafast electron source in a point projection microscope we demonstrate that images of nanoparticles with spatial resolutions of the order of 100 nanometers can be obtained. The duration of the emission process of the photoemitted electrons used to make images is shown to be of the order of 100 fs using an autocorrelation technique. The compact geometry of this photoelectron point projection microscope does not preclude its use as a simple ultrafast electron microscope, and we use simple analytic models to estimate temporal resolutions that can be expected when using it as a pump-probe ultrafast electron microscope. These models show a significant increase in temporal resolution when comparing to ultrafast electron microscopes based on conventional designs. We also model the microscopes spectroscopic abilities to capture ultrafast phenomena such as the photon induced near field effect.

In this paper, the design and implementation of a femtosecond-resolved ultrafast transmission electron microscope is presented, based on a thermionic gun geometry. Utilizing an additional magnetic lens between the electron acceleration and the nominal condenser lens system, a larger percentage of the electrons created at the cathode are delivered to the specimen without degrading temporal, spatial and energy resolution significantly, while at the same time maintaining the femtosecond temporal resolution. Using the photon-induced near field electron microscopy effect (PINEM) on silver nanowires the cross-correlation between the light and electron pulses was measured, showing the impact of the gun settings and initiating laser pulse duration on the electron bunch properties. Tuneable electron pulses between 300fs and several ps can be obtained, and an overall energy resolution around 1eV was achieved.

Advances in the imaging of biological structures with transmission electron microscopy continue to reveal information at the nanometer length scale and below. The images obtained are static, i.e., time-averaged over seconds, and the weak contrast is usually enhanced through sophisticated specimen preparation techniques and/or improvements in electron optics and methodologies. Here we report the application of the technique of photon-induced near-field electron microscopy (PINEM) to imaging of biological specimens with femtosecond (fs) temporal resolution. In PINEM, the biological structure is exposed to single-electron packets and simultaneously irradiated with fs laser pulses that are coincident with the electron pulses in space and time. By electron energy-filtering those electrons that gained photon energies, the contrast is enhanced only at the surface of the structures involved. This method is demonstrated here in imaging of protein vesicles and whole cells ofEscherichia coli, both are not absorbing the photon energy, and both are of low-Zcontrast. It is also shown that the spatial location of contrast enhancement can be controlled via laser polarization, time resolution, and tomographic tilting. The high-magnification PINEM imaging provides the nanometer scale and the fs temporal resolution. The potential of applications is discussed and includes the study of antibodies and immunolabeling within the cell.

Un procede permettant d'obtenir des images PINEM consiste a utiliser une impulsion optique d'une femtoseconde, a generer des impulsions electroniques, et a diriger ces impulsions electroniques vers un echantillon. Ce procede consiste egalement a provoquer le chevauchement des impulsions optiques d'une femtoseconde et des impulsions electroniques sur le plan spatial et temporel a l'emplacement de l'echantillon, et a transferer aux impulsions electroniques l'energie provenant des impulsions optiques d'une femtoseconde. Ledit procede comprend en outre la detection d'impulsions electroniques ayant une energie superieure a une valeur d'affaiblissement nul, ce qui permet d'obtenir l'imagerie dans l'espace et dans le temps.