arXiv subjects

Marius Constantin Chirita Mihaila

Publications and source records attributed to Marius Constantin Chirita Mihaila.

10 recordsLinked to original sources

arXiv2026

Coherent regime of Kapitza-Dirac effect with electrons

Electron matter waves coherently diffract when passing through a periodic structure of light formed by two interfering light waves. In this so-called Kapitza-Dirac effect, the electron momentum changes due to absorption and emission of photons via stimulated Compton scattering. Until now, the effect has only been observed with low energy electrons due to the small momentum of a visible photon compared to the momentum of high energy electron leading to diffraction angles of 10^(-4) rad or smaller. We report on the observation of the Kapitza-Dirac effect in a scanning electron microscope using high energy (20 and 30 keV) electrons with de-Broglie wavelengths of 9 pm and 7 pm, respectively. The photon sidebands in the electron transverse momentum spectrum are detected in the convergent beam diffraction geometry using spatial filtering. As the coupling strength between the electrons and the light field increases, the sideband populations exhibit coherent, reversible oscillations among diffraction orders. The effect can serve as a coherent electron beam-splitter or a phase-plate in various types of electron microscopes.

quant-ph↗

arXiv2026

Transverse Modulation of Continuous Electron Beams by a Structured Optical Cavity

Compact aberration correction at large semi-angles remains a central challenge in electron microscopy. Here we propose a phase plate for continuous electron beams based on the ponderomotive interaction with an intracavity standing wave in a near-concentric Fabry--Pérot resonator. For electrons propagating along the cavity axis, a standing-wave with Laguerre-Gaussian mode of topological charge $l=1$ imprints an annular phase shift that is opposite in sign to the third-order spherical aberration of a conventional electron lens. For a $5~\mathrm{keV}$ beam with a convergence semi-angle of $25~\mathrm{mrad}$, we fully compensate the third-order spherical aberration of an objective lens with $C_\mathrm{s}=1~\mathrm{mm}$, yielding the transverse width of the corrected probe in the focus of $σ_\mathrm{p}=1.4~\mathrmÅ$. The accessible transverse electron phases are set by the supported resonator modal basis and its coherent superpositions.

physics.optics↗

arXiv2026

Independent amplitude and phase control using a single phase-only SLM

Liquid-crystal spatial light modulators (SLMs) are widely used for programmable wavefront control but are typically operated as phase-only devices, limiting applications that require independent amplitude and phase shaping. Here we demonstrate full complex-field modulation using a single phase-only SLM by implementing two sequential modulation planes on different regions of the same device. The phase retardance introduced by the first SLM region is converted into amplitude modulation by a polarizer placed in the beam path, while the second region compensates the associated phase offset and imposes the required phase distribution. The field from the first region is imaged onto the second, enabling complex-field synthesis without a second modulator. We validate the approach by generating Bessel--Gaussian beams, helical-phase fields, and arbitrary focal-plane intensity patterns. This single-SLM platform provides a compact route to programmable complex wavefront engineering for structured illumination, holography, and electron--light interaction experiments.

physics.optics↗

arXiv2025

Light-based electron aberration corrector

Achieving atomic resolution in electron microscopy has historically been hindered by spherical aberration, a fundamental limitation of conventional electron lenses. Its correction typically requires complex assemblies of electromagnetic multipoles. Here, we demonstrate that spherical aberration in a cylindrically symmetric electron lens can be fully compensated via interaction with a shaped light field. By analyzing distortions in high-magnification point-projection electron images of optical standing waves, we quantify the spherical aberration before and after light-induced correction. This approach introduces a new paradigm for optical control in electron beam shaping and opens a pathway towards compact and tunable light-based aberration correctors for high-resolution electron microscopy.

physics.optics↗

arXiv2025

Ultrafast 4D scanning transmission electron microscopy for imaging of localized optical fields

Ultrafast electron microscopy aims for imaging transient phenomena occurring on nanoscale. One of its goals is to visualize localized optical and plasmonic modes generated by coherent excitation in the vicinity of various types of nanostructures. Such imaging capability was enabled by photoninduced near-field optical microscopy, which is based on spectral filtering of electrons inelastically scattered due to the stimulated interaction with the nearfield. Here, we report on the development of ultrafast four-dimensional (4D) scanning transmission electron microscopy, which allows us to image the transverse components of the optical near-field while avoiding the need of electron spectral filtering. We demonstrate that this method is capable of imaging the integrated Lorentz force generated by optical near-fields of a tungsten nanotip and the ponderomotive potential of an optical standing wave with a spatial resolution of 21 nm.

physics.optics↗

arXiv2025

Temporal characterization of femtosecond electron pulses inside ultrafast scanning electron microscope

In this work, we present the implementation of all-optical method for directly measuring electron pulse duration in an ultrafast scanning electron microscope. Our approach is based on the interaction of electrons with the ponderomotive potential of an optical standing wave and provides a precise in situ technique to characterize femtosecond electron pulses at the interaction region across a wide range of electron energies (1-30 keV). By using single-photon photoemission of electrons by ultraviolet femtosecond laser pulses from a Schottky emitter we achieve electron pulse durations ranging from 0.5 ps at 30 keV to 2.7 ps at 5.5 keV under optimal conditions where Coulomb interactions are negligible. Additionally, we demonstrate that reducing the photon energy of the femtosecond pulses used for photoemission from 4.8 eV (257.5 nm) to 2.4 eV (515 nm) decreases the initial energy spread of emitted electrons, leading to significantly shorter pulse durations, particularly at lower electron energies.

physics.optics↗

arXiv2025

Light-based Chromatic Aberration Correction of Ultrafast Electron Microscopes

We propose and theoretically demonstrate a technique that allows one to compensate for chromatic aberrations of traditional electron lenses in ultrafast electron microscopes. The technique is based on space- and time-dependent phase modulation of a pulsed electron beam using interaction with a shaped pulsed ponderomotive lens. The energy-selective focal distance is reached by combining the electron temporal chirp with the time-dependent size of the effective potential, with which the electrons interact. As a result, chromatic aberration can be reduced by up to a factor of seven. This approach paves the way for advanced transverse and longitudinal wavefront shaping of electrons in free space.

quant-ph↗

arXiv2025

Design for light-based spherical aberration correction of ultrafast electron microscopes

We theoretically demonstrate that ponderomotive interactions near the electron cross-over can be used for aberration correction in ultrafast electron microscopes. Highly magnified electron shadow images from Si$_3$N$_4$ thin films are utilized to visualize the distortions induced by spherical aberrations. Our simulations of electron-light interactions indicate that spherical aberrations can be compensated resulting in an aberration free angle of \SI{8.1}{mrad}. For achieving the necessary light distribution, we use a gradient descent algorithm to optimize Zernike polynomials and shape the light beam into a modified Gaussian and Laguerre-Gaussian beam.

physics.optics↗

arXiv2024

Generation of ultrashort ion pulses from ultrafast electron-stimulated desorption

We present an efficient method to produce laser-triggered proton pulses well below 500 ps pulse width at keV energies. We use femtosecond photoelectron pulses emitted from a cathode to enable ultrafast electron-stimulated desorption of adsorbates on a stainless steel plate under ultrahigh vacuum conditions. While direct photoionization of atoms to form well-timed ion pulses can suffer from a laser-focus-limited large starting volume, in our method the two-dimensional starting plane of the ions is defined with nanometer precision at a solid surface. We clearly outline how the method could be used in the future to efficiently produce ion beam pulses in the (sub)picosecond range for pump-probe experiments with ions.

physics.app-ph↗

arXiv2023

Transverse Electron Beam Shaping with Light

Interfacing electrons and light enables ultrafast electron microscopy, quantum control of electrons, as well as new optical elements for high sensitivity imaging. Here we demonstrate for the first time programmable transverse electron beam shaping in free space based on ponderomotive potentials from short intense laser pulses. We can realize both convex and concave electron lenses with a focal length of a few millimeters, comparable to those in state-of-the-art electron microscopes. We further show that we can realize almost arbitrary deflection patterns by shaping the ponderomotive potentials using a spatial light modulator. Our modulator is lossless, programmable, has unity fill factor, and could pave the way to electron wavefront shaping with hundreds of individually addressable pixels.

physics.optics↗