arXiv subjects

Petr Koutenský

Publications and source records attributed to Petr Koutenský.

7 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

Imaging the transverse component of optical near-fields in resonant photonic structures

We report on imaging the optical near-fields in resonant periodic photonic structures with nanometer resolution using ultrafast 4D scanning transmission electron microscopy (U4DSTEM). In particular, U4DSTEM is applied to visualize the transverse component of the Lorentz force of a synchronous near-field mode excited by an infrared femtosecond pulse in a periodic silicon nanostructure designed for photonic acceleration of electrons. Our results show that in addition to the accelerating/decelerating force acting on the electrons in the longitudinal direction along the electron propagation, the structures can be efficiently used for transverse electron streaking at optical frequencies when excited by light with polarization perpendicular to the electron trajectory. The measured spatial profile of the excited near-field mode intensity is consistent with the numerical simulations performed using finite-difference time domain technique.

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

Electron vortex beams for chirality probing at the nanoscale

In this work we propose a method for probing the chirality of nanoscale electromagnetic near fields utilizing the properties of a coherent superposition of free-electron vortex states in electron microscopes. Electron beams optically modulated into vortices carry orbital angular momentum, thanks to which they are sensitive to the spatial phase distribution and topology of the investigated field. The sense of chirality of the studied specimen can be extracted from the spectra of the electron beam with nanoscale precision owing to the short picometer de Broglie wavelength of the electron beam. We present a detailed case study of the interaction of a coherent superposition of electron vortex states and the optical near field of a golden nanosphere illuminated by circularly polarized light as an example, and we examine the chirality sensitivity of electron vortex beams on intrinsically chiral plasmonic nanoantennae.

physics.optics↗

arXiv2025

Monochromatization of Electron Beams with Spatially and Temporally Modulated Optical Fields

Inelastic interaction between coherent light with constant frequency and free electrons enables periodic phase modulation of electron wave packets leading to periodic side-bands in the electron energy spectra. In this Letter we propose a generalization of the interaction by considering linearly chirped electron wave packets interacting with chirped optical fields. We theoretically demonstrate that when matching the chirp parameters of the electron and light waves, the interaction leads to partial monochromatization of the electron spectra in one of the energy side-bands. Depending on the coherence time of the electrons, the electron spectrum may be narrowed down by a factor of 5-times with 26% of the electron distribution in the monochromatized energy band. This approach will improve the spectral resolution and reduce color aberrations in ultrafast imaging experiments with free electrons.

physics.optics↗