Spatio-temporal shaping of electron wavepackets for time-domain electron holography

Projektinformationen

eWaveShaper

ID Finanzhilfevereinbarung: 101039339

DOI

10.3030/101039339

EK-Unterschriftsdatum 1 April 2022

Startdatum 1 Januar 2023

Enddatum 31 Dezember 2027

Finanziert unter

• European Research Council (ERC)

Gesamtkosten

€ 1 835 895,00

EU-Beitrag

€ 1 835 895,00

Koordiniert durch

UNIVERZITA KARLOVA
Czechia

Periodic Reporting for period 1 - eWaveShaper (Spatio-temporal shaping of electron wavepackets for time-domain electron holography)

Berichtszeitraum: 2023-01-01 bis 2025-06-30

Zusammenfassung vom Kontext und den Gesamtzielen des Projekts

Approximately half a century ago, electron microscopy opened a window into the nanoworld. Imaging individual nano-objects and even atoms within materials has now become routine. Beyond static imaging, ultrafast electron microscopy aims to extend the capabilities of conventional microscopes into the time domain. Achieving complex spatio-temporal imaging requires innovative methodologies that enable precise control of electron beams on ultrafast timescales while maintaining high spatial resolution.

This project has three primary objectives. The first is to develop advanced methods for spatio-temporal shaping of electron beams using the ponderomotive potential of electromagnetic fields generated by pulsed lasers. Such tailored electron beams will be employed in various experiments. The second goal is to explore the transfer of coherence imprinted by optical fields to electrons, with the aim of producing coherent photon emission through the process of coherent cathodoluminescence. Additionally, we will investigate the potential for temporally shaped electron pulses—containing multiple electrons—to coherently excite two-level quantum systems. The third objective is to demonstrate a novel form of spatio-temporal electron holography, an interferometric technique capable of reconstructing the amplitude and phase of optical or plasmonic near-fields generated by coherent illumination of nanostructures.

The outcomes of this research will advance the field of time-resolved electron microscopy, providing new methods to observe ultrafast electronic dynamics and the spatial-temporal evolution of electromagnetic fields with nanometer spatial and attosecond temporal resolutions. Furthermore, the project may have significant technological implications for electron microscopy, with some methods potentially leading to commercial applications.

Arbeit, die ab Beginn des Projekts bis zum Ende des durch den Bericht erfassten Berichtszeitraums geleistet wurde, und die wichtigsten bis dahin erzielten Ergebnisse

We theoretically investigated several aspects of the interaction between shaped light fields and electrons for manipulation with electron wave function. First we studied the possibility to utilize time-structured electron vortex states for imaging of chiral optical near-fields. We proposed a novel method generalizing the electron-photon interaction to the case of light with temporally-dependent frequency, which allows, e.g. to monochromatize a pulsed electron beam. Further we theoretically investigated various geometries allowing to demonstrate aberration correction of electron optics using the interaction of electrons with spatially shaped optical beams. We investigated the regime of electron-photon interactions beyond the non-recoil approximation, where we expect focusing of electrons in momentum space.

In the experimental part we focused on the characterization of ultrashort electron pulse characterization in different photoemission regimes of the electron microscope. We studied the quantum aspects of the interaction between electrons and photons in free space using the transverse Kapitza-Dirac effects, which we observed for the fist time with fast 20 keV electrons (this effect was previously only demonstrated with slow electrons) based on convergent electron beam diffraction. We developed and demonstrated a novel method allowing to image optical near-fields in a SEM using ultrafast 4D scanning electron microscopy. This method brings an alternative to photon-induced near-field electron microscopy, which requires electron spectrometer and which is only sensitive to the component of the optical near-field in the propagation direction of the electrons.This technique allows to image the transverse components of the optical near-field without the need of an electron spectrometer or energy filter. Further we for the first time experimentally demonstrated correction of spherical aberration of electron lens using shaped light fields.

On top of the planned theoretical studies and experiments, the work on the project led us to different ideas related to control of the electron wave function in condensed matter using the interaction with nonresonant light fields. We developed a novel scheme allowing to generate valley polarized electron population in crystalline silicon and diamond at room temperature using femtosecond optical pulses. Valley quantum number is an alternative to electron charge and spin that can be utilized for information storage and processing. Such control of electron momentum state in solids may thus bring valleytronics – the new type of ultrafast electronics - closer to its real applications in technologically important materials.

Fortschritte, die über den aktuellen Stand der Technik hinausgehen und voraussichtliche potenzielle Auswirkungen (einschließlich der bis dato erzielten sozioökonomischen Auswirkungen und weiter gefassten gesellschaftlichen Auswirkungen des Projekts)

1) We developed a new approach allowing to image the optical or plasmonic near-field generated in the vicinity of nanostructures with sub-wavelength spatial resolution using ultrafast 4D scanning transmission electron microscopy. This method allows to visualize the transverse component of the Lorentz force of the optical field by measuring elastic scattering of electrons (deflection) in contrast to previously demonstrated photon-induced near-field electron microscopy, which is based on filtering the inelastically scattered electrons using an electron spectrometer. This method represents a novel approach, which can be implemented in widely used scanning electron microscopes and which may find wide applications in the fields of nanophotonics, plasmonics and metamaterial research.

2) We developed a new experimental method allowing to control the wave vector of electrons in bulk crystalline semiconductors by the interaction with nonresonant ultrashort laser pulses. We showed that the method allows to create valley-polarized populations of electrons in silicon and diamond. The valley quantum number has a potential to replace electron charge and may be applied in future high-speed and low-power consumption quantum information technologies.

3) We theoretically investigated aberration correction of different types of electron lens aberrations using ponderomotive interaction of electrons with shaped light fields. For the first time we experimentally demonstrated that the third-order spherical aberration of electron lens can be compensated by the interaction with shaped light.

Ultrafast electron microscope setup used to perform the experiments within eWaveShaper project