The pulse-averaged effects of Coulomb interactions from such sources have recently been investigated, and are associated with spectral broadening and a loss of temporal and spatial resolution 17, 34, 35, 36.Įmploying concepts from quantum optics 37, correlations among free electrons have previously been identified by coincidence detection using detector pairs 20, 21, 22, 38, as in atomic and molecular science measuring electrons and ions 39, 40, correlated photoemission 41, 42, 43 and ionization 44, 45. Strong interparticle interactions are enabled by spatiotemporally confined femtosecond-pulsed photoemission from nanotips 25, 26, 27, 28, 29, 30, 31, 32, employed for ultrafast electron microscopy and diffraction with high-coherence beams 13, 16, 33. Tailoring such correlations in free-electron beams facilitates sub-Poissonian beam statistics 22, promising shot-noise-reduced imaging and lithography. 20, has been a long-standing question and is still actively discussed in the context of exchange-mediated 21 and Coulomb 23, 24 interactions.
In particular, the physical origin of antibunching in free-electron beams, as reported by Kiesel et al. Field emitters represent highly localized sources, and they have been used in studies elucidating free-electron correlations 20, 21, 22. Studying strong electronic correlations in a beam containing only a few particles requires the preparation of a sufficient electron phase space degeneracy. In high-charge electron pulses for time-resolved experiments, mean-field and stochastic Coulomb effects govern the achievable pulse duration, energy spread and focusability, and pose a major experimental challenge for ultrafast electron diffraction 9, 10, 11, 12, 13, 14 and microscopy 15, 16, 17, particle accelerators 18 and free-electron lasers 19. In electron microscopy, electron repulsion leads to stochastic longitudinal and transverse emittance growth of the beam, described by the Boersch 5 and Loeffler 6 effects, respectively, and limiting the brightness of state-of-the-art electron sources 7, 8. In contrast to the opportunities offered by electron correlations in condensed matter, Coulomb interactions in free-electron beams are usually considered to have adverse effects. Mediated by the Coulomb force, few- and many-body electronic correlations govern intriguing phases of matter, such as superconductivity or charge ordering, and they underpin a wide variety of applications down to nanoscale single-electron sources 1, 2 and logic gates based on single charges 3, 4. In this way, the fraction of specific few-electron states can be actively suppressed or enhanced, facilitating the preparation of highly non-Poissonian electron beams for microscopy and lithography, including future heralding schemes and correlated multi-electron probing.Ĭorrelations between electrons are at the core of numerous phenomena in atomic, molecular and solid-state physics. The pronounced spatial and spectral characteristics of these electron number states allow filtering schemes that control the statistical distribution of the pulse charge. We observe field-controllable electron antibunching, attributed primarily to transverse Coulomb deflection. State-sorted beam caustics show a discrete increase in virtual source size and longitudinal source shift for few-electron states, associated with transverse momentum correlations.
We identify distinctive energy and momentum correlations arising from acceleration-enhanced interparticle energy exchange, revealing strong few-body Coulomb interactions at an energy scale of 2 eV. Event-based electron spectroscopy allows the spatial and spectral characterization of the electron ensemble emitted by each laser pulse. Here, we demonstrate the generation of Coulomb-correlated pair, triple and quadruple states of free electrons by femtosecond photoemission from a nanoscale field emitter inside a transmission electron microscope. While correlated electrons are at the heart of many phenomena in condensed matter, as well as atomic and molecular physics, Coulomb interactions in free-electron beams are generally considered detrimental.
0 kommentar(er)
