Attosecond Electron Pulse Trains Research Articles

Tailored high-contrast attosecond electron pulses for coherent excitation and scattering

Temporally shaping the density of electron beams using light forms the basis for a wide range of established and emerging technologies, including free-electron lasers and attosecond electron microscopy. The modulation depth of compressed electron pulses is a key figure of merit limiting applications. In this work, we present an approach for generating background-free attosecond electron pulse trains by sequential inelastic electron-light scattering. Harnessing quantum interference in the fractional Talbot effect, we suppress unwanted background density in electron compression by several orders of magnitude. Our results will greatly enhance applications of coherent electron-light scattering, such as stimulated cathodoluminescence and streaking.Received 19 March 2021Accepted 7 June 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.L032036Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum coherence & coherence measuresQuantum controlQuantum-to-classical transitionUltrafast phenomenaPhysical SystemsRadiation from moving chargesAccelerators & BeamsGeneral PhysicsParticles & FieldsCondensed Matter, Materials & Applied Physics

Direct mapping of attosecond electron dynamics

The subcycle interaction of light and electrons has been one of the key frontiers in free-electron lasers, attosecond science and dynamical investigation of matter. Capturing the underlying subcycle dynamics of electrons with an optical field promises fascinating vistas with unprecedented temporal resolution. Yet the rigorous synchronization requirement has kept its realization out of reach. Here, by direct spatial observation of periodic electron bunch fringes, we demonstrate a laser streaking concept for revealing the dynamics of free electrons emitted from a plasma mirror under sub-relativistic laser intensity. Field-induced electron beam deflection demonstrates subcycle charge dynamics with a streaking speed of ~60 μrad as−1. This provides us with an attosecond-resolution metrology to obtain more direct evidence about the light-field-induced electron dynamics in the plasma mirror. Our results offer unprecedented characterization of attosecond dynamics and open the way to extensive experimental investigations of the interaction of attosecond electrons with intense lasers. By focusing a sub-relativistic infrared laser pulse onto a silica target, a periodic deflection pattern of attosecond electron pulse trains is observed. It reveals these subcycle charge dynamics with a streaking speed of ~60 μrad as−1.

Microscopy and diffraction with attosecond electron pulse trains

Attosecond imaging with electron beams can access optical-field-driven electron dynamics in space and time. Here we report first diffraction and microscopy experiments with attosecond electron pulses. We study attosecond-level timing of Bragg-spot emission and visualize light-wave propagation in space and time.

Generation and attosecond shaping of high coherence free-electron beams for ultrafast TEM

We demonstrate the generation and optical control of ultrashort high-coherence electron pulses. The free-electron quantum state is phase-modulated in the longitudinal and transverse dimensions, and the formation of attosecond electron pulse trains is quantitatively probed.

Attosecond electron pulse trains and quantum state reconstruction in ultrafast transmission electron microscopy

We introduce a framework for the preparation, coherent manipulation and characterization of free-electron quantum states, experimentally demonstrating attosecond pulse trains for electron microscopy. Specifically, we employ phase-locked single-color and two-color optical fields to coherently control the electron wave function along the beam direction. We establish a new variant of quantum state tomography - "SQUIRRELS" - to reconstruct the density matrices of free-electron ensembles and their attosecond temporal structure. The ability to tailor and quantitatively map electron quantum states will promote the nanoscale study of electron-matter entanglement and the development of new forms of ultrafast electron microscopy and spectroscopy down to the attosecond regime.

Diffraction and microscopy with attosecond electron pulse trains

Attosecond spectroscopy 1–7 can resolve electronic processes directly in time, but a movie-like space–time recording is impeded by the too long wavelength (~100 times larger than atomic distances) or the source–sample entanglement in re-collision techniques 8–11 . Here we advance attosecond metrology to picometre wavelength and sub-atomic resolution by using free-space electrons instead of higher-harmonic photons 1–7 or re-colliding wavepackets 8–11 . A beam of 70-keV electrons at 4.5-pm de Broglie wavelength is modulated by the electric field of laser cycles into a sequence of electron pulses with sub-optical-cycle duration. Time-resolved diffraction from crystalline silicon reveals a < 10-as delay of Bragg emission and demonstrates the possibility of analytic attosecond–angstrom diffraction. Real-space electron microscopy visualizes with sub-light-cycle resolution how an optical wave propagates in space and time. This unification of attosecond science with electron microscopy and diffraction enables space–time imaging of light-driven processes in the entire range of sample morphologies that electron microscopy can access. Attosecond light pulses are used to probe ultrafast processes. The experimental observation of attosecond electron pulses now promises the marriage of these techniques with electron microscopy and diffraction.

Production and characterization of attosecond electron bunch trains

We report the production of optically spaced attosecond electron microbunches produced by the inverse free-electron-laser (IFEL) process. The IFEL is driven by a Ti:sapphire laser synchronized with the electron beam. The IFEL is followed by a magnetic chicane that converts the energy modulation into the longitudinal microbunch structure. The microbunch train is characterized by observing coherent optical transition radiation (COTR) at multiple harmonics of the bunching. Experimental results are compared with 1D analytic theory showing good agreement. Estimates of the bunching factors are given and correspond to a microbunch length of 410 attosec FWHM. The formation of stable attosecond electron pulse trains marks an important step towards direct laser acceleration.