Direct Visualization of Light-Driven Atomic-Scale Carrier Dynamics in Space and Time DIVI

Institutions
  • WG Baum (Experimentalphysik mit SP Photonik)
Publications
    Ehberger, Dominik; Mohler, Kathrin J.; Vasileiadis, Thomas; Ernstorfer, Ralph; Waldecker, Lutz; Baum, Peter (2019): Terahertz Compression of Electron Pulses at a Planar Mirror Membrane Physical Review Applied. 2019, 11(2), 024034. eISSN 2331-7019. Available under: doi: 10.1103/PhysRevApplied.11.024034

Terahertz Compression of Electron Pulses at a Planar Mirror Membrane

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Compression of electron pulses with terahertz radiation offers short pulse durations and intrinsic subcycle stability in time. We report the generation of 12-fs (rms), 28-fs (FWHM) electron pulses at a kinetic energy of 75 keV by using single-cycle terahertz radiation and a simple planar mirror. The mirror interface provides transverse velocity matching and spatially uniform compression in time with purely longitudinal field-electron interaction. The measured short-term and long-term temporal drifts are substantially below the pulse duration without any active synchronization. A simple phase-space model explains the measured temporal focusing dynamics for different compressor strengths and shows a path toward generating isolated attosecond electron pulses from beams of almost arbitrary transverse emittance.

Origin (projects)

    Ehberger, Dominik; Ryabov, Andrey; Baum, Peter (2018): Tilted Electron Pulses Physical Review Letters. 2018, 121(9), 094801. ISSN 0031-9007. eISSN 1079-7114. Available under: doi: 10.1103/PhysRevLett.121.094801

Tilted Electron Pulses

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We report the all-optical generation and characterization of tilted electron pulses by means of single-cycle terahertz radiation at an electron-transmitting mirror at slanted orientation. Femtosecond electron pulses with a chosen tilt angle are produced at an almost arbitrary target location. The experiments along with theory further reveal that the pulse front tilt in electron optics is directly connected to angular dispersion. Quantum mechanical considerations suggest that this relation is general for particle beams at any degree of coherence. These results indicate that ultrashort electron pulses can be shaped in space and time as versatilely as femtosecond laser pulses, but at 105 times finer wavelength and subnanometer imaging resolution.

Origin (projects)

    Ehberger, Dominik; Kealhofer, Catherine; Baum, Peter (2018): Electron energy analysis by phase-space shaping with THz field cycles Structural dynamics. 2018, 5(4), 044303. ISSN 2329-7778. eISSN 2329-7778. Available under: doi: 10.1063/1.5045167

Electron energy analysis by phase-space shaping with THz field cycles

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Time-resolved electron energy analysis and loss spectroscopy can reveal a wealth of information about material properties and dynamical light-matter interactions. Here, we report an all-optical concept for measuring energy spectra of femtosecond electron pulses with sub-eV resolution. Laser-generated terahertz radiation is used to measure arrival time differences within electron pulses with few-femtosecond precision. Controlled dispersion and subsequent compression of the electron pulses provide almost any desired compromise of energy resolution, signal strength, and time resolution. A proof-of-concept experiment on aluminum reveals an energy resolution of <3.5 eV (rms) at 70-keV after a drift distance of only 0.5 m. Simulations of a two-stage scheme reveal that pre-stretched pulses can be used to achieve <10 meV resolution, independent of the source's initial energy spread and limited only by the achievable THz field strength and measuring time.

Origin (projects)

    Tsarev, Maxim V.; Baum, Peter (2018): Characterization of non-relativistic attosecond electron pulses by transition radiation from tilted surfaces New Journal of Physics. 2018, 20(3), 033002. eISSN 1367-2630. Available under: doi: 10.1088/1367-2630/aaad94

Characterization of non-relativistic attosecond electron pulses by transition radiation from tilted surfaces

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We consider analytically and numerically the emission of coherent transition radiation by few-femtosecond and attosecond electron pulses. With optimized geometries based on tilted surfaces we avoid the influences of the beam diameter and velocity mismatch for sub-relativistic pulses. We predict the emission of visible and ultraviolet optical radiation that characterizes few-femtosecond or attosecond electron pulses in time. The total amount of radiation depends on the source' repetition rate and number of electrons per macro/microbunch and is in many cases sufficient for pulse length characterization in the emerging experiments.

Origin (projects)

    Morimoto, Yuya; Baum, Peter (2018): Diffraction and microscopy with attosecond electron pulse trains Nature Physics. 2018, 14(3), pp. 252-256. ISSN 1745-2473. eISSN 1745-2481. Available under: doi: 10.1038/s41567-017-0007-6

Diffraction and microscopy with attosecond electron pulse trains

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Attosecond spectroscopy1–7 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 techniques8–11. Here we advance attosecond metrology to picometre wavelength and sub-atomic resolution by using free-space electrons instead of higher-harmonic photons1–7 or re-colliding wavepackets8–11. 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–ångström 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.

Origin (projects)

  Morimoto, Yuya; Baum, Peter (2018): Attosecond control of electron beams at dielectric and absorbing membranes Physical Review A. 2018, 97(3), 033815. ISSN 1050-2947. eISSN 2469-9934. Available under: doi: 10.1103/PhysRevA.97.033815

Attosecond control of electron beams at dielectric and absorbing membranes

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Ultrashort electron pulses are crucial for time-resolved electron diffraction and microscopy of fundamental light-matter interaction. In this work, we study experimentally and theoretically the generation and characterization of attosecond electron pulses by optical-field-driven compression and streaking at dielectric or absorbing interaction elements. The achievable acceleration and deflection gradient depends on the laser-electron angle, the laser's electric and magnetic field directions and the foil orientation. Electric and magnetic fields have similar contributions to the final effect and both need to be considered. Experiments and theory agree well and reveal the optimum conditions for highly efficient, velocity-matched electron-field interactions in longitudinal or transverse direction. We find that metallic membranes are optimum for light-electron control at mid-infrared or terahertz wavelengths, but dielectric membranes are excel in the visible/near-infrared regimes and are therefore ideal for the formation of attosecond electron pulses.

Origin (projects)

    Ryabov, Andrey; Baum, Peter (2016): Electron microscopy of electromagnetic waveforms Science. 2016, 353(6297), pp. 374-377. ISSN 0036-8075. eISSN 1095-9203. Available under: doi: 10.1126/science.aaf8589

Electron microscopy of electromagnetic waveforms

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Rapidly changing electromagnetic fields are the basis of almost any photonic or electronic device operation. We report how electron microscopy can measure collective carrier motion and fields with subcycle and subwavelength resolution. A collimated beam of femtosecond electron pulses passes through a metamaterial resonator that is previously excited with a single-cycle electromagnetic pulse. If the probing electrons are shorter in duration than half a field cycle, then time-frozen Lorentz forces distort the images quasi-classically and with subcycle time resolution. A pump-probe sequence reveals in a movie the sample's oscillating electromagnetic field vectors with time, phase, amplitude, and polarization information. This waveform electron microscopy can be used to visualize electrodynamic phenomena in devices as small and fast as available.

Origin (projects)

    Yang, Ding-Shyue; Baum, Peter; Zewail, Ahmed H. (2016): Ultrafast electron crystallography of the cooperative reaction path in vanadium dioxide Structural dynamics. 2016, 3(3), pp. 034304. eISSN 2329-7778. Available under: doi: 10.1063/1.4953370

Ultrafast electron crystallography of the cooperative reaction path in vanadium dioxide

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Time-resolved electron diffraction with atomic-scale spatial and temporal resolution was used to unravel the transformation pathway in the photoinduced structural phase transition of vanadium dioxide. Results from bulk crystals and single-crystalline thin-films reveal a common, stepwise mechanism: First, there is a femtosecond V-V bond dilation within 300 fs, second, an intracell adjustment in picoseconds and, third, a nanoscale shear motion within tens of picoseconds. Experiments at different ambient temperatures and pump laser fluences reveal a temperature-dependent excitation threshold required to trigger the transitional reaction path of the atomic motions.

Origin (projects)

    Kealhofer, Catherine; Schneider, Waldemar; Ehberger, Dominik; Ryabov, Andrey; Krausz, Ferenc; Baum, Peter (2016): All-optical control and metrology of electron pulses Science. 2016, 352(6284), pp. 429-433. ISSN 0036-8075. eISSN 1095-9203. Available under: doi: 10.1126/science.aae0003

All-optical control and metrology of electron pulses

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Short electron pulses are central to time-resolved atomic-scale diffraction and electron microscopy, streak cameras, and free-electron lasers. We demonstrate phase-space control and characterization of 5-picometer electron pulses using few-cycle terahertz radiation, extending concepts of microwave electron pulse compression and streaking to terahertz frequencies. Optical-field control of electron pulses provides synchronism to laser pulses and offers a temporal resolution that is ultimately limited by the rise-time of the optical fields applied. We used few-cycle waveforms carried at 0.3 terahertz to compress electron pulses by a factor of 12 with a timing stability of <4 femtoseconds (root mean square) and measure them by means of field-induced beam deflection (streaking). Scaling the concept toward multiterahertz control fields holds promise for approaching the electronic time scale in time-resolved electron diffraction and microscopy.

Origin (projects)

    Gliserin, Alexander; Walbran, Matthew; Krausz, Ferenc; Baum, Peter (2015): Sub-phonon-period compression of electron pulses for atomic diffraction Nature communications. 2015, 6, 8723. eISSN 2041-1723. Available under: doi: 10.1038/ncomms9723

Sub-phonon-period compression of electron pulses for atomic diffraction

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Visualizing the rearrangement of atoms in a wide range of molecular and condensed-matter systems requires resolving picometre displacements on a 10-fs timescale, which is achievable using pump-probe diffraction, given short enough pulses. Here we demonstrate the compression of single-electron pulses with a de Broglie wavelength of 0.08 ångström to a full-width at half-maximum duration of 28 fs or equivalently 12-fs root-mean square, substantially shorter than most phonon periods and molecular normal modes. Atomic resolution diffraction from a complex organic molecule is obtained with good signal-to-noise ratio within a data acquisition period of minutes. The electron-laser timing is found to be stable within 5 fs (s.d.) over several hours, allowing pump-probe diffraction at repetitive excitation. These measurements show the feasibility of laser-pump/electron-probe scans that can resolve the fastest atomic motions relevant in reversible condensed-matter transformations and organic chemistry.

Origin (projects)

    Yakovlev, Vladislav S.; Stockman, Mark I.; Krausz, Ferenc; Baum, Peter (2015): Atomic-scale diffractive imaging of sub-cycle electron dynamics in condensed matter Scientific reports. 2015, 5, 14581. eISSN 2045-2322. Available under: doi: 10.1038/srep14581

Atomic-scale diffractive imaging of sub-cycle electron dynamics in condensed matter

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For interaction of light with condensed-matter systems, we show with simulations that ultrafast electron and X-ray diffraction can provide a time-dependent record of charge-density maps with sub-cycle and atomic-scale resolutions. Using graphene as an example material, we predict that diffraction can reveal localised atomic-scale origins of optical and electronic phenomena. In particular, we point out nontrivial relations between microscopic electric current and density in undoped graphene.

Origin (projects)

    Kasmi, Lamia; Kreier, Daniel; Bradler, Maximilian; Riedle, Eberhard; Baum, Peter (2015): Femtosecond single-electron pulses generated by two-photon photoemission close to the work function New Journal of Physics. 2015, 17(3), 033008. eISSN 1367-2630. Available under: doi: 10.1088/1367-2630/17/3/033008

Femtosecond single-electron pulses generated by two-photon photoemission close to the work function

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dc.title:


dc.contributor.author: Kasmi, Lamia; Kreier, Daniel; Bradler, Maximilian; Riedle, Eberhard; Baum, Peter

Origin (projects)

Funding sources
Name Finanzierungstyp Kategorie Project no.
Europäische Union third-party funds research funding program 748/18
Further information
Period: 01.05.2018 – 31.07.2020