Laser streaking of free electrons at 25 keV

Kirchner, Friedrich O.; Gliserin, Alexander; Krausz, Ferenc; Baum, Peter

doi:10.1038/nphoton.2013.315

Cited by 140 publications

(163 citation statements)

References 42 publications

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“…The compressed electron pulses are therefore tilted with respect to their propagation direction, but this tilt is effectively compensated at the second foil, which is aligned in parallel to the first one by < 0.1°. If non-tilted electron pulses are needed, velocity matching can be applied 14 to produce equal timing differences of the optical phase front and the electron incidence along the entire membrane surface. The longitudinal length over which the electron pulses keep compressed (depth of focus) is hundreds of micrometres, which well covers the thickness of samples in electron diffraction or microscopy.…”

Section: Methodsmentioning

confidence: 99%

Diffraction and microscopy with attosecond electron pulse trains

2017

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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 techniques [8][9][10][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][9][10][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.Our concepts for generating attosecond electron pulses, direct streaking-oscilloscope characterization, atomic diffraction and proof-of-principle attosecond electron microscopy of electromagnetic fields are depicted in Fig. 1. A femtosecond laser 12 triggers electron emission from a photocathode (yellow) and produces electron pulses of ~1 ps duration at a central energy of E el = 70 keV (ref.13 ). The de Broglie wavelength is λ el ≈ 4.5 pm and spacecharge effects are avoided by using fewer than one electron per pulse at the sample. A first laser beam ('modulation') is used to compress the electron pulse into a sub-cycle pulse train. For this purpose, we let the laser beam and the electron beam intersect at a 50-nm-thick silicon nitride membrane that lets the electrons pass through. The membrane is also transparent to the laser beam (1,030 nm wavelength), but the refractive index of ~2 in combination with thin-layer interferences generates a phase shift between the incoming and outgoing electromagnetic waves. Therefore, the periodic electromagnetic acceleration and deceleration of the propagating electrons in the optical field cycles before and after the membrane do not cancel out after passage through the laser focus, as would happen in free space 13 . In the end, there remains a time-dependent overall momentum kick that is proportional to the change of vector potential at the membrane and therefore dependent on the optical phase. In contrast to metal foils 13,14 , graphite 15 or nanostructures 16 , a dielectric membrane has negligible linear or nonlinear optical absorption and can therefore sustain an extreme level of power and fields, enabling strong/effective compression and metrology.In the experiment, we let the electron beam (0.48 × speed of light) and the laser beam (p-polarized, ~15 mW, peak field ~5 × 10 7 V m -1 ) hit the membrane under 35° and 60° from the surface...

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Section: Methodsmentioning

confidence: 99%

Diffraction and microscopy with attosecond electron pulse trains

2017

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“…1). The development of PINEM enables the visualization of the spatiotemporal dielectric response of nanostructures (9), visualization of plasmonic fields (4,5) and their spatial interferences (10), imaging of low atomic number nanoscale materials (11), characterization of ultrashort electron packets (12,13), and imaging of different biological structures (14).…”

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confidence: 99%

Photon gating in four-dimensional ultrafast electron microscopy

Hassan

Liu

Baskin

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Ultrafast electron microscopy (UEM) is a pivotal tool for imaging of nanoscale structural dynamics with subparticle resolution on the time scale of atomic motion. Photon-induced near-field electron microscopy (PINEM), a key UEM technique, involves the detection of electrons that have gained energy from a femtosecond optical pulse via photon-electron coupling on nanostructures. PINEM has been applied in various fields of study, from materials science to biological imaging, exploiting the unique spatial, energy, and temporal characteristics of the PINEM electrons gained by interaction with a "single" light pulse. The further potential of photon-gated PINEM electrons in probing ultrafast dynamics of matter and the optical gating of electrons by invoking a "second" optical pulse has previously been proposed and examined theoretically in our group.Here, we experimentally demonstrate this photon-gating technique, and, through diffraction, visualize the phase transition dynamics in vanadium dioxide nanoparticles. With optical gating of PINEM electrons, imaging temporal resolution was improved by a factor of 3 or better, being limited only by the optical pulse widths. This work enables the combination of the high spatial resolution of electron microscopy and the ultrafast temporal response of the optical pulses, which provides a promising approach to attain the resolution of few femtoseconds and attoseconds in UEM.photon-induced near-field electron microscopy | attosecond electron microscopy | optical-gated electron pulse | time-resolved PINEM | photon-electron gating I n ultrafast electron microscopy (UEM) (1-3), electrons generated by photoemission at the cathode of a transmission electron microscope are accelerated down the microscope column to probe the dynamic evolution of a specimen initiated by an ultrafast light pulse. The use of femtosecond lasers to generate the electron probe and excite the specimen has made it possible to achieve temporal resolution on the femtosecond time scale, as determined by the cross-correlation of the optical and electron pulses. One important method in the UEM repertoire is photon-induced near-field electron microscopy (PINEM) (4, 5), in which the dynamic response detected by the electron probe is the pump-induced charge density redistribution in nanoscale specimens (6).Photon-electron coupling is the basic building block of PINEM, which takes place in the presence of nanostructures when the energy-momentum conservation condition is satisfied (4, 5). This coupling leads to inelastic gain/loss of photon quanta by electrons in the electron packet, which can be resolved in the electron energy spectrum (5,7,8). This spectrum consists of discrete peaks, spectrally separated by multiples of the photon energy (nZω), on the higher and lower energy sides of the zero loss peak (ZLP) (4) (Fig. 1). The development of PINEM enables the visualization of the spatiotemporal dielectric response of nanostructures (9), visualization of plasmonic fields (4, 5) and their spatial interferences (10), imag...

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“…A temporal pulse characterization by ultrafast streaking [205][206][207][208]. The electron pulses are channeled through a narrow and rapidly changing electromagnetic field normal to their propagation direction.…”

Section: Alternative Approaches To Determine the Pulse Durationmentioning

confidence: 99%

“…Recently, so called laser streaking has been developed, which is based on the electron probe and laser pump beam being intersected at an ultrathin metal mirror. This concept potentially allows for sub-femtosecond temporal resolution, since it mainly depends on the duration of the employed laser pulses [208]. For high energy electron pulses, this method bears large potential for an extremely precise temporal characterization.…”

Section: Alternative Approaches To Determine the Pulse Durationmentioning

confidence: 99%

Development of an Ultrafast Low-Energy Electron Diffraction Setup

Gulde

2015

Springer Theses

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Laser streaking of free electrons at 25 keV

Cited by 140 publications

References 42 publications

Diffraction and microscopy with attosecond electron pulse trains

Diffraction and microscopy with attosecond electron pulse trains

Photon gating in four-dimensional ultrafast electron microscopy

Development of an Ultrafast Low-Energy Electron Diffraction Setup

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