Time-of-flight electron energy loss spectroscopy using TM110 deflection cavities

Verhoeven, W.; Rens, J.F.M. van; Ninhuijs, M A W van; Toonen, W. F.; Kieft, ER Erik; Mutsaers, P.H.A.; Luiten, O.J.

doi:10.1063/1.4962698

Cited by 17 publications

(26 citation statements)

References 12 publications

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“…In contrast, isolated attosecond electron pulses will be required for studying cycle-irreversible dynamics (for example, long-lived electron correlations, heating, avalanche ionization and molecular dissociations), or processes that cannot be multi-cycle excited due to damage (for example, dielectric breakdown and extreme strong-field phenomena). The time-energy correlations that are created in the electron pulses with our concept might be useful for electron spectroscopy, for example via phase-space rotation 57,58 . Real-space attosecond microscopy can be invoked to image, for example, the oscillating electromagnetic fields 32 that cause the function of metamaterials or nanophotonic circuitry.…”

Section: Competing Interestsmentioning

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: Competing Interestsmentioning

confidence: 99%

Diffraction and microscopy with attosecond electron pulse trains

2017

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“…Because of the limitations of conventional techniques, time-of-flight (ToF) methods are emerging as an alternative, in which electron energies are derived from the flight time across a drift space. These methods put much less demands on the transverse beam quality, allowing for the detection of energy losses without requiring spatial filtering [17,18]. In this paper, we will demonstrate that ToF methods can be improved significantly to the level of state-of-the-art conventional methods by employing time-dependent electromagnetic fields to manipulate the longitudinal phase space distribution of an electron beam.…”

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confidence: 92%

“…This provides a large flexibility, allowing for the longitudinal phase space distribution to be optimized for each specific measurement. As with any method, the combination of resolutions achievable depends on the initial longitudinal emittance of the pulses.Experimental results.-In order to demonstrate the modified ToF detection scheme, a proof-of-principle measurement was performed by adapting the ToF setup previously reported in Ref [18]…”

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confidence: 99%

Time-of-flight electron energy loss spectroscopy by longitudinal phase space manipulation with microwave cavities

Verhoeven

Rens

Toonen

et al. 2018

Structural Dynamics

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The possibility to perform high-resolution time-resolved electron energy loss spectroscopy has the potential to impact a broad range of research fields. Resolving small energy losses with ultrashort electron pulses, however, is an enormous challenge due to the low average brightness of a pulsed beam. In this paper, we propose to use time-of-flight measurements combined with longitudinal phase space manipulation using resonant microwave cavities. This allows for both an accurate detection of energy losses with a high current throughput and efficient monochromation. First, a proof-of-principle experiment is presented, showing that with the incorporation of a compression cavity the flight time resolution can be improved significantly. Then, it is shown through simulations that by adding a cavity-based monochromation technique, a full-width-at-half-maximum energy resolution of 22 meV can be achieved with 3.1 ps pulses at a beam energy of 30 keV with currently available technology. By combining state-of-the-art energy resolutions with a pulsed electron beam, the technique proposed here opens up the way to detecting short-lived excitations within the regime of highly collective physics.

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“…The close relation between time and energy in femtosecond electron pulses offers another, dynamical approach for energy analysis 29 . The idea is to measure arrival time differences with femtosecond instead of nanosecond resolution.…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, smart phase-space shaping prior to temporal detection allows for substantial improvement of the energy resolution at cost of time resolution 30 . A first demonstration of such type of ultrafast time-of-flight analysis was made with a series of microwave cavities 29,30 that are synchronized to each other.…”

Section: Introductionmentioning

confidence: 99%

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

Ehberger

Kealhofer

Baum

2018

Structural Dynamics

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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.

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Time-of-flight electron energy loss spectroscopy using TM110 deflection cavities

Cited by 17 publications

References 12 publications

Diffraction and microscopy with attosecond electron pulse trains

Diffraction and microscopy with attosecond electron pulse trains

Time-of-flight electron energy loss spectroscopy by longitudinal phase space manipulation with microwave cavities

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

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