The Development of Ultrafast Electron Microscopy

Aseyev, S. A.; Ryabov, E. A.; Миронов, Б. Н.; Ischenko, A. A.

doi:10.3390/cryst10060452

Cited by 25 publications

(16 citation statements)

References 63 publications

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“…The emergence of ultrafast transmission electron microscopy (UTEM) has added femtosecond (fs) temporal resolution to the suite of appealing capabilities of e-beams. − In this field, fs laser pulses are split into a component that irradiates a photocathode to generate individual fs electron pulses and another component that illuminates the sample with a well-controlled delay relative to the time of arrival of each electron pulse − (Figure b). Slow (sub-ps) structural changes produced by optical pumping have been tracked in this way, , while the optical-pump–electron-probe (OPEP) approach holds the additional potential to resolve ultrafast electron dynamics. , It should be noted that an alternative method in UTEM, consisting in blanking the e-beam with sub-ns precision, can be incorporated in high-end SEMs and TEMs without affecting the beam quality, although with smaller temporal precision than the photocathode-based technique.…”

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confidence: 99%

Optical Excitations with Electron Beams: Challenges and Opportunities

2021

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Free electron beams such as those employed in electron microscopes have evolved into powerful tools to investigate photonic nanostructures with an unrivaled combination of spatial and spectral precision through the analysis of electron energy losses and cathodoluminescence light emission. In combination with ultrafast optics, the emerging field of ultrafast electron microscopy utilizes synchronized femtosecond electron and light pulses that are aimed at the sampled structures, holding the promise to bring simultaneous sub-Å–sub-fs–sub-meV space–time–energy resolution to the study of material and optical-field dynamics. In addition, these advances enable the manipulation of the wave function of individual free electrons in unprecedented ways, opening sound prospects to probe and control quantum excitations at the nanoscale. Here, we provide an overview of photonics research based on free electrons, supplemented by original theoretical insights and discussion of several stimulating challenges and opportunities. In particular, we show that the excitation probability by a single electron is independent of its wave function, apart from a classical average over the transverse beam density profile, whereas the probability for two or more modulated electrons depends on their relative spatial arrangement, thus reflecting the quantum nature of their interactions. We derive first-principles analytical expressions that embody these results and have general validity for arbitrarily shaped electrons and any type of electron–sample interaction. We conclude with some perspectives on various exciting directions that include disruptive approaches to noninvasive spectroscopy and microscopy, the possibility of sampling the nonlinear optical response at the nanoscale, the manipulation of the density matrices associated with free electrons and optical sample modes, and appealing applications in optical modulation of electron beams, all of which could potentially revolutionize the use of free electrons in photonics.

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confidence: 99%

Optical Excitations with Electron Beams: Challenges and Opportunities

2021

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“…However, the propagation mechanism of the ultra-fast electron beam is very complicated due to the Coulomb force and the relativistic effect. Existing research shows that it is necessary to fulfill the ultra-high temporal and spatial resolution requirements to detect the materials' transient evolution [16]. Therefore, the longitudinal and transverse dimensions of the ultra-fast electron beam must be strictly controlled.…”

Section: Introductionmentioning

confidence: 99%

Control of the Longitudinal Compression and Transverse Focus of Ultrafast Electron Beam for Detecting the Transient Evolution of Materials

Cai

Wang

et al. 2022

Materials

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Ultrafast detection is an effective method to reveal the transient evolution mechanism of materials. Compared with ultra-fast X-ray diffraction (XRD), the ultra-fast electron beam is increasingly adopted because the larger scattering cross-section is less harmful to the sample. The keV single-shot ultra-fast electron imaging system has been widely used with its compact structure and easy integration. To achieve both the single pulse imaging and the ultra-high temporal resolution, magnetic lenses are typically used for transverse focus to increase signal strength, while radio frequency (RF) cavities are generally utilized for longitudinal compression to improve temporal resolution. However, the detection signal is relatively weak due to the Coulomb force between electrons. Moreover, the effect of RF compression on the transverse focus is usually ignored. We established a particle tracking model to simulate the electron pulse propagation based on the 1-D fluid equation and the 2-D mean-field equation. Under considering the relativity effect and Coulomb force, the impact of RF compression on the transverse focus was studied by solving the fifth-order Rung–Kutta equation. The results show that the RF cavity is not only a key component of longitudinal compression but also affects the transverse focusing. While the effect of transverse focus on longitudinal duration is negligible. By adjusting the position and compression strength of the RF cavity, the beam spot radius can be reduced from 100 μm to 30 μm under the simulation conditions in this paper. When the number of single pulse electrons remains constant, the electrons density incident on the sample could be increased from 3.18×1012 m−2 to 3.54×1013 m−2, which is 11 times the original. The larger the electron density incident on the sample, the greater the signal intensity, which is more conducive to detecting the transient evolution of the material.

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“…The manipulation of the longitudinal electron wavefunction component is also possible in ultrafast electron microscopes [65], where femtosecond electron pulses are produced from photocathodes illuminated by pulsed lasers, and the subsequent synchronized light-electron in- teraction allows one to inspect the specimen with femtosecond time resolution. This is the so-called photoninduced near-field electron microscopy [29, 30, 33-35, 66, 67] (PINEM), which, combined with free propagation, leads to attosecond electron compression [36,38,68,69] and endows the free electrons with the ability to transfer quantum coherence between different systems [70,71].…”

Section: Introductionmentioning

confidence: 99%