Detecting Electron Motion in Atoms and Molecules

Shao, Hua‐Chieh; Starace, Anthony F.

doi:10.1103/physrevlett.105.263201

Cited by 97 publications

(92 citation statements)

References 22 publications

(34 reference statements)

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“…Bragg spot intensity is related to the scattering potential via the structure factor and a time-resolved recording of Bragg spots from a material under laser excitation can therefore reveal time-dependent charge-density maps [23][24][25][26] . Here we estimate the magnitude of Bragg intensity changes originating from atomic-scale electronic motion in silicon.…”

Section: Streaking Deflectogram Simulation the Deflectogram D(x δ T)mentioning

confidence: 99%

“…Figure 3c shows that the overall intensity of the Bragg spots (that is, the structure factor representing the scattering potential within the unit cell) does not change beyond the experimental shot-noise limit when activating the compression. Diffractive imaging of laser-driven electronic motion in molecules or condensed matter requires percentage-level sensitivities to intensity changes [23][24][25][26] , a signal-to-noise ratio that our attosecond electron pulses can provide (see Fig. 3c), even although our electron source was operated far from optimum conditions (see Methods).…”

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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: Streaking Deflectogram Simulation the Deflectogram D(x δ T)mentioning

confidence: 99%

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confidence: 99%

Diffraction and microscopy with attosecond electron pulse trains

2017

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“…The methods of ultrafast electron crystallography and electron microscopy with temporal resolution from micro-to subpicoseconds provide great opportunities to the study of the 4D structural dynamics (see the review articles [21,54] and the monograph [2]). Very recent advances in the formation of ultrashort electron pulses allow us to reach an attosecond temporal resolution and observe the coherent dynamics of the electrons in molecules [55][56][57].…”

Section: Discussionmentioning

confidence: 99%

Ultrafast Electron Microscopy for Chemistry, Biology and Material Science

Aseyev¹,

Weber²,

Ischenko³

2013

JASMI

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For the past thirty years, intense efforts have been made to record atomic scale movies that reveal the movement of atoms in molecules, the fast dynamical processes in biological tissues and cells, and the changes in the structure of a solid confined to nano-scale volumes. A combination of sub-nanometer spatial resolution with picosecond or even femtosecond temporal resolution is required for such atomic movies. Additional important information can be obtained when the energy of the electron beam transmitted through the sample is measured. The four dimensional (4D) spatially and temporally resolved ultrafast electron microscopy method is made possible by the extremely high detection efficiency that is reached in 4D electron microscopy. Using ultra-short electron bunches for the visualization of biological tissue can also improve the spatial resolution compared to conventional electron microscopes, thereby enabling the study of complex biological samples of relevance to the life sciences. Of particular interest to a broad audience is the possibility to create a video, and in the future, a real atomic movie, using 4D electron tomography. IntroductionSince the 1980s, intense efforts have been made to record an atomic movie showing the movements of atoms within molecules, the fast dynamical processes in biological tissues and cells, and the changes in the structure of a solid in a nano-scale volume [1][2][3]. Such an atomic movie requires a combination of sub-nanometer spatial resolution with picosecond or even femtosecond temporal resolution. The aim of any microscopy is to study the structure, composition, and a variety of physical and chemical characteristics of samples (usually solids) on a very small length scale, with linear dimensions of irregularities that are on the order of micrometers or nanometers. While in most microscopies, photon beams (in optical microscopy) or corpusclar beams (for example in electron microscopy) are used as the probes, tunneling microscopies use a very sharp tip that is scanned across surfaces. Electron microscopy and optical microscopy use light and a focused electron beam for imaging, respectively. Beyond those, other microscopic methods may use ions, protons, positrons, or neutrons, or acoustic or microwave radiation in addition to other, less common, methods [3][4][5][6]. In each of them, the specificity of the interaction of a beam of the particles (or photons) and the molecules or atoms of a sample yield unique and rather useful information about the structure, composition and microscopic inhomogeneities of the sample, and the nature of their intermolecular interactions [3,4,7]. For example, the slow neutrons in neutron microscopy and spectroscopy barely interact with the electrons, but interact strongly with the nuclei of the atoms.There are two main approaches to achieve imaging in classical microscopy: 1) In transmission mode, a large area of the sample is illuminated by a beam of light or particles. Specifically designed lenses project the transmitted beam onto a...

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“…Nevertheless, nowadays sub-100-fs electron pulses have been produced [6], and various schemes to generate attosecond electron pulses have been proposed [7][8][9][10]. Simulations have demonstrated the abilities of attosecond electron pulses to directly image electronic motions in atoms and molecules [11][12][13][14][15].…”

Section: Introductionmentioning

confidence: 99%

Imaging electronic motions in atoms by energy-resolved ultrafast electron diffraction

Shao¹,

Starace²

2014

Phys. Rev. A

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We propose energy-resolved ultrafast electron diffraction as a means of directly imaging target electronic motions whose space, time, and energy information can be simultaneously retrieved from time-resolved diffraction measurements. The energy-resolved diffraction images are simulated for breathing, wiggling, and hybrid modes of electronic motion in the H atom. The simulations demonstrate the capabilities of ultrafast electron diffraction to image and distinguish different kinds of electronic motion. The theoretical analysis of the scattering process identifies the requirements for time-and state-resolved imaging of electronic motion and provides interpretations of the results.

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Detecting Electron Motion in Atoms and Molecules

Cited by 97 publications

References 22 publications

Diffraction and microscopy with attosecond electron pulse trains

Diffraction and microscopy with attosecond electron pulse trains

Ultrafast Electron Microscopy for Chemistry, Biology and Material Science

Imaging electronic motions in atoms by energy-resolved ultrafast electron diffraction

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