Production and characterization of attosecond electron bunch trains

Sears, Christopher M. S.; Colby, E.; Ischebeck, R.; McGuinness, C.; Nelson, J.; Noble, R.; Siemann, R.H.; Spencer, J.E.; Walz, D.; Plettner, T.; Byer, Robert L.

doi:10.1103/physrevstab.11.061301

Cited by 89 publications

(85 citation statements)

References 20 publications

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“…2c). This realspace streaking result directly demonstrates, in probably the clearest possible way, the presence of electron pulses with sub-optical-cycle localization in time 15,[18][19][20] . The duration of the laser-compressed electron pulses can be inferred from the streaked spot width divided by the streaking speed 13 , but numerically fitting the entire deflectogram to a model is more accurate.…”

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confidence: 99%

“…In this geometry (close to Brewster's angle), there is predominantly a periodic acceleration and deceleration of the electrons that is dependent on the arrival time at the membrane with respect to the laser cycles. Calculations predict [17][18][19] that such a periodic energy modulation 19 can reshape the incoming electron packet after some free-space propagation into a train of attosecond pulses 15,[18][19][20] (see Fig. 1).…”

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confidence: 99%

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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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Diffraction and microscopy with attosecond electron pulse trains

2017

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“…Demonstrations of practical structures that produce high gradient (690 MeV/m) [20] and staging demonstrations at 10 microns [21] and 0.8 microns [22] have begun to show the potential, but many issues remain to be addressed.…”

Section: Dielectric Laser Acceleration Randdmentioning

confidence: 99%

Roadmap to the Future

Colby

Len

2017

Reviews of Accelerator Science and Technology

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Most particle accelerators today are expensive devices found only in the largest laboratories, industries, and hospitals. Using techniques developed nearly a century ago, the limiting performance of these accelerators is often traceable to material limitations, power source capabilities, and the cost tolerance of the application. Advanced accelerator concepts a aim to increase the gradient of accelerators by orders of magnitude, using new power sources (e.g. lasers and relativistic beams) and new materials (e.g. dielectrics, metamaterials, and plasmas). Worldwide, research in this area has grown steadily in intensity since the 1980s, resulting in demonstrations of accelerating gradients that are orders of magnitude higher than for conventional techniques. While research is still in the early stages, these techniques have begun to demonstrate the potential to radically change accelerators, making them much more compact, and extending the reach of these tools of science into the angstrom and attosecond realms. Maturation of these techniques into robust, engineered devices will require sustained interdisciplinary, collaborative R&D and coherent use of test infrastructure worldwide. The outcome can potentially transform how accelerators are used.

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“…Novel schemes have been presented [9,10] as well as experimental demonstrations [11][12][13][14]. While the issue of generating optically-spaced electron microbunches is beyond the scope of this study, below we discuss a phenomenon common to all such schemes-beam loading.…”

Section: Introductionmentioning

confidence: 99%

“…In order to achieve net acceleration, several research groups are considering generation of optically-spaced electron microbunches [9][10][11][12][13][14]. Novel schemes have been presented [9,10] as well as experimental demonstrations [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Optimized operation of dielectric laser accelerators: Multibunch

Hanuka

Schächter

2018

Phys. Rev. Accel. Beams

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We present a self-consistent analysis to determine the optimal charge, gradient, and efficiency for laser driven accelerators operating with a train of microbunches. Specifically, we account for the beam loading reduction on the material occurring at the dielectric-vacuum interface. In the case of a train of microbunches, such beam loading effect could be detrimental due to energy spread, however this may be compensated by a tapered laser pulse. We ultimately propose an optimization procedure with an analytical solution for group velocity which equals to half the speed of light. This optimization results in a maximum efficiency 20% lower than the single bunch case, and a total accelerated charge of 10 6 electrons in the train. The approach holds promise for improving operations of dielectric laser accelerators and may have an impact on emerging laser accelerators driven by high-power optical lasers.

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Production and characterization of attosecond electron bunch trains

Cited by 89 publications

References 20 publications

Diffraction and microscopy with attosecond electron pulse trains

Diffraction and microscopy with attosecond electron pulse trains

Roadmap to the Future

Optimized operation of dielectric laser accelerators: Multibunch

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