Generation of 100-MeV Attosecond Electron Bunches with Terawatt Few-Cycle Laser Pulses

Xing-Long Zhu, Wei-Yuan Liu, Min Chen, Su-Ming Weng, Feng He, Ralph Assmann, Zheng-Ming Sheng, and Jie Zhang

Phys. Rev. Applied 15, 044039 – Published 23 April 2021

Abstract

Laser-wakefield acceleration has been demonstrated to be a promising technique for compact electron accelerators. However, it is still challenging to achieve high-quality 100-MeV electron bunches of subfemtosecond duration with current techniques. Here, we present and numerically demonstrate an efficient scheme to produce such high-energy tunable ultrashort electron bunches, which is achieved by the use of a nonlinear wakefield driven by a terawatt few-cycle laser pulse in a tailored plasma channel. With the driving laser pulse energy of 25 mJ only, the resulting electron bunch can reach 101 MeV with 7.8-pC charge, approximately 4 mrad divergence, approximately 3% energy spread, energy efficiency above 3%, and a duration of hundreds of attoseconds. As such laser pulses may be obtained with a kilohertz repetition rate and high stability, our scheme could be interesting for ultrafast science and accelerator community.

Received 19 January 2021
Revised 1 April 2021
Accepted 2 April 2021

DOI:https://doi.org/10.1103/PhysRevApplied.15.044039

Physics Subject Headings (PhySH)

Electron beams & optics Laser driven electron acceleration Laser wakefield acceleration Laser-plasma interactions Particle acceleration in plasmas Ultrafast optics

Synchrotron radiation & free-electron lasers

Particle-in-cell methods

Accelerators & Beams

Authors & Affiliations

Xing-Long Zhu ^{1,2,3,4,*,‡}, Wei-Yuan Liu ^1,3,‡, Min Chen ^1,3, Su-Ming Weng ^1,3, Feng He^1,3, Ralph Assmann⁵, Zheng-Ming Sheng ^{1,2,3,4,6,†}, and Jie Zhang^1,3,7

¹Key Laboratory for Laser Plasmas (MOE), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
²SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG, United Kingdom
³Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
⁴Tsung-Dao Lee Institute, Shanghai 200240, China
⁵Deutsches Elektronen-Synchrotron DESY, D-22607 Hamburg, Germany
⁶Cockcroft Institute, Sci-Tech Daresbury, Cheshire WA4 4AD, United Kingdom
⁷Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

^*xinglong.zhu@sjtu.edu.cn
^†zmsheng@sjtu.edu.cn
^‡These authors contributed equally to this work.

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Vol. 15, Iss. 4 — April 2021

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Images

Figure 1
Schematic illustration. (a) A relativistic TW-class laser pulse propagates in a density-tailored plasma channel with three segments for injection, acceleration, and transportation, respectively. In the first segment, some plasma electrons at the rear of the first few buckets are trapped via the density gradient injection, and are then accelerated by the strong wakefield to high energies in the following accelerator segment. In the final conveyor segment, the accelerated electrons are transported from the plasma to the vacuum. (b)–(d) Illustration of 3D views of the TW laser-driven wakefield accelerator using 3D PIC simulations, which correspond to snapshots shown in Figs. 2–2 and more details are given correspondingly.
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Figure 2
(a) On-axis density distribution of the plasma channel. The color dots in (a) represent different positions shown in [(b), black dot], [(c), yellow dot], and [(d), green dot]. The plasma density $(n_{e})$ and the transverse laser field $(E_{y})$ in the upper graphs, the longitudinal wakefield $(E_{x})$ and its corresponding on-axis distribution in the lower graphs are shown at different positions $x = 90 λ_{0}$ (b), $180 λ_{0}$ (c), and $600 λ_{0}$ (d). The density and laser field are normalized to $n_{c}$ and $E_{0} = m_{e} c ω_{0} / e$ , respectively. (e) The trajectories of some typical electrons accelerated in the first bucket. (f) Snapshot of the electron bunches transported from the plasma to the vacuum.
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Figure 3
(a) Energy spectra of the accelerated electrons at different times. (b) The maximum energy $(E_{m})$ of the accelerated electrons and the ratio (defined as $ρ = E_{l} / E_{l 0}$ ) of the remaining laser pulse energy $(E_{l})$ to the initial pulse energy $(E_{l 0})$ , as a function of the interaction time t. The dashed curve in (b) indicates the fitting of electron energy as suggested by Eq. (2). The distributions of accelerated electrons in energy-longitudinal space (c) and energy angle (d).
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Figure 4
Energy efficiency $(η)$ , peak energy $(E_{e})$ , charge $(Q)$ , and beam duration $(t_{d})$ of the electrons accelerated in the first bucket as functions of (a) the length $L_{2}$ of the plasma density down ramp between the injector and accelerator, and (b) the density $n_{e 1}$ in the injection segment. The dashed lines in (a) and (b), respectively, indicate the $Q \propto 1 / L_{2}$ fitting and the $Q \propto n_{e 1}$ fitting for the total charge of the electrons injected in the first bucket. (c) Distributions of the plasma density and the transverse electric field for three cases with different initial laser phases $φ = 0$ (i), $π / 2$ (ii), and $π$ (iii) at the same position $x = 750 λ_{0}$ , where all other parameters are the same as those shown in Fig. 2.
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Figure 5
(a) Electron energy spectra at different times. The energy-space (b) and energy-angular (c) distributions of the electrons generated from a 10-mJ LWFA.
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