Transient Relativistic Plasma Grating to Tailor High-Power Laser Fields, Wakefield Plasma Waves, and Electron Injection

Qiang Chen, Dominika Maslarova, Junzhi Wang, Shao Xian Lee, Vojtech Horný, and Donald Umstadter

Phys. Rev. Lett. 128, 164801 – Published 20 April 2022

Abstract

We show the first experiment of a transverse laser interference for electron injection into the laser plasma accelerators. Simulations show such an injection is different from previous methods, as electrons are trapped into later acceleration buckets other than the leading ones. With optimal plasma tapering, the dephasing limit of such unprecedented electron beams could be potentially increased by an order of magnitude. In simulations, the interference drives a relativistic plasma grating, which triggers the splitting of relativistic-intensity laser pulses and wakefield. Consequently, spatially dual electron beams are accelerated, as also confirmed by the experiment.

Received 12 July 2021
Revised 20 January 2022
Accepted 21 March 2022

DOI:https://doi.org/10.1103/PhysRevLett.128.164801

Physics Subject Headings (PhySH)

Beam injection, extraction & transport High intensity laser-plasma interactions Laser driven electron acceleration Laser wakefield acceleration Photonic crystals Ultrafast optics Ultrafast phenomena

Accelerators & BeamsAtomic, Molecular & OpticalPlasma PhysicsNonlinear Dynamics

Authors & Affiliations

Qiang Chen ¹, Dominika Maslarova ^2,3, Junzhi Wang ¹, Shao Xian Lee¹, Vojtech Horný ^4,5, and Donald Umstadter ^1,*

¹Extreme Light Laboratory, Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
²Institute of Plasma Physics of the Czech Academy of Sciences, Za Slovankou 1782/3, 182 00 Prague, Czech Republic
³Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Břehová 78/7, 115 19 Prague, Czech Republic
⁴Department of Physics, Chalmers University of Technology, Fysikgarden 1, 412 58 Gothenburg, Sweden
⁵LULI-CNRS, École Polytechnique, CEA: Université Paris-Saclay; UPMC Univ Paris 06: Sorbonne Universités, F-91128 Palaiseau Cedex, France

^*donald.umstadter@unl.edu

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Issue

Vol. 128, Iss. 16 — 22 April 2022

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Images

Figure 1
Experiment setup for the electron injection and acceleration. The left-bottom inset illustrates, from the top view, the formation of the interference with a wavelength $λ_{I} = λ_{0} / [2 \sin (θ / 2)] = 4.6 μ m$ .
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Figure 2
Electron beam injection and trapping process. (a) Experiment: spatial profile of the electron beam measured in the direction of laser beam 1, with an average plasma density $n_{e} \approx 5 \times 10^{18} {cm}^{- 3}$ corresponding to full gas ionization. (b) Experiment: electron beam spectrum of (a). (c)–(e) Simulation: electron density profile in the simulation time of 0.6 ps [(c) laser-laser overlap], 1.13 ps [(d) wakefield recovering], and 1.67 ps [(e) electron trapping]. One beam arrived at the intersection at $t_{d 1} = 0$ , while the other delayed one arrived at $t_{d 2} = 0.5 τ$ . Black dots correspond to electron macroparticles that were injected.
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Figure 3
Energy evolution of plasma electrons during the injection process shown in Fig. 2. The dashed lines show the times of the largest overlap of the laser beams and the time when the laser beams transversely separate by $w_{0}$ at the simulation times of 0.6 and 0.82 ps, respectively. The inset shows further energy evolution [until Fig. 2 stage]; the dotted rectangle part corresponds to the main figure.
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Figure 4
Dependence of electron injection on pulse delay. (a) Experiment: charge of the optically injected electron beam(s) $Q_{1, 2}$ , their statistical medians, and median absolute deviation, in either laser pulse direction, as a function of delay $τ_{d}$ , with units in the pulse duration $τ_{0} = 35 fs$ . Positive $τ_{d}$ means pulse 2 ahead and negative for pulse 1 ahead. (b) Simulation: delay scan with units in the pulse duration $τ = 29 fs$ to see changes in the injected charge per length $Q_{2}$ (red, considering electrons whose energy reached $\geq 15 MeV$ in the time of 2.70 ps), the maximum wakefield amplitude $A_{w}$ (black, for recovered wakefields at 1.49 ps), and the maximum interference intensity $A_{i}$ (blue).
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Figure 5
Nearly parallel electron beams simultaneously accelerated by a modulated wakefield. (a) Simulation: electron density profile showing wakefield splitting $Δ x \approx 510 μ m$ after the injection process depicted in Fig. 2. Black dots represent examples of trapped electron macroparticles. The inset shows the corresponding modulated laser intensity profile (in arb. units). (b),(c) Experiment: electron spatial profile showing dual electron beams split along different directions.
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