Attosecond electron bunch measurement with coherent nonlinear Thomson scattering

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Attosecond electron bunch measurement with coherent nonlinear Thomson scattering

Colton Fruhling, Grigory Golovin, and Donald Umstadter

Phys. Rev. Accel. Beams 23, 072802 – Published 6 July 2020

Abstract

We present a novel method for measurement of ultrashort electron-bunch duration, in principle, as short as zeptosecond ( $10^{- 21} s$ ). The method employs nonlinear Thomson scattering of relativistically intense laser light, and takes advantage of the nonlinear dependence and coherence of scattered light on electron bunch length. We validate the method and test its range of applicability via simulations by using realistic (nonideal) electron beams. Due to the wide flexibility in choice of interaction geometry and scattering laser pulse properties enabled by the method, it is shown to be applicable over a wide range of electron beam parameters, including energy, energy spread, and divergence angle.

Received 3 March 2020
Accepted 5 June 2020

DOI:https://doi.org/10.1103/PhysRevAccelBeams.23.072802

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Beam diagnostics Light-matter interaction

Laser applications

Accelerators & Beams

Authors & Affiliations

Colton Fruhling ^*, Grigory Golovin, and Donald Umstadter

Department of Physics and Astronomy, University of Nebraska-Lincoln, Behlen Laboratory 500 Stadium Drive, Nebraska 68588, USA

^*colton.fruhling@huskers.unl.edu

Article Text

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Issue

Vol. 23, Iss. 7 — July 2020

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Images

Figure 1
The minimum bunch duration measurement possible based on ideal detection for SPR (diagonal hatched), CTR (horizontally hatched), and NTS for $a_{0} = 4$ (vertically hatched) and $a_{0} = 20$ (shaded) under typical experimental conditions. The dimensionless laser intensity parameter, $a_{0}$ , is defined later in the text. The shading indicates applicability that extends to the top right. SPR [12, 22] is considered in the case where the distance of the beam from the grating is $d = 1 mm$ . CTR [14, 23] is considered in the case where aluminum, a common material, is used for a transition material. NTS is considered with the parameters used in this paper, $a_{0} = 4$ , and at state-of-the-art systems where $a_{0} = 20$ .
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Figure 2
A schematic of the electron pulse measurement concept. An intense laser pulse (red) interacts with a relativistically moving electron bunch (blue). The interaction angle $\cos θ_{int} = ⟨ {\vec{β}}_{0} ⟩ \cdot \hat{k}$ is defined by the angle between the incoming laser pulse and the average electron bunch direction of motion, which is defined to be along the positive z axis. The radiation emitted is shown below the interaction and is composed of many different frequencies, which are coherent or incoherent based on whether the relation $ω λ_{e} / 2 π c$ is less than or greater than 1. From the spectrum, which displays the change from coherent to incoherent, one can reconstruct the bunch length.
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Figure 3
Simulation results for the ideal and realistic beam conditions. The laser intensity is $a_{0} = 4$ , spot size $25 μ m$ . The electron energy is $γ = 10$ . (a) The NTS radiation spectra for a single electron, ideal, and realistic electron beams. (b) Form factors $F (ω)$ . The analysis region is shown between the vertical dashed lines. (b) The reconstructed bunch profiles and their comparison to the simulation input.
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Figure 4
Simulation results for the ideal beam conditions. The laser intensity is $a_{0} = 4$ , spot size $25 μ m$ . The electron energy is $γ = 10$ . The beam size is 4.5, 9, and 18 nm respectively. The spectrum is shown for each case as well as a dashed, dotted, and dot-dashed vertical line at first minimum of the spectrum for each case respectively.
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Figure 5
The radiation for a single electron and a bunch of 5000 are plotted on the left. As can be seen the single electron spectrum is a poor representation for the many electron case and a calculation using knowledge of the input electron energy spectrum is used instead and shown in green. The green curve is used as an incoherent signal to find the form factor, shown in the middle in log-log scale. The Gaussian fit is shown in red and the bounds of fitting are dashed vertical lines. The reconstruction, on the right, recovers the bunch length with good fidelity.
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