Model-independent inference of laser intensity

Open Access

Model-independent inference of laser intensity

T. G. Blackburn, E. Gerstmayr, S. P. D. Mangles, and M. Marklund

Phys. Rev. Accel. Beams 23, 064001 – Published 11 June 2020

Abstract

An ultrarelativistic electron beam passing through an intense laser pulse emits radiation around its direction of propagation into a characteristic angular profile. Here, we show that measurement of the variances of this profile in the planes parallel and perpendicular to the laser polarization, and the mean initial and final energies of the electron beam, allows the intensity of the laser pulse to be inferred in a way that is independent of the model of the electron dynamics. The method presented applies whether radiation reaction is important or not, and whether it is classical or quantum in nature, with an accuracy of a few percent across 3 orders of magnitude in intensity. It is tolerant of electron beams with a broad energy spread and finite divergence. In laser-electron-beam collision experiments, where spatiotemporal fluctuations cause the alignment of the beams to vary from shot to shot, this permits inference of the laser intensity at the collision point, thereby facilitating comparisons between theoretical calculations and experimental data.

Received 6 November 2019
Accepted 13 May 2020

DOI:https://doi.org/10.1103/PhysRevAccelBeams.23.064001

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. Funded by Bibsam.

Published by the American Physical Society

Physics Subject Headings (PhySH)

High intensity laser-plasma interactions

Radiation from moving charges

Accelerators & Beams

Authors & Affiliations

T. G. Blackburn ^1,*, E. Gerstmayr ², S. P. D. Mangles ², and M. Marklund¹

¹Department of Physics, University of Gothenburg, SE-41296 Gothenburg, Sweden
²The John Adams Institute for Accelerator Science, Imperial College London, London SW7 2AZ, United Kingdom

^*tom.blackburn@physics.gu.se

Article Text

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Issue

Vol. 23, Iss. 6 — June 2020

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Images

Figure 1
Parallel and perpendicular standard deviations of the angular profile of the radiation emitted by an electron beam with mean initial energy 500 (orange) and 1000 MeV (blue), as predicted by Eqs. (1) and (2) with (solid curves) and without RR (dashed curves) and from simulations with the specified radiation-reaction model (points).
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Figure 2
Parallel and perpendicular standard deviations as a function of initial energy spread $m Δ_{i}$ , for an electron beam with mean initial energy $m ⟨ γ_{i} ⟩ = 500$ (orange) and 1000 MeV (blue) colliding with a laser pulse with $a_{0} = 20$ : simulation results with quantum (filled circles), classical (crosses), and no (squares) radiation reaction (as in Fig. 1) and theoretical predictions Eqs. (1) and (2) with (solid curves) and without (dashed curves) RR, assuming that the beam is monoenergetic at the mean energy.
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Figure 3
The $a_{0}$ inferred from simulation results, using Eq. (5), and (inset) the percentage error in the same, for a beam of electrons with normally distributed initial energies (mean $μ$ and standard deviation $Δ$ ) and initial divergence $δ$ colliding with a plane-wave laser pulse with normalized amplitude $a_{0}$ , wavelength $0.8 μ m$ , and FWHM duration $τ$ : (blue) $μ = 250 MeV$ , $Δ = 5 MeV$ , $δ = 1 mrad$ , and $τ = 150 fs$ ; (orange) $μ = 500 MeV$ , $Δ = 50 MeV$ , $δ = 3 mrad$ , and $τ = 20 fs$ ; (green) $μ = 1000 MeV$ , $Δ = 50 MeV$ , $δ = 2 mrad$ , and $τ = 30 fs$ ; and (red) $μ = 200 MeV$ , $Δ = 10 MeV$ , $δ = 2 mrad$ , and $τ = 30 fs$ .
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Figure 4
(a) Energy radiated per unit solid angle (per electron) by an electron beam in a collision with a laser pulse that has peak $a_{0} = 30$ . White arrows indicate the standard deviations of the distributions. (b) Energy spectra of the electrons before the collision (gray, dashed curve) and after, when the beam offset from the laser axis is $x_{b} = 0$ (blue curve) and $x_{b} = w_{0}$ (orange curve). Arrows indicate the mean energy.
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Figure 5
The inferred $a_{0}$ as a fraction of the true $a_{0}$ , for the collision geometry shown in Fig. 4, for different values of $a_{0}$ : from simulations with quantum (filled circles), modified classical (open circles), classical (crosses), and no RR (squares); and as predicted by Eq. (6) for $x_{b} = 0$ (red) and $x_{b} = w_{0}$ (blue).
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Figure 6
The inferred $a_{0}$ as a fraction of the true $a_{0}$ , for the collision geometry shown in Fig. 4, for different beam radii $r_{b}$ : from simulations with quantum (filled circles), modified classical (open circles), classical (crosses), and no RR (squares); and as predicted by Eq. (6) for $x_{b} = 0$ (red) and $x_{b} = w_{0}$ (blue).
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