Deciphering in situ electron dynamics of ultrarelativistic plasma via polarization pattern of emitted $\ensuremath{\gamma}$-photons

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Deciphering in situ electron dynamics of ultrarelativistic plasma via polarization pattern of emitted $γ$ -photons

Zheng Gong, Karen Z. Hatsagortsyan, and Christoph H. Keitel

Phys. Rev. Research 4, L022024 – Published 29 April 2022

Abstract

Understanding and interpretation of the dynamics of ultrarelativistic plasma is a challenge, which calls for the development of methods for in situ probing the plasma dynamical characteristics. We put forward a new method, harnessing polarization properties of $γ$ -photons emitted from a non-prepolarized plasma irradiated by a circularly polarized pulse. We show that the angular pattern of $γ$ -photon linear polarization is explicitly correlated with the dynamics of the radiating electrons, which provides information on the laser-plasma interaction regime. Furthermore, with the $γ$ -photon circular polarization originating from the electron radiative spin flips, the plasma susceptibility to quantum electrodynamical processes is gauged. Our study demonstrates that the polarization signal of emitted $γ$ -photons can be a versatile information source, which would be beneficial for the research fields of laser-driven plasma, accelerator science, and laboratory astrophysics.

Received 27 October 2021
Revised 15 February 2022
Accepted 11 April 2022

DOI:https://doi.org/10.1103/PhysRevResearch.4.L022024

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. Open access publication funded by the Max Planck Society.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Beam polarization Gamma-ray generation in plasmas High intensity laser-plasma interactions Laboratory studies of space & astrophysical plasmas Laser-plasma interactions Polarization in interactions & scattering Ultrashort pulses

Relativistic plasmas

Accelerators & BeamsPlasma Physics

Authors & Affiliations

Zheng Gong ^*, Karen Z. Hatsagortsyan ^†, and Christoph H. Keitel

Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany

^*gong@mpi-hd.mpg.de
^†k.hatsagortsyan@mpi-hd.mpg.de

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Vol. 4, Iss. 2 — April - June 2022

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Plasma Physics

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Figure 1
(a) The schematic for $γ$ -photon emissions from a plasma (with $y < 0$ clipped) interacting with a laser pulse. (b) The LP orientation along the local azimuthal direction. The analytically predicted LP orientation for the electron undergoing acceleration (c) and deceleration (d). The simulated $γ$ -photon LP for the time at (e) $t = 10$ and (f) $40 fs$ , with the LP degree $P_{LP}$ and the normalized number distribution $d^{2} {\tilde{N}}_{p h} / sin θ d θ d ϕ$ . In (b)–(f), the angular distribution is shown in the space of $(θ, ϕ)$ , where $θ = arctan [{(p_{y}^{2} + p_{z}^{2})}^{1 / 2} / p_{x}]$ and $ϕ = arctan 2 (p_{z}, p_{y})$ characterize the momentum direction of emitted $γ$ -photons. (g) The time evolution of the electron energy spectrum $d N_{e} / d ɛ_{e}$ , the polarization orientation $δ ϕ$ , and the kinetic energy $E_{e}$ of electrons with $γ_{e} > a_{0}$ .
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Figure 2
The angular distribution of (a) polarization angle $δ ϕ (θ)$ and (b) LP degree $P_{L P} (θ)$ for three distinct regimes of SRO (red), MRO (black), and LBE (blue). The shadow area is marked for comparison with Fig. 3 and Fig. 4.
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Figure 3
The electron dynamics of the SRO regime. (a) The time evolution of the electron's angle $θ$ with blue-red color denoting $- β \cdot E$ and $γ$ -photon emissions marked by yellow circles. The thin black lines represent different electrons. The blue dashed line refers to $γ_{e}$ . (b) The evolution of the representative electrons in $(Ψ, γ_{e})$ space. (c) The evolution of the electron in $(θ, ϕ)$ space, where the background color manifests the detected $δ ϕ (θ, ϕ)$ . The rainbow color in (b) and (c) refers to the time.
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Figure 4
The electron dynamics of the MRO regime. (a) The same as Fig. 3 but for the MRO regime, where the dashed blue line denotes the normalized field ${\tilde{E}}_{x} = | e | E_{x} / m_{e} c ω_{0}$ . (b) The single-electron trajectory (circles) and evolution tendency of a bunch of electrons (small dots) in $(Ψ, γ_{e})$ space, where the rainbow color refers to time. (c) The dependence of the $γ$ -photon number distribution ${\tilde{N}}_{p h}$ on $- v \cdot E$ and $θ$ , where the dashed line shows ${\tilde{N}}_{p h} (- v \cdot E)$ and the dotted line displays the symmetry of ${\tilde{N}}_{p h} (- v \cdot E < 0)$ at $- v \cdot E > 0$ for comparison.
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Figure 5
The electron dynamics of the LBE regime. (a) The representative electron trajectory in $(x, y)$ plane, where the yellow circles denote the emitted $γ$ -photons with energy $ɛ_{p h} > 10 m_{e} c^{2}$ . (b) The time evolution of the photon emission power $d ɛ_{p h} / d t$ .
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Figure 6
The range of the different regimes presented in the parameter space of $a_{0}$ and $n_{e}$ : (a) for $l_{0} = 10 μ m$ and (b) for $a_{0} = 350$ . The markers denote the regimes of SRO (triangles), MRO (circles), and LBE (crosses) identified by the simulation results of $δ ϕ (θ)$ . The dashed and dotted lines refer to $n_{e}^{†}$ and $n_{e}^{*}$ , respectively.
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Physical Review Research

Deciphering in situ electron dynamics of ultrarelativistic plasma via polarization pattern of emitted γ-photons

Zheng Gong, Karen Z. Hatsagortsyan, and Christoph H. Keitel

Phys. Rev. Research 4, L022024 – Published 29 April 2022

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Deciphering in situ electron dynamics of ultrarelativistic plasma via polarization pattern of emitted $γ$ -photons