7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

QED-induced opacity and dense polarized positrons and electrons generationin laser-solid interaction
Wei-Min Wang1, Huai-Hang Song2, and Yu-Tong Li2
1
Department of Physics, Renmin University of China, Beijing 100872, China
2
Institute of Physics, Chinese Academy of Sciences, Beijing 100190, Chinae-mail (Wei-Min Wang): weiminwang1@ruc.edu.cn
Many works have reported that dense gamma-ray
photons and electron-positron pairs can be effectively
generated from laser-solid interactions in the strong-field
quantum electrodynamics (QED) regime with 10-PW
and 100-PW laser pulses. In particular, such works with
via a conventional laser-solid experimental setup that a
linearly polarized laser pulse irradiates a solid target
arouse significant interests, because this setup isgenerally adopted in current laser-solid experiments andexpected to commonly use in future 100-PW laser-solid
experiments aiming at various applications. Usually, thepreplasma ahead of the target is ignored since therelativistic transparency and laser hole boring make agiven relativistically- underdense preplasma moretransparent with the enhanced laser intensity. Our
QED-PIC shows that such preplasma becomes opaque
when the QED effects is considered, whereavalanchelike QED cascades occur and most laser energy
can be converted to photons and pairs [1].
Whether the created positrons and electrons arepolarized has not yet been reported, limiting theirpotential applications and hindering the insight
investigation of 100-PW-laser solid-plasma interactions.
By a recently developed QED particle-in-cell (PIC) code[2] including electron/positron spin and photon
polarization effects [3], we further investigate theconventional laser-solid setup. We find [4] that once thepair yield becomes appreciable with the laser intensity
reaching 1024 W/cm2, the pairs are obviously polarized
as a function of the deflection angle. Around 30 nC
positrons can acquire >30% polarization degree. The
polarization can reach 60% at some energy spectra. The
angle-dependent polarization is attributed to theasymmetrical laser fields formed near the plasma skinlayer, where radiative spin-flip and radiation reaction
play significant roles. The polarization mechanism isrobust because a skin layer can be certainly formed in theconventional laser-solid setup. Therefore, generation ofpolarized positrons/electrons should be ubiquitous in
future 100-PW-class laser-solid experiments even aiming
at other applications, which suggests thatelectron/positron spin and photon polarization effects
should be considered. Without the two effects, oursimulation preliminarily shows that the positron yield
will be overestimated by about 7%.
References[1]Wei-Min Wang, Paul Gibbon, Zheng-Ming Sheng,Yu-Tong Li, and Jie Zhang, Laser opacity in underdense
preplasma of solid targets due to quantum
electrodynamics effects, Phys. Rev. E 96, 013201 (2017).
[2]Huai-Hang Song, Wei-Min Wang, Yan-Fei Li,Bing-Jun Li, Yu-Tong Li, Zheng-Ming Sheng, Li-Ming
Chen and Jie Zhang, Spin and polarization effects on
the nonlinear Breit-Wheeler pair production inlaser-plasma interaction, New J. Phys. 23, 075005(2021).
[3]Yan-Fei Li, Yue-Yue Chen, Wei-Min Wang, andHua-Si Hu, Production of Highly Polarized PositronBeams via Helicity Transfer from Polarized Electrons ina Strong Laser Field, Phys. Rev. Lett. 125, 044802(2020).
[4]Huai-Hang Song, Wei-Min Wang, and Yu-Tong Li,
Dense Polarized Positrons from Laser-Irradiated Foil
Targets in the QED Regime, Phys. Rev. Lett. 129,035001 (2022).