Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
Key Laboratory for Laser Plasmas, Ministry of Education, and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China.
Phys Rev Lett. 2019 Oct 25;123(17):174801. doi: 10.1103/PhysRevLett.123.174801.
The generation of ultrarelativistic polarized positrons during the interaction of an ultrarelativistic electron beam with a counterpropagating two-color petawatt laser pulse is investigated theoretically. Our Monte Carlo simulation, based on a semiclassical model, incorporates photon emissions and pair productions, using spin-resolved quantum probabilities in the local constant field approximation, and describes the polarization of electrons and positrons for the pair production and photon emission processes, as well as the classical spin precession in between. The main reason for the polarization is shown to be the spin asymmetry of the pair production process in strong external fields, combined with the asymmetry of the two-color laser field. Employing a feasible scenario, we show that highly polarized positron beams, with a polarization degree of ζ≈60%, can be produced in a femtosecond timescale, with a small angular divergence, ∼74 mrad, and high density, ∼10^{14} cm^{-3}. The laser-driven polarized positron source raises hope for providing an alternative for high-energy physics studies.
超相对论极化正电子在相对论性电子束与反向传播双色皮秒激光脉冲相互作用中的产生进行了理论研究。我们的蒙特卡罗模拟基于半经典模型，结合了使用局部恒场近似中的自旋分辨量子概率的光子发射和对产生，描述了对产生和光子发射过程中电子和正电子的极化，以及两者之间的经典自旋进动。结果表明，强外场中对产生过程的自旋不对称性，结合双色激光场的不对称性，是极化的主要原因。利用一种可行的方案，我们表明，在飞秒时间尺度内，可以产生具有约 60%极化度 ζ 的高度极化正电子束，具有小角发散度，约 74 mrad，以及高密度，约 10^{14} cm^{-3}。激光驱动的极化正电子源为高能物理研究提供了一种替代方案。
