近日，俄罗斯圣彼得堡国立大学的 I. A. Aleksandrov与A. A. Andreev合作并取得一项新进展。经过不懈努力，他们实现用于测量超高激光强度的激光等离子体中正电子的产生。相关研究成果已于2024年7月11日在国际知名学术期刊《物理评论A》上发表。

本文探讨了通过测量正电子产率来提取超高激光强度的可能性。研究团队基于两种过程的量子电动力学（QED）速率的数值模拟，提供了在不同设置下正电子总数作为激光强度函数的数据：一种是单个聚焦激光脉冲，另一种是两个反向传播脉冲的组合。作为种子粒子，研究人员考虑了自由电子气体和中性Xe原子气体。

本研究特别关注了超高激光强度下可能发生的对产生级联过程。结果表明，在正电子产生的阈值附近，QED级联的贡献并不显著；即存在一个广泛的强度范围，其中激光场能产生大量正电子，但尚未触发级联过程。在这个范围内，强度诊断尤为准确。通过调整实验装置的几何形状，可以改变相应的激光强度阈值，从而最大限度地提高诊断方案的准确性。

据悉，量子电动力学(QED)预测了在强外场存在下，通过高能光子的衰变产生电子-正电子对的现象。这种光子可以产生由于非线性康普顿散射涉及电子传播在一个强烈的外部背景。

附：英文原文

Title: Positron production in a laser plasma for measuring superhigh laser intensities

Author: I. A. Aleksandrov, A. A. Andreev

Issue&Volume: 2024/07/11

Abstract: Quantum electrodynamics (QED) predicts the phenomenon of electron-positron pair production via the decay of a high-energy photon in the presence of strong external fields. Such photons can be generated due to nonlinear Compton scattering involving electrons propagating in an intense external background. Here we investigate the possibility of extracting superhigh laser intensities by measuring the positron yield. Our numerical simulations based on the QED rates of the two aforementioned processes provide the total number of positrons as a function of the laser intensity for two different setups: a single focused laser pulse and a combination of two counterpropagating pulses. As seed particles, we consider a free-electron gas and a gas of neutral Xe atoms. In this study, special focus is placed on taking into account the cascade process of pair production, which can occur in the case of superhigh laser intensities. It is demonstrated that the contribution of the QED cascade is not important in the vicinity of the positron generation threshold; i.e., an extended intensity domain where the laser field produces a substantial number of positrons but does not yet launch the cascade exists. Within this range, the intensity diagnostics is particularly accurate. By adjusting the geometry of the experimental setup, one can change the corresponding threshold value of the laser intensity in order to maximize the accuracy of the diagnostic scheme.

DOI: 10.1103/PhysRevA.110.013111

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.013111