Search by keywords or author
• High Power Laser Science and Engineering
• Vol. 8, Issue 4, 04000e38 (2020)
Obulkasim Olugh1、2, Zi-Liang Li3, and Bai-Song Xie1、4、*
Author Affiliations
• 1Key Laboratory of Beam Technology of the Ministry of Education, and College of Nuclear Science and Technology, Beijing Normal University, Beijing100875, China
• 2Xinjiang Police College, Urumqi830011, China
• 3School of Science, China University of Mining and Technology, Beijing100083, China
• 4Beijing Radiation Center, Beijing100875, China
• show less

Abstract

Using the Dirac–Heisenberg–Wigner formalism, effects of the asymmetric pulse shape on the generation of electron-positron pairs in three typical polarized fields, i.e., linear, middle elliptical and circular fields, are investigated. Two kinds of asymmetries for the falling pulse length, short and elongated, are studied. We find that the interference effect disappears with the shorter pulse length and that the peak value of the momentum spectrum is concentrated in the center of the momentum space. In the case of the extending falling pulse length, a multiring structure without interference appears in the momentum spectrum. Research results show that the momentum spectrum is very sensitive to the asymmetry of the pulse as well as to the polarization of the fields. We also find that the number density of electron-positron pairs under different polarizations is sensitive to the asymmetry of the electric field. For the short falling pulse, the number density can be significantly enhanced by over two orders of magnitude. These results could be useful in planning high-power and/or high-intensity laser experiments.

1 Introduction

In intense electromagnetic fields the vacuum state is unstable and spontaneously generates electron-positron ( ${e}^{-}{e}^{+}$ ) pairs. This is known as the Schwinger effect, which is one of the highly nontrivial predictions in quantum electrodynamics (QED)[13]. Because of the tunneling nature of the Schwinger effect, this interesting phenomenon is exponentially suppressed and the pair production rate is proportional to $\exp \left(-\pi {E}_{\mathrm{cr}}/E\right)$ , where the corresponding Schwinger critical field strength ${E}_{\mathrm{cr}}={m}_e^2{c}^3/e\mathrm{\hslash}=1.3\times {10}^{18}\ \mathrm{V}/\mathrm{m}$ . The associated laser intensity, e.g., $I=4.3\times {10}^{29}$ W/cm2, is too high and beyond current technological possibilities. Its detection has therefore remained a challenge for many decades[4]. However, current advances in high-power laser technology[57] and forthcoming experimental facilities (for example, the Extreme Light Infrastructure, the Exawatt Center for Extreme Light Studies, and the Station of Extreme Light at the Shanghai Coherent Light Source) have led to the hope of QED predictions entering the realm of observation. On the other hand, using X-ray free-electron laser facilities can in principle yield a strong field at about $E=0.1{E}_{\mathrm{cr}}=1.3\times {10}^{17}\ \mathrm{V}/\mathrm{m}$ [8] and drive interest in studying pair production under super strong fields.