Carrier envelope phase and laser pulse shape effects on Schwinger vacuum pair production in super-Gaussian asymmetric electric fields

TL;DR

The paper analyzes how carrier-envelope phase $\varphi$ and laser-pulse shape affect Schwinger vacuum pair production in an asymmetric time-dependent field by solving the quantum Vlasov equation for a subcritical field $E_0 \ll E_{\text{cr}}$. Using a field profile $E(t)$ with a super-Gaussian envelope of order $\nu$ and falling/rising asymmetry $\beta$, they compute momentum spectra and the asymptotic density $n(\infty)$, revealing extreme sensitivity to these parameters. A semiclassical turning-point (WKB) analysis explains the observed interference patterns, including ring-like multiphoton structures corresponding to photon numbers (e.g., $n=4$ and $n=5$), and shows how turning-point towers evolve with $\beta$. The results indicate that increasing $\nu$ and optimizing $\varphi$ and $\beta$ can enhance pair production by up to 2–3 orders of magnitude in certain parameter regimes, offering practical guidance for experiments at future high-intensity facilities.

Abstract

We investigate the combined effects of carrier envelope phase and laser pulse shape on electron-positron pair production in the presence of an external asymmetric super-Gaussian electric field by solving the quantum Vlasov equation. By varying the field asymmetry, the pulse shape from Gaussian to super-Gaussian, and the carrier envelope phase, we show the momentum distribution and the number density of created pairs to exhibit extreme sensitivity to these field characteristics. The effects are also qualitatively explained by analyzing the turning-point structures within the WKB formalism. We observed that multiphoton pair production dominates in the case of long falling-pulse asymmetry. For a short falling pulse with a flat-top super-Gaussian laser profile, pair production is further facilitated. For certain field parameters, we demonstrate that the number density can be enhanced by two to three orders of magnitude.

Figures (15)

• Figure 1: Schematic of the electric field \ref{['eq:field_profile']} with variation in $\beta$ and $\varphi$. Rest of the field parameters are $E_0 = 0.2\, E_\text{cr}, \omega = 0.5\, m, \tau_1 = 8.0/m$ and $\nu = 1.0$.
• Figure 2: Same as Fig. \ref{['fig:field_profiles_gaussian']} except for $\nu = 5.0$.
• Figure 3: Momentum spectra in the plane ($k_z, k_x$) at $k_y = 0$ for Gaussian asymmetric fields with varying pulse asymmetry parameter $\beta$. The plot illustrates the effect of compressed falling pulse duration i.e., $\beta < 1$. The other field parameters are $E_0 = 0.2\, E_\text{cr}$, $\omega = 0.5\, m$, $\tau_1 = 8.0/m$, $\varphi = 0$, and $\nu = 1.0$.
• Figure 4: Same as Fig. \ref{['fig:MD_beta<1_phi0_nu1']} except for elongated falling pulse duration i.e., $\beta>1$.
• Figure 5: Ring-like structure in multiphoton pair production: Momentum spectrum showing outer circle $C_1$ (radius $0.711$ m) and inner circle $C_2$ (radius $0.200$ m). The electric field parameters are $E_0 = 0.2\, E_\text{cr}, \omega = 0.5\, m, \tau_1 = 8.0/m$, and $\beta = 10.0$, $\varphi = 0$ and $\nu = 1.0$.