Enhancing pair production with optimized chirped laser fields

TL;DR

This work analyzes electron-positron pair production in vacuum under optimized chirped laser fields using the quantum Vlasov equation. It first characterizes the momentum spectra and density produced by a Gaussian chirp, showing interference patterns and a four-order density enhancement relative to chirp-free fields. It then compares five chirp profiles—Gaussian, frequency-modulated, linear, quadratic, and sinusoidal—finding that sinusoidal chirp yields the largest densities and enhancement factors, with a maximum density of $n^{\max}_\mathrm{S}=1.698\times10^{-2}\ \mathrm{m}^{-3}$ and a peak enhancement $n/n_0=1.74\times10^{9}$ at optimal parameters. The results establish clear optimization criteria for chirp parameters and spectral content that markedly amplify vacuum pair production, offering guidance for future experimental validation and control of EP pair creation. Overall, the study demonstrates that spectral broadening and high-frequency components from carefully tailored chirped fields can substantially enhance pair production via the dynamically assisted Schwinger mechanism.

Abstract

The optimal chirped field for enhancing electron-positron (EP) pair production is explored using a quantum kinetic approach. First, the momentum spectrum and number density of EP pairs produced by Gaussian chirped fields are investigated. The results show that the momentum spectrum exhibits distinct interference patterns, while the number density grows monotonically with chirp parameters but oscillates with the carrier angular frequency. Moreover, the number density increases by four orders of magnitude compared to chirp-free fields. The results are further compared with those from four other chirped fields: frequency-modulated, linear, quadratic, and sinusoidal chirp. The analysis reveals that the maximum number density for sinusoidally chirped fields is the highest, followed by Gaussian, frequency-modulated, quadratically, and linearly chirped fields. This ranking also applies to the maximum enhancement factors for these chirped fields. Notably, the number density for sinusoidally chirped fields improves nine orders of magnitude compared to chirp-free fields. These results not only deepen our understanding of pair production in chirped fields but also provide significant optimization strategies for future vacuum pair production experiments.

Figures (8)

• Figure 1: The frequency spectra of the Gaussian chirped electric fields for different values of the carrier angular frequency $\omega_0$. (a) $\omega_{0}=0.3m$ , (b) $\omega_{0}=0.4m$, (c) $\omega_{0}=0.5m$, and (d) $\omega_{0}=0.6m$. The peak positions are also shown in the figures. Other electric field parameters are $E_{0}=0.1E_{\mathrm{cr}}$, $\tau=20/m$, $b=0.1m$, and $\omega_{m}=30/m$.
• Figure 2: The longitudinal momentum spectra ($\mathbf{p}_\perp=0$) of EP pairs produced by Gaussian chirped electric fields for different values of the carrier angular frequency $\omega_0$. (a) $\omega_{0}=0.3m$, (b) $\omega_{0}=0.4m$, (c) $\omega_{0}=0.5m$, and (d) $\omega_{0}=0.6m$. The peaks in the momentum spectra are marked with $1\sim9$. Other electric field parameters are $E_{0}=0.1E_{\mathrm{cr}}$, $\tau=20/m$, $b=0.1m$, and $\omega_{m}=30/m$.
• Figure 3: The number density of EP pairs created by a Gaussian chirped electric field, as a function of the chirp parameter $b$ and the carrier angular frequency $\omega_{0}$, for different values of the chirp parameter $\omega_m$. (a) $\omega_{m}=30/m$, (b) $\omega_{m}=50/m$, (c) $\omega_{m}=100/m$, and (d) $\omega_{m}=1000/m$. Other electric field parameters are $E_{0}=0.1E_{\mathrm{cr}}$ and $\tau=20/m$.
• Figure 4: The number density of EP pairs produced by a chirp-free electric field ($b=0$) as a function of the carrier angular frequency $\omega_{0}$. The peaks marked in the figure correspond to multiphoton absorption thresholds. Other electric field parameters are $E_{0}=0.1E_{\mathrm{cr}}$ and $\tau=20/m$.
• Figure 5: The number density of created EP pairs as a function of chirp parameters and the carrier angular frequency for different chirped electric fields. (a) frequency-modulated chirped electric fields with $\omega_{0}=0.6m$, (b) linearly chirped electric fields, (c) quadratically chirped electric field with $\beta_{1}=0.1$, and (d) sinusoidally chirped electric fields with $b_{6}=1.6$. Other electric field parameters are $E_{0}=0.1E_{\mathrm{cr}}$ and $\tau=20/m$.