Asymmetric pulse effects on pair production in chirped electric fields

We investigate the effects of the asymmetric pulse shapes on electron-positron pair production in a field with three different cases of chirping via the real-time Dirac-Heisenberg-Wigner formalism. Our findings reveal the disappearance of interference effects with shorter falling pulse length, and the peak is concentrated on the left side of the momentum spectrum. As the falling pulse length extends, an incomplete multiring structure appears in the momentum spectrum. The number density of particles are very sensitive to the asymmetry of the pulse. With a long falling pulse, the number density can be significantly enhanced by over four orders of magnitude when certain frequency chirps are utilized. These results highlight the impact of the effective dynamically assisted mechanism and the frequency chirp on pair creation.

Figure 1

Displaying asymmetric time-dependent electric field with ratio parameter $k=0.5$, $k=1$, $k=2$ and $k=3$. The red dashed line, purple dashed line and solid blue line are corresponding to the field with chirp parameter $b=0{\mathit{m}}^2$, $b=0.001{\mathit{m}}^2$ and $b=0.012{\mathit{m}}^2$, respectively. The chosen parameters are $E_0=0.1E_{\mathrm{cr}}$, $\omega =0.6\mathrm{m}$, ${\tau }_1=10/\mathrm{m}$ and ${\tau }_2=k{\tau }_1$.

Figure 2

Momentum spectra of particles in the $(q_x,q_y)$ plane with chirp-free ($b=0$). The falling-pulse duration ${\tau }_2=k{\tau }_1$ is compressed, with $k$ varying between 0 and 1. The chosen parameters for the electric field are $E_0=0.1E_{\mathrm{cr}}$, $\omega =0.6\mathrm{m}$, and ${\tau }_1=10/\mathrm{m}$.

Figure 3

Same as Fig. 2 except that the falling pulse length ${\tau }_2=k{\tau }_1$ becomes longer with $k\ge 1$.

Figure 4

Same as Fig. 2 except for the small frequency chirp parameter with $b=0.002$.

Figure 5

Same as Fig. 3 except for the small frequency chirp parameter with $b=0.002$.

Figure 6

Same as Fig. 2 except for the large frequency chirp parameter with $b=0.01$.

Figure 7

Same as Fig. 3 except for the large frequency chirp parameter with $b=0.01$.

Figure 8

Number density of particles in asymmetric electric fields with varying pulse length ratio values $k$, measured in units of ${\lambda }_c^{-3}$. The chirp parameters $b$ considered in this research are $0,\dot{0}.002$, 0.005, 0.007, 0.01, and 0.12. The electric field parameters chosen are $E_0=0.1E_{\mathrm{cr}}$, $\omega =0.6\mathrm{m}$, and ${\tau }_1=10/\mathrm{m}$.

Figure 9

Same as Fig. 8, except that the pulse energy is kept constant.