Generation of Polarized Overdense Pair-photon Fireball via Laser-Driven Nonlinear-linear QED Cascade

Abstract

Relativistic, polarized pair-photon fireballs are central to understand the microscopic energy transfer of high-energy astrophysical outflows, yet generating an overdense fireball in the laboratory, especially via an ultraintense laser, remains a formidable challenge. Here, we propose a novel method of laser-driven nonlinear-linear quantum electrodynamics (NL-QED) plasma, that dramatically lowers the laser intensity threshold for dense pair-photon fireball creation. By coupling polarization-resolved linear Breit-Wheeler and Compton processes with strong-field nonlinear radiation, we find that a self-organized NL-QED cascade is ignited in the laser-driven hole boring at currently accessible 10-petawatt intensities ($\sim 10^{22}\ \mathrm{W/cm^2}$). Consequently, we demonstrate the generation of an overdense (pair density $n_{\rm}\simeq 4.1\times 10^{16}\ \mathrm{cm^{-3}}$, gamma-photon density $n_γ\simeq 9.6\times 10^{21}\ \mathrm{cm^{-3}}$), highly polarized, and quasi-neutral fireball. Our method provides a comprehensive framework for studying laser-driven QED plasma and its application in laboratory astrophysics, probing multi-process QED physics.

Figures (6)

• Figure 1: Formation of the QED-active HB cavity and onset of the NL-QED cascade. (a) Laser field $|E_y|$ overlaid with electron density $n_e$ at $t=15~T_0$. (b) Electron density (upper panel) and carbon-ion density (lower panel) at $t=30~T_0$, together with three representative electron trajectories. (c) Enlarged view of the central trajectory in (b), color-coded by the electron quantum parameter $\chi_e$; instantaneous NCS and the associated LBW and LCS channels are indicated schematically. (d) Longitudinal electric field $\tilde{E}_x$ and charge density $\tilde{n}_q$, averaged over $y=0\pm1~\mu$m, at $t=30~T_0$. (e) Gamma-ray density at $t=30~T_0$. (f) Event probabilities $P$ of LBW and NBW versus background-photon density $\rho$ (bottom axis) and laser intensity $a_0$ (top axis), respectively, for projectile photon energies between 4 and 6 MeV; the background-photon energy in LBW varies from 1 to 500 MeV. (g) Same as (f), but for projectile-photon energies between 460 MeV and 560 MeV. The event probability $P$ is calculated by Eqs. (\ref{['LBWprob']}) and (\ref{['NBWprob']}).
• Figure 2: Spatial, spectral, and polarization structure of the final fireball at propagation time $t=70~T_0$. (a)-(c) Density distributions of electrons, positrons, and gamma photons in the $r$-$\theta$ plane of spherical coordinates. (d) Normalized energy spectra of electrons and positrons corresponding to (a) and (b), respectively; the electron spectrum is fitted by a Maxwell-Jüttner distribution. (e) Normalized gamma-photon spectrum corresponding to (c), fitted by a Planckian distribution. (f)-(h) Polarization distributions of electrons, positrons, and gamma photons in the divergence-angle space $(\theta_y,\theta_z)$, where $\theta_y=\arctan(p_y/p_x)$ and $\theta_z=\arctan(p_z/p_x)$.
• Figure 3: Energy conversion, pair production, and the role of L-QED processes. (a) Time evolution of the laser absorption rate $\Upsilon_{\rm laser}$ for three cases: NL-QED off, NL-QED on, and L-QED off, together with the gamma-photon energy fraction $\Upsilon_\gamma$. (b) Time evolution of the positron yield $\log_{10}(N_{e^+})$ for three cases: NL-QED on, LCS off, and pair radiation off, together with the peak interfacial field $E_{x,p}^{\rm IF}$. (c) and (d) Comparison of angular distributions of gamma-ray number, $\log_{10}[{\rm d}^2N_\gamma/({\rm d}\theta_y{\rm d}\theta_z)]$ at intermediate time $t=30~T_0$, between the cases LCS on and LCS off, respectively. (e) and (f) Comparison of fireball spectra $\log_{10}({\rm d}N/{\rm d}\varepsilon)$ at intermediate time $t=30~T_0$, between the cases LCS on and LCS off, respectively.
• Figure 4: Recirculating acceleration inside the hole-boring cavity. (a) and (b) Snapshots of the longitudinal electric field $E_x$ and charge density $n_{q}$ at $t=30~T_0$. (c) Time evolution of the longitudinal momentum $p_x$ of sampled electrons, color-coded by the longitudinal work $W_x$; (d) corresponding ensemble-averaged longitudinal momentum $\overline{p_x}$ and work $\overline{W_x}$. (e) Same as (c), but for the transverse momentum $p_y$ and transverse work $W_y$; (f) corresponding ensemble-averaged transverse momentum $\overline{p_y}$ and work $\overline{W_y}$.
• Figure 5: Benchmark of cross sections and conservation laws. (a), (c) and (e) Theoretical curves (The.) and simulated results (Sim.) for the yields of LBW electron, LCS electron, and LCS positron versus incident gamma energy. (b), (d), (f) Relative variations of the total energy and momentum varying with simulating time steps, during beam-beam collisions corresponding to (a), (c) and (e), respectively.