Generation of overdense and high-energy electron-positron-pair plasmas by irradiation of a thin foil with two ultraintense lasers

A scheme for enhanced quantum electrodynamics (QED) production of electron-positron-pair plasmas is proposed that uses two ultraintense lasers irradiating a thin solid foil from opposite sides. In the scheme, under a proper matching condition, in addition to the skin-depth emission of $\gamma$-ray photons and Breit-Wheeler creation of pairs on each side of the foil, a large number of high-energy electrons and photons from one side can propagate through it and interact with the laser on the other side, leading to much enhanced $\gamma$-ray emission and pair production. More importantly, the created pairs can be collected later and confined to the center by opposite laser radiation pressures when the foil becomes transparent, resulting in the formation of unprecedentedly overdense and high-energy pair plasmas. Two-dimensional QED particle-in-cell simulations show that electron-positron-pair plasmas with overcritical density ${10}^{22}{\mathrm{cm}}^{-3}$ and a high energy of 100s of MeV are obtained with 10 PW lasers at intensities ${10}^{23}\mathrm{W}/{\mathrm{cm}}^2$, which are of key significance for laboratory astrophysics studies.

Figure 1

The density maps in units of $n_c$ of the ${\mathrm{Al}}^{13+}$ ions [(a) and (e)], emitted $\gamma$-ray photons [(b) and (f)], and created positrons [(c) and (g)] at $t=9T_0$ (upper row) and $18T_0$ (bottom row), respectively, where two ultraintense lasers at the same intensities $I_0=3.4\times {10}^{23}\mathrm{W}/{\mathrm{cm}}^2$ irradiate a $2\mu \mathrm{m}$ Al foil target from opposite sides. Parts (d) and (h) are the corresponding longitudinal distributions of positron numbers (black) and the longitudinal profiles of the normalized electric fields $E_y$ (red).

Figure 2

The longitudinal profiles of a laser electric field $E_y$ (red) and ${\mathrm{Al}}^{13+}$ density $n_i/n_c$ (black) at $y=0$ and $T=9T_0$ for the cases of a $2\mu \text{m}$ Al foil irradiated by one laser pulse (a) and by two laser pulses (c), respectively, where the laser and target parameters are the same as in Fig. 1. Parts (b) and (d) are, respectively, the angular distributions of the emitted $\gamma$-ray photon energies for two cases. Part (e) is the corresponding energy spectra of foil electrons, pair electrons, and positrons at $t=18T_0$ in Fig. 1. Part (f) shows the evolution with time of the corresponding foil electron density longitudinal profile.

Figure 3

(a) and (c) The density maps of created positrons at $t=18T_0$ when two ultraintense lasers irradiate a solid Al foil, where the foil thickness is chosen to be $l_0=0.5$ (a) and $3.5\mu \mathrm{m}$ (b), respectively, breaking the conditions (3) and (4). All other parameters are the same as those in Fig. 1. Parts (b) and (d) are their longitudinal distributions (black) as well as the longitudinal profiles of electric fields $E_y$ (red), respectively.

Figure 4

The total number of the created positrons (red) and the conversion efficiency (black) from laser to pairs scaling with the laser intensities in our enhanced scheme, where conditions (3) and (4) are satisfied.