High-energy-density positron and ?-photon generation via two counter-propagating ultra-relativistic laser irradiating a solid target

By using two counter-propagating ultra-intense lasers interaction with a solid aluminum (Al) target, an all-optical scheme was demonstrated with the generation of high-bright GeV photons and high energy density electron-positron pairs. The multi-photon Breit-Wheeler (BW) process is simulated by Particle-in-cell (PIC) code EPOCH with a quantum electrodynamics (QED) module implemented. The target front side keeps still due to the involvement of hot electrons in the target in two colliding laser schemes. High-frequency photons are produced by hot electrons colliding with the reflected laser pulse at the front of the target, followed by electron and positron pairs production. On the lateral side of the target, electron bunches are extracted from the target by the p-polarized laser electromagnetic field and accelerated by the laser pondermotive force to collide with the counter-propagating laser. By modulating the target transversal size, the pulse energy is allocated to the target front side and lateral side. It is found that on the lateral side the laser will be more efficient in the generation of gamma photons and positrons, which may helpful for investigating high-energy pair production and gamma-ray emission. The generated positrons are as dense as 40 n(c) and can be accelerated to over 1 GeV. On the target longitudinally front side, the participation of hot electrons in the target plays an important role in the generation of photons and positrons. When the target length is set to the corrected skin depth of the plasma, electrons are fully involved in photon production. The pairs yield reaches 1.68 x 10(11), whose density is 90 n(c). These findings propose a feasible scheme to produce high-energy and high-density pair plasma for extensive scientific research and applications.