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Upcoming ultrahigh power lasers at 10 PW level will make it possible to experimentally explore electron-positron (e−e+) pair cascades and subsequent relativistic e−e+ jets formation, which are supposed to occur in extreme astrophysical environments, such as black holes, pulsars, quasars and gamma-ray bursts. In the latter case it is a long-standing question as to how the relativistic jets are formed and what their temperatures and compositions are. Here we report simulation results of pair cascades in two counter-propagating QED-strong laser fields. A scaling of QED cascade growth with laser intensity is found, showing clear cascade saturation above threshold intensity of ~1024 W/cm2. QED cascade saturation leads to pair plasma cooling and longitudinal compression along the laser axis, resulting in the subsequent formation of relativistic dense e−e+ jets along transverse directions. Such laser-driven QED cascade saturation may open up the opportunity to study energetic astrophysical phenomena in laboratory.

Enhanced electron-positron (e−e+) pair production using two obliquely incident lasers interacting with a solid target is investigated through multi-dimensional particle-in-cell (PIC) simulations. Two obliquely incident lasers can strengthen the laser-hole boring effect, which enhances the reflected focusing laser field and the consequent quantum electrodynamics effects. PIC simulations show that by using two 10 PW-scale lasers, a high-yield (3 × 1010) overdense (~1022 cm−3) positron beam can be generated and laser to pair energy conversion efficiency can be increased up to one percent. Such positron yield is fifty times higher than that produced from a single laser with the same peak power. The robustness of such a scheme is confirmed by numerically studying parametric influences of the oblique incident angle, temporal asynchrony and phase difference between the two lasers. It is found that the temporal asynchrony and the phase difference have minor effects on the pair production. The proposed scheme may provide great potential for high dense pair plasma generation in experiments with coming approachable high power laser facilities.

Two-dimensional particle-in-cell simulations have been performed to study electron-positron pair production and cascade development in single ultra-relativistic laser interaction with solid targets. The spatiotemporal distributions of particles produced via QED processes are illustrated and their dependence on laser polarizations is investigated. The evolution of particle generation displays clear QED cascade characters. Studies show that although a circularly polarized laser delays the QED process due to the effective ion acceleration, it can reduce the target heating and confine high-energy charged particles, which leads to deeper QED cascade order and denser pair plasma production than linearly polarized lasers. These findings may benefit the understanding of the coming experimental studies of ultra-relativistic laser target interaction in the QED dominated regime.

A new mechanism of harmonics generation (HG) induced by quantum electrodynamics (QED) effects in extreme intense laser foil interaction is found and investigated by particle-in-cell (PIC) simulations. When two laser pulses with identical intensities of 1.6 × 1024 W cm-2 are counterincident on a thin foil target, harmonics emission is observed in their reflected electromagnetic waves. Such harmonics radiation is excited due to transversely oscillating electric currents coming from the vibration of QED effect generated e-e+ pairs. The effects of laser intensity and polarization were studied. By distinguishing the cascade depth of generated photons and pairs, the influence of QED cascades on HG was analyzed. Although the current HG is not an efficient way for radiation source applications, it may provide a unique way to detect the QED processes in the near future ultra-relativistic laser solid interactions.

Electron-positron ( e − e + ) pair plasma generation in the relativistic transparency regime in a thin foil with a fixed thickness irradiated by two counter-propagating laser pulses is investigated through multi-dimensional particle-in-cell simulations. It is shown that target transparency can significantly enhance the pair generation due to the formation of a stable standing wave. An optimum foil density of 200–280 n c (with nc being the critical plasma density of the incident laser at the wavelength of 1 μm) is found for enhanced e − e + pair generation for laser intensity around 10 PW. With such foil density, laser energy transformed to pair plasma formation is approximately four times higher than that with a foil density of 710 nc, while the laser energy transformed to γ-photons remains almost the same. Dense e − e + plasma with a density as high as 10 22 cm − 3 ( ≃ 10 n c ) can be produced accordingly. Comparison of pair plasma generation between cases with fundamental and double frequency driv...

Pair production from the Breit-Wheeler process in ultra-intense laser pulse interactions with solid targets are studied by particle-in-cell simulations using the EPOCH code including the quantum electrodynamics module. We find that the pair yield depends on both the target transverse size and the laser pulse duration. For a short laser pulse, the highest pair yield is achieved with a target as wide as the laser spot size. For a long laser pulse, however, the optimal target size for the pair production increases with the pulse duration due to a self-generated cone by the hole-boring process. The effect of laser polarization upon the pair production is also studied. It is found that a circularly polarized laser pulse is more efficient in the ion acceleration rather than in the pair production. With the same laser energy, we find that a linearly polarized laser pulse can generate two times more positrons than the circularly polarized laser pulse does. These findings may benefit the future researches on the l...