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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.