T. Wang, X. Ribeyre, Z. Gong, O. Jansen, E. d'Humieres, D. Stutman, T. Toncian, and A. Arefiev, "Power scaling for collimated gamma-ray beams generated by structured laser-irradiated targets and its application to two-photon pair production", Phys. Rev. Applied 13, 054024 (2020).
Using three-dimensional kinetic simulations, we examine the emission of collimated γ -ray beams from structured laser-irradiated targets with a prefilled cylindrical channel and its scaling with laser power (in the multi-PW range). The laser power is increased by increasing the laser energy and the size of the focal spot while keeping the peak intensity fixed at 5×1022 W/cm2. The channel radius is increased proportionally to accommodate the change in laser spot size. The efficiency of conversion of the laser energy into a beam of MeV-level γ rays (with a 10o opening angle) increases rapidly with the incident laser power P before it roughly saturates above P ≈ 4 PW. Detailed particle tracking reveals that the power scaling is a result of enhanced electron acceleration at higher laser powers. One application that directly benefits from such a strong scaling is pair production via two-photon collisions. We investigate two schemes for generating pairs through the linear Breit-Wheeler process: colliding two γ-ray beams and colliding one γ-ray beam with black-body radiation. The two scenarios project up to 104 and 105 pairs, respectively, for the γ -ray beams generated at P = 4 PW. A comparison with a regime of laser-irradiated hollow channels corroborates the robustness of the setup with prefilled channels.