Power Scaling for Collimated γ-Ray Beams Generated by Structured Laser-Irradiated Targets and Its Application to Two-Photon Pair Production

Using three-dimensional kinetic simulations, we examine the emission of collimated gamma-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 x 10(22) W/cm(2). 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 gamma rays (with a 10 degrees opening angle) increases rapidly with the incident laser power P before it roughly saturates above P approximate to 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 gamma-ray beams and colliding one gamma-ray beam with black-body radiation. The two scenarios project up to 10(4) and 10(5) pairs, respectively, for the gamma-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.