Power Scaling for Collimated <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>γ</mml:mi></mml:math>-Ray Beams Generated by Structured Laser-Irradiated Targets and Its Application to Two-Photon Pair Production

Abstract

Using three-dimensional kinetic simulations, we examine the emission of collimated $\ensuremath{\gamma}$-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 $5\ifmmode\times\else\texttimes\fi{}{10}^{22}\phantom{\rule{0.2em}{0ex}}\mathrm{W}/{\mathrm{cm}}^{2}$. 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 $\ensuremath{\gamma}$ rays (with a ${10}^{\ensuremath{\circ}}$ opening angle) increases rapidly with the incident laser power $P$ before it roughly saturates above $P\ensuremath{\approx}4\phantom{\rule{0.2em}{0ex}}\mathrm{PW}$. 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 $\ensuremath{\gamma}$-ray beams and colliding one $\ensuremath{\gamma}$-ray beam with black-body radiation. The two scenarios project up to ${10}^{4}$ and ${10}^{5}$ pairs, respectively, for the $\ensuremath{\gamma}$-ray beams generated at $P=4\phantom{\rule{0.2em}{0ex}}\mathrm{PW}$. A comparison with a regime of laser-irradiated hollow channels corroborates the robustness of the setup with prefilled channels.

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