Pair plasma formation in the interaction of a thin plasma with ultra-intense counter-propagating lasers

Next-generation lasers (e.g. ELI) expect to reach peak intensities of $\sim 10^{23}$ Wcm$^{-2}$. At such intensities, the electromagnetic field strength is sufficient for non-linear Quantum Electrodynamics effects to become important. The processes of non-linear Compton scattering and Breit-Wheeler Pair production become likely at intensities $\geq 10^{23}$ Wcm$^{-2}$, and have been predicted to lead to prolific pair and $\gamma$-ray production via electromagnetic cascades. We present results for the case of two counter-propagating circularly- polarized lasers of intensity $I\in [10^{23},10^{25}]$ Wcm$^{24}$ interacting with a plasma of initial density $n_0\in [10^{25},10^{35}]$ via the Monte-Carlo- particle-in-cell code EPOCH. We show the maximum pair plasma density in $I$ vs $n_0$ space. We further discuss the variation within this space on the plasma characteristics, including laser absorption and field-particle energy distribution.