Strong-field QED processes in laser and plasma environments

Highly relativistic particles can probe the QED critical field if they propagate through strong electromagnetic fields, e.g., in a plasma environment [1]. In this regime nonlinear and nonperturbative QED effects become important and thus a complicated interplay between strong-field QED and plasma physics takes place. To render numerical calculations in this regime feasible the so-called QED-PIC approach has been developed [2], which is based on the semiclassical approximation. Recently, we have investigated the validity of the semiclassical approximation by examining the nonlinear Breit-Wheeler process (electron-positron photoproduction) inside a plane-wave laser field in detail [3]. In the talk the difference between classical and quantum absorption of laser energy, the importance of interference effects and the possibility of recollision processes [4] will be discussed. \newline\noindent [1] Di Piazza et al., Rev. Mod. Phys. \textbf{84}, 1177 (2012)\newline\noindent [2] A. Gonoskov et al., Phys. Rev. E \textbf{92}, 023305 (2015)\newline\noindent [3] SM, C.\ H.\ Keitel and A.\ Di Piazza, Phys.\ Rev.\ D \textbf{93}, 085028 (2016)\newline\noindent [4] SM, K. Z. Hatsagortsyan, C. H. Keitel and A. Di Piazza, Phys. Rev. Lett. \textbf{114}, 143201 (2015)