Pair Creation with Strong Laser Fields, Compton Scale X Rays, and Heavy Nuclei

Electron-positron pair creation is considered when intense laser pulses collide head-on with $<1\mathrm{MeV}$ x-ray photons in the presence of stationary Coulomb charges $Z(-e)$. The analysis employs Coulomb-corrected Volkov states and is not limited to Born’s approximation in $Z$. The cross section and the yield increase dramatically with increasing $Z$, potentially enabling (i) measurable yields with petawatt lasers and (ii) sensitive tests of strong-field QED.

Figure 1

Production of $e^{-}\text{−}{e}^{+}$ pair, described by plane waves with momenta $p_{-},-p_{+}$. Tree-level diagrams with weak photon fields. Bare-fermion propagator labeled by $i{S}_F$. (a) Breit-Wheeler process with photons $(k_1,{ϵ}_1)$ and $(k_2,{ϵ}_2)$. (b) Bethe-Heitler process with photon $(k,ϵ)$ and nucleus $Z(-e)$. Time axis points upward.

Figure 2

(a) Experimental arrangement for pair production using laser ($k$), x ray ($k_X$), and Coulomb charges [$Z(-e)$]. Laser beam propagates along the $z$ axis with electric field polarized along the $y$ axis (vertical). Figure-eight orbit of leptons in the laser field lies in the plane of the paper. (b) Leptons described by actions $S_{-},S_{+}$. External (thick) lines in (b) depict Coulomb-corrected Volkov states (Furry representation [2]). X-ray field is assumed weak.

Figure 3

(a) Yield (pairs per laser shot) versus nuclear charge $Z$ for 10 PW laser and x-ray photons with normalized energy $\kappa =0.925$, 0.95, 0.98, with other parameters listed in Table 1. (b) Yield versus nuclear charge $Z$ for 1 EW laser and x-ray photons with normalized energy $\kappa =0.6$, 0.75, 0.925. In (a) and (b) strict convergence is maintained on the solid line segments only. (c) Momentum distribution of $e^{-}\text{−}{e}^{+}$ for 10 PW case, $\kappa =0.98$, and $Z=18$. The laser beam propagates along the $z$ axis with electric field polarized along the $y$ axis. Leptons are ejected in opposite directions along the $y$ axis and $\delta p_y\equiv p_{-}^2+p_{+}^2$ measures the difference between their $y$ momenta [Eq. (2) in Supplemental Material [80] ]. Distribution in $p_y\text{−}{p}_z$ plane, given by Eq. (4), is symmetric about $p_y=0$ with vertex on $p_z$ axis given by Eq. (3).