Nonlinear Bound-Free Pair Creation in the Strong Electromagnetic Fields of a Heavy Nucleus and an Intense X-Ray Laser

We study $e^{-}{e}^{+}$ pair creation in the collision of a heavy nucleus with an intense x-ray laser, where the produced $e^{-}$ is simultaneously captured into the $K$ shell of the projectile nucleus. The parameters of the colliding system are chosen such that the absorption of at least two photons from the laser wave is required in order to surmount the energy threshold of the reaction. Considering this fundamental nonlinear strong-field process for the first time, we estimate the total production rate as well as the angular and energetic distributions of the emitted positrons. According to our results, the process of nonlinear bound-free pair creation could become observable by the aid of the upcoming x-ray laser facilities.

Figure 1

Nuclear frame rates for nonlinear pair creation, differential in the polar emission angle of the $e^{+}$. The parameters of the colliding system are $Z=50$, $\gamma =50$, $\hslash \omega =9\mathrm{k}\mathrm{e}\mathrm{V}$, and $F=1.75\times {10}^{11}\mathrm{V}/\mathrm{c}\mathrm{m}$.

Figure 2

Lab frame rates for pair creation, differential in the total energy of the emitted $e^{+}$. The collision parameters are the same as in Fig. 1. Also shown is the rate for bound-free pair creation by a single photon of 18 keV.

Figure 3

Same as Fig. 1, but given in the lab frame.