Catalysis of Schwinger vacuum pair production

We propose a new catalysis mechanism for nonperturbative vacuum electron-positron pair production, by superimposing a plane-wave x-ray probe beam with a strongly focused optical laser pulse, such as is planned at the Extreme Light Infrastructure (ELI) facility. We compute the absorption coefficient arising from vacuum polarization effects for photons below threshold in a strong electric field. This setup should facilitate the (first) observation of this nonperturbative QED effect with planned light sources such as ELI yielding an envisioned intensity of order 10(26) W/cm(2).