Stimulated vacuum emission and photon absorption in strong electromagnetic fields

TL;DR

This paper explores how strong electromagnetic fields can stimulate vacuum photon emission and absorption during electron-positron pair production, providing quantitative predictions for experimental detection of nonlinear QED effects.

Contribution

It introduces a detailed analysis of stimulated photon emission and absorption in strong fields using the Furry picture and WKB approach, proposing an experimental setup to observe these effects.

Findings

Stimulated emission adds to vacuum photon production.

Photon absorption reduces the number of detectable photons.

Intensity changes of about 1% are observable at fields above 10^{27} W/cm^2.

Abstract

According to quantum electrodynamics (QED), a strong external field can make the vacuum state decay producing electron-positron pairs. Here we investigate emission of soft photons which accompanies a nonperturbative process of pair production. Our analysis is carried out within the Furry picture to first order in the fine-structure constant. It is shown that the presence of photons in the initial state gives rise to an additional (stimulated) channel of photon emission besides the pure vacuum one. On the other hand, the number of final (signal) photons includes also a negative contribution due to photon absorption within the pair production process. These contributions are evaluated and compared. To obtain quantitative predictions in the domain of realistic field parameters, we employ the WKB approach. We propose to use an optical probe photon beam, whose intensity changes as it traverses a spatial region where a strong electric component of a background laser field is present. It is demonstrated that relative intensity changes on the level of $1 \%$ can be experimentally observed once the intensity of the strong background field exceeds $10^{27}~\text{W/cm}^2$ within a large laser wavelength interval. This finding is expected to significantly support possible experimental investigations of nonlinear QED phenomena in the nonperturbative regime.