also been discussed in the context of searching for minicharged particles [@Villalba-Chavez:2013txu].

In this paper we study the phenomenon of stimulated photon emission from the vacuum in the presence of a strong space-time dependent electromagnetic field (cf. also [@Galtsov:1971xm]). Focusing on a comparably simple electromagnetic field profile, which should nevertheless capture the essential features of the electromagnetic fields generated in the focal spots of real high-intensity laser beams, we provide estimates for the numbers of emitted photons attainable with present and near future high-intensity laser facilities.

The experimental set-up we have in mind is as follows: A high-intensity laser pulse is split equally into two pulses, which are separated and directed in a counter-propagation geometry. Both pulses are focused such that they evolve along the well-defined envelope of a Gaussian beam and their foci overlap. This results in a macroscopic strong-field region about the beam waist (cf. also Fig. \[fig:cartoon\], below). The superposition of the two counter-propagating electromagnetic waves results in a standing electromagnetic wave which – in contrast to a single plane wave – is characterized by at least one nonzero electromagnetic field invariant. The idea is to look for induced photons emitted from the strong-field region and to 