Electrons accelerated from a thin foil irradiated by an ultra-intense laser pulse emit energetic photons in the gamma region. The pulse rips electrons out of the initially solid target into the free space in front of it. While the laser pulse still burns through the target, the fast electrons interact with its strong electromagnetic field, producing energetic photons through the process of quantum radiation reaction - a peculiar kind of self-force stemming from higher-order corrections to the Lorentz force only observable in the presence of extremely strong electromagnetic fields, such as those of produced by the ELI lasers.