  Photoproduction of electron-positron pairs by bremsstrahlung gamma-rays
propagating through a high-intensity optical laser wave is studied. By
calculating total pair production yields as well as energy and angular
distributions of the produced particles for a range of laser intensities, we
analyze the influence that the broad frequency spectrum of bremsstrahlung
exerts on the properties of the process in the transition region between the
perturbative and non-perturbative interaction regimes. In particular, we
demonstrate a continuous shifting of the mainly contributing interval of
bremsstrahlung frequencies during the course of the transition and indicate
characteristic signatures of the laser-dressed particle mass.
