  The resonant external field-assisted Breit-Wheeler process (Oleinik
resonances) for strong electromagnetic fields with intensities less than the
critical Schwinger field has been theoretically studied. The resonant
kinematics has been studied in detail. The case of high-energy initial gamma
quanta and emerging ultrarelativistic electron-positron pairs is studied. The
resonant differential cross section is obtained. The generation of narrow beams
of ultrarelativistic positrons (for Channel A) and electrons (for Channel B) is
predicted with a probability significantly exceeding corresponding to the
non-resonant process.
