  The mechanism of laser-driven relativistic pair-jet production qualitatively
changes as laser intensity exceeds $I\gtrsim5\times10^{22}$ W/cm$^{2}$ because
of the appearance of laser-induced strong-field QED processes. Here, we show
that by exceeding this intensity additional physics operates and opens a new
and efficient channel to convert laser photons into dense pair-jets -- the
combination of nonlinear Compton scattering and the Bethe-Heitler process. This
channel generates relativistic electron-positron jets more than three orders of
magnitude denser than has so far been possible. We find that the process is so
efficient that it leads to the prolific production of heavier pairs as well.
The jets produced by this new channel will enable the study of collective
processes in relativistic electron-positron plasmas.
