  Vortex pattern formation in electron-positron pair creation from vacuum by a
time-dependent electric field of linear polarization is analyzed. It is
demonstrated that in such scenario the momentum distributions of created
particles exhibit vortex-antivortex pairs. Their sensitivity to the laser field
parameters such as the field frequency and intensity is also studied.
Specifically, it is shown that with increasing field frequency accross the
one-photon threshold additional vortex-antivortex pairs appear. Their location
in the momentum space is consistent with a general threshold behavior of
probability distributions of created electrons (positrons). Namely, while for
small field frequencies the particles tend to be created along the field
polarization direction, for large enough frequencies they are predominantly
generated in the perpendicular direction. Such change in longitudinal and
transverse momentum sharing of created particles occurs accross the one-photon
threshold.
