  We calculate the momentum spectrum of electron-positron pairs created via the
Schwinger mechanism by a class of four-dimensional electromagnetic fields
called e-dipole fields. To the best of our knowledge, this is the first time
the momentum spectrum has been calculated for 4D, exact solutions to Maxwell's
equations. Moreover, these solutions give fields that are optimally focused,
and are hence particularly relevant for future experiments. To achieve this we
have developed a worldline instanton formalism where we separate the process
into a formation and an acceleration region.
