  Electron-positron pair production from vacuum in external electric fields
with space and time dependencies is studied numerically using real time
Dirac-Heisenberg-Wigner formalism. The influence of spatial focusing scale of
the electric field on momentum distribution and the total yield of the
particles is examined by considering standing wave mode of the electric field
with different temporal configurations. With the decrease of spatial extent of
the external field, signatures of the temporal field are weaken in the momentum
spectrum. Moreover, in the extremely small spatial extent, novel features
emerge due to the combined effects of both temporal and spatial variations. We
also find that for dynamically assisted particle production, while the total
particle yield drops significantly in small spatial extents, the assistance
mechanism tends to increase in these highly inhomogeneous regimes, where the
slow and fast pulses are affected differently by the overall spatial
inhomogeneity.
