  We study particle creation in a single pulse of an electric field in scalar
quantum electrodynamics. We first identify parameter regions of the theory
where the dynamical pair creation and Schwinger mechanism respectively dominate
each other. Then, analytical expressions for the total characteristics of
particle creation are determined for the case where the Schwinger mechanism
dominates. We also compare our results with those produced in a constant
electric field with a finite-time interval. These results coincide at a strong
field regime, however they differ in general field strength. We identify the
reason of this difference with a nonperturbative effect of high-frequency
photons in external electric fields.
