  We adopt the general formalism for analyzing evolution of gaussian states of
quantized fields in time-dependent backgrounds in the Schrodinger picture
(presented in detail in arXiv:0708.1233 and 0708.1237) to study the example of
a spatially uniform electric field background (in a time-dependent gauge) which
is kept turned on for a finite duration of time. In particular, we study the
\emph{time-dependent} particle content, defined in terms of the concept of
instantaneous eigenstates, and describe how it captures the time evolution of
the quantized field modes. The actual particle creation process occurs over a
relatively short interval in time, and the particle content saturates rather
quickly. We also compare the \emph{power spectrum} of the field modes, computed
in the asymptotic limit, with the corresponding situation in a cosmological de
Sitter background. Particle creation under the influence of a spiked electric
field localized in time, as a particular limiting case of the above general
model, is also considered.
