  We study the pair-production process in the presence of two
counterpropagating linearly polarized short laser pulses. By means of a
nonperturbative technique, we take into account the full coordinate dependence
of the external field going beyond the dipole and standing-wave approximations.
In particular, we analyze the momentum distribution of particles created. It is
demonstrated that the spatial variations of the laser pulses may play a crucial
role. The more accurate treatment reveals a number of prominent features: the
pair-production probabilities become considerably smaller, the quantitative
behavior of the momentum spectra changes dramatically, and the pulse shape
effects become much less pronounced. The results of our study are expected to
be very important for future theoretical and experimental investigations.
