  Using the Dirac-Heisenberg-Wigner (DHW) formalism, e?ects of asymmetric pulse
shape on the generation of electron-positron pairs in three typical polarized
fields, i.e., the linear, middle elliptical and circular ones, are
investigated. Two kinds of asymmetries for the falling pulse length, one is
compressed and the other is elongated, are studied. It is found that the
interference e?ect disappears with the compression of the pulse length, and
finally the peak value of the momentum spectrum is concentrated in the center
of the momentum space. For the opposite situation by extending the falling
pulse length, a multi-ring structure without interference appears in the
momentum spectrum. Research results exhibit that the momentum spectrum is very
sensitive to the asymmetry of the pulse as well as to the polarization of the
fields. It is also found that the number density of electron-positron pairs
under di?erent polarizations is sensitive to the asymmetry of electric field.
For the compressed falling pulse, the number density can be enhanced
significantly over 2 orders of magnitude. These results could be useful in
planning high power or/and high-intensity laser experiments.
