Pair production in short laser pulses near threshold

The e+e− pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit–Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold s=2m a similar enhancement of the pair production rate as for circular polarization. The strong enhancement below the weak-field threshold is traced back to the finite bandwidth of the laser pulse. A folding model is developed which accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.