Subthreshold pair production in short laser pulses

TL;DR

This paper investigates how short, few-cycle laser pulses can significantly enhance electron-positron pair production below the usual energy threshold, due to the pulse's finite bandwidth effects.

Contribution

It introduces a folding model that explains subthreshold pair production enhancement by considering the laser pulse's frequency spectrum and intensity distribution.

Findings

Subthreshold pair production is enhanced in short laser pulses.

Finite bandwidth of pulses causes this enhancement.

The folding model accurately describes the interplay of spectrum and intensity.

Abstract

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 $\sqrt{s} = 2m$ a similar enhancement of the pair production rate as for circular polarization. The strong subthreshold enhancement 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.