Pulse envelope effects in nonlinear Breit-Wheeler pair-creation

TL;DR

This paper investigates how the shape and edges of laser pulse envelopes affect electron-positron pair creation, revealing interference effects, spectrum broadening, and azimuthal asymmetries in various pulse configurations.

Contribution

It introduces a toy model to identify pulse envelope effects beyond local approaches and links pulse shape to pair creation characteristics.

Findings

Pulse envelope influences pair spectrum and interference patterns.

Broadening of channel openings occurs below local harmonic thresholds.

Azimuthal asymmetry signals pulse envelope interference in transverse momentum distribution.

Abstract

The effect of the pulse envelope on electron-positron pair creation in a circularly-polarised laser pulse is investigated. Interference on the length scale of the pulse envelope, and smoothness of the pulse edges are found to influence the pair spectrum. A toy model of a flat-top pulse is used to identify pulse envelope effects inaccessible to local approaches. Broadening of channel openings and a widening of the energy and transverse momentum distribution of the pair are found to receive contributions that are below the local harmonic threshold. By comparing pair yields in a flat-top, sine-squared and Gaussian pulse, a link between pulse shape and photon-polarised Breit-Wheeler is found. In the transverse momentum distribution, a signal of pulse envelope interference is found in an azimuthal asymmetry, which appears in intense fields and persists in long pulses.