Finite size effects in stimulated laser pair production

TL;DR

This paper investigates how finite laser pulse sizes affect stimulated pair production in strong-field QED, revealing discrete resonance conditions in infinite waves and broadening effects in finite pulses, with implications for multi-photon pair creation.

Contribution

It demonstrates the transition from discrete to continuous momentum transfer in pair production as laser pulses become finite, linking resonance patterns to diffraction phenomena.

Findings

Resonance conditions are discrete in infinite plane waves.

Finite pulses cause broadening and sub-threshold pair production.

Resonance patterns resemble diffraction interference effects.

Abstract

We consider stimulated pair production employing strong-field QED in a high-intensity laser background. In an infinite plane wave, we show that light-cone quasi-momentum can only be transferred to the created pair as a multiple of the laser frequency, i.e.\ by a higher harmonic. This translates into discrete resonance conditions providing the support of the pair creation probability which becomes a delta-comb. These findings corroborate the usual interpretation of multi-photon production of pairs with an effective mass. In a pulse, the momentum transfer is continuous, leading to broadening of the resonances and sub-threshold behaviour. The peaks remain visible as long as the number of cycles per pulse exceeds unity. The resonance patterns in pulses are analogous to those of a diffraction process based on interference of the produced pairs.