Effect of laser polarization on QED cascading

TL;DR

This paper numerically investigates how laser polarization affects QED cascade development, revealing that circular polarization produces more particles overall, while linear polarization leads to more complex, region-dependent dynamics.

Contribution

The study extends the qualitative model of laser-assisted QED cascades by incorporating the effects of laser polarization, highlighting differences in cascade behavior between linear and circular polarizations.

Findings

Circular polarization yields more particles for the same laser energy.

Linear polarization creates electric and magnetic regions affecting cascade dynamics.

Cascade growth rate is stable in circular polarization but varies periodically in linear polarization.

Abstract

Development of QED cascades in a standing electromagnetic wave for circular and linear polarizations is simulated numerically with a 3D PIC-MC code. It is demonstrated that for the same laser energy the number of particles produced in a circularly polarized field is greater than in a linearly polarized field, though the acquiring mean energy per particle is larger in the latter case. The qualitative model of laser-assisted QED cascades is extended by including the effect of polarization of the field. It turns out that cascade dynamics is notably more complicated in the case of linearly polarized field, where separation into the qualitatively different "electric" and "magnetic" regions (where the electric field is stronger than the magnetic field and vice versa) becomes essential. In the "electric" regions acceleration is suppressed and moreover the high-energy electrons are even getting cooled by photon emission. The volumes of the "electric" and "magnetic" regions evolve periodically in time, and so does the cascade growth rate. In contrast to the linear polarization the charged particles can be accelerated by circularly polarized wave even in "magnetic" region. The "electric" and "magnetic" regions do not evolve in time and cascade growth rate almost does not depend on time for circular polarization.