Towards Precision Measurements of Strong-Field QED: Amplifying Pair Creation with Polarised Gamma Rays

Abstract

High-intensity lasers can be used to create extremely strong electromagnetic fields and accelerate charged particles to ultra-relativistic energies. In the combination of such fields and high-energy particles, the quantum nonlinear parameter χ approaches unity, the light-matter interactions turn nonlinear and perturbative QED is expected to break down. Then, processes such as Compton scattering and electronpositron pair production become much more likely, ultimately to a point where they forma cascade. We know that Compton-scattered photons (γ-rays) are mostly polarised along the laser’s electric field, and that pair creation is dependent on the γ-ray polarisation; therefore it should be a measurable quantity. In this thesis, we show that the effect of polarisation dependence of pair creation is significant (up to a 12% difference in yield). However, measuring this is experimentally difficult in a typical laser-matter interaction, as the effective χ is sensitive to fluctuations in laser intensity and alignment of the laser and the electron beam, as well as the kinetic energy of the electrons. If we instead consider a more advanced setup, where the electron beam is used at an earlier stage to generate a photon beam via inverse Compton scattering which then collides with a second laser beam, the signal can be enhanced and controlled. These results are relevant for upcoming precision experiments in strong-field QED such as LUXE (Light Und XFEL Experiment).