Strong-field quantum electrodynamics in the field of ultra-intense lasers

Abstract

Quantum electrodynamics (QED) is among the most precise theories in physics, with excellent agreement between theory and experiment in the perturbative regime. However, QED in strong background fields remains less explored experimentally due to the challenges in generating such environments. Theoretical studies have proposed various processes and calculation frameworks in this regime, but experimental validation is essential to improve theoretical understanding.

To this end, experiments using ultra-intense laser fields or strong nuclear fields of crystals have been proposed, aiming to probe strong-field QED via the detection of emitted particles. These studies demand advanced detectors capable of withstanding extreme high-energy and high-flux conditions.

This thesis presents the development of two such detection techniques. Firstly, a gamma-ray spectrometer, designed to measure the energy spectra of high flux and energy photon beams is discussed, detailing its operation principles and simulation studies of its expected performance. A first experimental characterisation of the spectrometer is also presented, which involved the measurement of a ~1 GeV bremsstrahlung source.

Secondly, an approach to inferring interaction properties from the spatial profile of a Compton-scattered photon beam is presented. The theory of this method is developed, with numerical studies for different interaction parameters considered, as well as a range of validity for applying the technique. This method is applied to a proposed gamma beam profiler for the LUXE experiment, with simulations demonstrating its effectiveness.

Finally, an experimental setup targeting rare two-photon QED processes, linear Breit-Wheeler production and elastic photon-photon scattering, is examined. The use of current and next-generation PW-class laser facilities is shown to significantly enhance signal yields. Simulation results support order-of-magnitude estimates, suggesting that direct observation and stringent bounds on these processes are feasible.

Date of Award	Jul 2025
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Engineering and Physical Sciences Research Council
Supervisor	Marco Borghesi (Supervisor) & Gianluca Sarri (Supervisor)