Development of a novel gamma detector for the LUXE strong-field QED experiment at DESY

The dynamics of particle motion in intense electromagnetic fields is characterized by a strong non-linearity and radiation emission. Quantum electrodynamics in strong fields is the theory describing the dynamics of charge particles in such environments, whose understanding is crucial for several physical environments: from astrophysics systems to nuclear and future-collider physics. The advent of high-power laser technology renewed the interest in the investigation of such regime, with a considerable theoretical and experimental effort in characterizing this strong field regime with counter-intuitive new phenomena long-predicted by theory (i.e., Sauter-Schwinger pair production). This is the scientific context for the `Laser Und XFEL Experiment' at DESY, where the transition to the strong field regime of quantum electrodynamics will be characterized. This work is divided in two parts. In Part I, non-linear electrodynamics in intense background field is introduced. The main characteristics and theoretical tools for its description are consistently given, and the scientific opportunities from its study are presented. Lastly, the science case of the LUXE experiment is discussed. In Part II, the research activity carried on during the doctoral program is presented. As a first step, an introduction is given to the challenges in characterizing the strong field processes (specifically, the normalized field amplitude) in beam-laser SFQED experiments. The theory discussion on the measurement of the laser intensity is followed by the introduction of the Gamma Beam Profiler sapphire micro-strip detector. Finally, the results from the sapphire research and development campaign to design, develop and characterize such a detector are presented.