The driving theme of this thesis is the experimental production and characterisation of high-energy gamma radiation using a laser wakefield accelerator (LWFA), and its application in the context of studies of fundamental QED phenomena.

An electron beam from shock injection of an energy up to 1.3 GeV was collided with a laser pulse at an intensity of a0 ~ 0.2 - 1 producing 10's of MeV photons from linear inverse Compton scattering (ICS). The emitted radiation was used to diagnose the properties of the electron beam and of the laser pulse at the interaction. It was demonstrated that this can also be used to systematically facilitate the spatio-temporal overlap of the electron beam and the laser pulse in future radiation reaction studies.

A relativistic electron beam of energy > 500 MeV was collided with a tightly focused laser pulse with a0 ~ 10. The interaction generated broadband synchrotron-like radiation from non-linear inverse Compton scattering (ICS) with critical energies > 30 MeV, which are the highest ICS photon energies reported from an all-optical setup at this time. The high photon energies in turn enabled a significant measurement of energy loss in the electron beam, rendering this the first published measurement of radiation reaction in an LWFA setup.

An electron beam from LWFA was used to commission a bremsstrahlung gamma-ray source reaching photon energies of several hundreds of MeV. Different materials and accelerator configurations were used to optimise the yield of photons and to mitigate the production of secondary particles.
The energetic gamma rays were then collided with the X-ray field emitted by a hot plasma in order to attempt the production of electron-positron pairs from the Breit-Wheeler process.