Experimental Studies of Radiation Reaction and Photon-Photon Collisions in Ultrahigh Intensity Regimes

  • Guillermo Marrero Samarin

Student thesis: Doctoral ThesisDoctor of Philosophy


Quantum Electrodynamics (QED), in the perturbative limit has proved to be one of the most robust theoretical frameworks in physics, exhibiting vast calculation potential and being corroborated repeatedly by experimental observations. Nonetheless, there are still some open questions with regards to the theory in the non-perturbative limit, one of them being the problem of Radiation Reaction. Ongoing work in this field seeks to establish the exact relationship between the radiation emitted by a charged particle and its own motion.

An additional prospect of the advancement of the field of QED is the realisation of a photon-photon collider, one in which pairs of particles and anti-particles may be produced. While there are various mechanisms which entail the production of an electronpositron pair from photon-photon collisions, the most fundamental variant of the process has not been yet measured in isolation. This is the Breit-Wheeler process and it entails the collision of two real photons with a centre-of-mass energy above the rest mass of the particle-antiparticle pair.

The present document details an account of experimental works carried out in the aforementioned fields, with results being presented in both the subject of Radiation Reaction and Pair Production. The experiments were both carried out in all-optical scenarios, demonstrating the versatility and potential of the combination of laser-plasmaaccelerators and ultra-intense field capabilities in the same experimental facility.

The first of the experimental findings was the observation of non-perturbative Radiation Reaction effects in the collision of an electron beam of energy exceeding 2 GeV with an external electro-magnetic field of intensity of ≈ 1020 W/cm2 . This was the first successful execution of a laser-based radiation reaction experiment in a regime where the onset of quantum effects in electron dynamics was evident.

Furthermore, results from pair production from photon-photon collisions in the linear regime are also detailed. The experiment design, detector design and analysis methods are outlined and indications of the possible presence of positrons generated by the Breit-Wheeler process are presented with events beyond one standard deviation being observed. A statistical analysis was performed to ascertain the conditions necessary to observe events beyond two standard deviations in the same experimental conditions.
Date of AwardJul 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorGianluca Sarri (Supervisor) & Matthew Zepf (Supervisor)


  • Quantum Electrodynamics
  • Radiation Reaction
  • Photon Collisions
  • Pair Production
  • Statistical Methods

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