The interaction of charged particles and photons with intense electromagnetic fields gives rise to multi-photon Compton and Breit-Wheeler processes. The multi-photon nature of these processes implies the absorption of a significant number of photons. As a result, the interaction of a highly charged electron bunch with an intense laser pulse can lead to significant depletion of the laser pulse energy, thus rendering the external field approximation invalid.
The interaction of charged particles with ultra-intense electromagnetic (EM) pulses is the cornerstone of a newly emerging area of research, high intensity particle physics, located at the intersection of quantum electrodynamics (QED) and the theory of strong EM background fields. The latter significantly alter the physics of typical QED processes, leading to effects not encountered in perturbative quantum field theory. Recently, there has been a surge of interest in these processes due to the planning and realization of new laser facilities, which will be able to deliver EM pulses of unprecedented intensities to test the predictions of high intensity particle physics. Moreover, the development of compact multi-GeV laser electron accelerators adds another component necessary to carry out these studies. For large field amplitudes, a0>>1, the interaction of electrons/positrons and photons with strong EM fields involves the absorption of a large number of photons from the field.Clearly, these correspond to an energy loss of the laser background field, which may or may not be negligible. Revisiting the results on multi-photon Compton and Breit-Wheeler processes, we find that there is indeed a parameter range, for which depletion of the laser becomes substantial.
We acknowledge support from the Office of Science of the US DOE under Contract No. DE-AC02-05CH11231.