Abstract
We consider the absorption of probe photons by electrons in the presence of an intense, pulsed, background field. Our analysis reveals an interplay between regularisation and gauge invariance which distinguishes absorption from its crossing-symmetric processes, as well as a physical interpretation of absorption in terms of degenerate processes in the weak field limit. In the strong field limit we develop a locally constant field approximation (LCFA) for absorption which also exhibits new features. We benchmark the LCFA against exact analytical calculations and explore its regime of validity. Pulse shape effects are also investigated, as well as infra-red and collinear limits of the absorption process.
Highlights
A number of upcoming experiments aim to probe quantum processes in intense laser fields, including pair production [1], vacuum birefringence [2], and conjectured regimes where all current perturbative approaches to QED break down [3,4,5,6]
The process appears simple at first sight, we will show that one can learn a lot about the regularization of strong-field processes and the applicability of the locally constant field approximation
II we provide some general results on the probability and cross section of scattering processes in strong fields, which we apply to the particular process of photon absorption by an electron in a laser pulse, in Sec
Summary
A number of upcoming experiments aim to probe quantum processes in intense laser fields, including pair production [1], vacuum birefringence [2], and conjectured regimes where all current perturbative approaches to QED break down [3,4,5,6]. A priority of the research field as a whole is the development of the right approximations and tools to more accurately model strongfield processes analytically and numerically. This requires a fresh look at previously neglected processes. A natural direction in which to extend existing efforts is to consider processes involving multiple incoming particles. Two such processes are pair-annihilation to one photon, and one-photon absorption by an electron.
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