Description
Nonlinear Compton scattering (NCS), the merging of multiple photons into one photon through collision with an electron, is a fundamental process in strong-field quantum electrodynamics (SFQED). Its degree of nonlinearity is quantified by the quantum nonlinearity parameter $\chi$, which is defined as the electromagnetic field strength observed by the electron in its rest frame relative to the intrinsic field strength in QED $E_S=1.3\times10^{18}~\mathrm{V/m}$.[1] In this regard, the condition $\chi=1$ can be considered a milestone for the transition from the weakly (perturbatively) nonlinear regime to the strongly (non-perturbatively) nonlinear regime; thus, the experimental realization of $\chi=1$ has been intensely pursued in the ultra-intense laser community. In this talk, we present recent experimental results obtained under the conditions $\chi=0.46$ [2] and $\chi=1.4$ at the Center for Relativistic Laser Science (CoReLS), reporting an entry into the strongly nonlinear regime. We also discuss the physical implications of these results, anticipating that nonlinear Breit-Wheeler pair production and QED cascades may be realized in the near future.
[1] V. I. Ritus, “Quantum effects of the interaction of elementary particles with an intense electromagnetic field,” Journal of Soviet Laser Research 6, 497 (1985).
[2] M. Mirzaie et al., “All-optical nonlinear Compton scattering performed with a multi-petawatt laser,” Nature Photonics 18, 1212 (2024).
