Using XUV laser light to study the breakdown of perturbative strong-field QED*

Multi-petawatt laser facilities are currently running experiments colliding lasers with electron beams to study strong-field quantum electrodynamics (SFQED) processes, i.e., nonlinear Compton scattering and nonlinear Breit-Wheeler pair creation. In these experiements the quantum nonlinearity parameter will reach values χ∽10 where perturbative SFQED applies. It was conjectured by Ritus and Narozhny that under even more extreme conditions perturbative SFQED will break down and the scaling of the SFQED processes will change. Reaching this regime using optical laser light is well outside the capabilities of current multi-petawatt lasers; however, increasing the laser frequency greatly increases the possible χ and the probability of electrons reaching the maximum χ. Theory and simulation demonstrate that high-intensity XUV laser pulses will provide the χ necessary to study non-perturbative SFQED with measurable signatures in the gamma ray spectra. Sufficient laser frequencies and field strengths to begin studying this regime may be achieved through photon acceleration of a pulse in a plasma wakefield and subsequent focusing using a plasma lens.