Generation of a 100-PW near-circularly-polarized attosecond x-ray pulse in the QED regime

An ultraintense, isolated circularly polarized (CP) attosecond x-ray pulse is often required for many application of pump-probe techniques. A quantum electrodynamics (QED) effect dominated coherent synchrotron emission (CSE) regime is proposed for the generation of an ultraintense isolated, nearly CP attosecond x-ray pulse. Due to the QED effects, the density of the target plasma increases due to Breit-Wheeler pair generation and the radiation reaction effects of gamma photons through the nonlinear Compton effect. As a result, the transparent target becomes an opaque target. Accordingly, the relativistic electron sheet (RES) can be accelerated toward a reflected direction only once. After that, the RES was pushed tempestuously forward continuously under the Lorentz force of the driving laser pulse. Therefore, an isolated, nearly CP attosecond x-ray pulse can be obtained in the reflected direction without filtering. The intensity of the nearly CP attosecond x-ray pulse can reach 2.48×10^{24}W/cm^{2} with ellipticity of 0.83, and the corresponding power can reach up to ∼100PW, which opens the door for nonlinear attosecond studies.