Attosecond-scale absorption at extreme intensities*

The Zero Vector Potential (ZVP) absorption mechanism, a non-ponderomotive absorption mechanism, is expected to dominate the interactions of ultra-intense laser pulses with critically over-dense plasmas such as those that are expected with the Extreme Light Infrastructure laser systems. We extend the mechanism through the non-ponderomotive regime up to QED relevant intensities, showing that at the onset of electron-positron pair production in our numerical simulations the scaling relation of electron energy vs. laser intensity deviates significantly from that predicted by the ZVP model. This offers future experiments the opportunity to test for a distinctive signature in electron energy scalings with laser intensity, thereby providing the opportunity to validate the assumptions of current QED modules in particle-in-cell simulations.