Ionization states for the multi-petawatt laser-QED regime

A paradigm shift in the physics of laser-plasma interactions is approaching with the commissioning of multi-petawatt laser facilities world-wide. Radiation reaction processes will result in the onset of electron-positron pair cascades and, with that, the absorption and partitioning of the incident laser energy, as well as the energy transport throughout the irradiated targets. To accurately quantify these effects, one must know the focused intensity on target in-situ. In this work, a new way of measuring the focused intensity on target is proposed based upon the ionization of Xe gas at low ambient pressure. The field ionization rates from Phys. Rev. A 59, 569 (1999) and from Phys. Rev. A 98, 043407 (2018), where the latter rate has been derived using quantum mechanics, have been implemented for the first time in the particle-in-cell code SMILEI [Comput. Phys. Commun. 222, 351-373 (2018)]. A series of one- and two-dimensional simulations are compared and shown to reproduce the charge states without presenting visible differences when increasing the simulation dimensionality. They provide a new way to accurately verify the intensity on target using in-situ measurements