Determination of ionic polarizability by nonsequential double ionization

We report on a theoretical study of nonsequential double ionization (NSDI) of magnesium atoms by circularly polarized intense laser pulses. We introduce a concise model considering the laser-induced dynamic core polarization, which is an often overlooked effect in understanding strong-field double ionization. By tracing back the electron trajectories, we demonstrate how the ionic response to the instantaneous laser field enhances the NSDI probability, which plays a crucial role in circular polarization. Furthermore, we propose a method to extract the ionic polarizability from the ratio of double to single ionization. This scheme can be applied to other polar targets and serves as a potential way to probe nonequilibrium states of strongly driven systems on the subfemtosecond timescale.