The modeling non-sequential double ionization of helium under high-intensity femtosecond laser pulses with shielding charge approximation

In this study, we successfully extracted the "knee structure" for non-sequential double ionization (NSDI) in the helium atom. To achieve this, for the first time, we solved the time-dependent Schrödinger equation in three dimensions for the helium atom, utilizing the shielding charge approximation. Our findings corroborate prior observations by Wang et al. [Wang and Eberly, PRL 105, 083001 (2010)], demonstrating that NSDI occurs within a narrower time window in circular polarization compared to linear polarization. As a result, the yield of linear polarization was higher than that of circular polarization, aligning with the previously reported results. Notably, in the case of circular polarization, the time window further narrows with increasing intensity, attributed to a decrease in the time-of-flight.