Sequential ionization and energy gain of bound electrons in classical modeling of atoms in strong laser fields
Classical mechanics and classical ensembles have provided numerous insights into the dynamics of strong-field double ionization. In this paper, we show that in classical multidimensional modeling, the laser intensity at which sequential ionization begins to dominate depends on the softening of the interaction between the electron and nucleus. We show that an unsoftened interaction in two or three dimensions can lead to classical orbits in which an electron can start deep in the nuclear potential-energy well, gain energy from the oscillating laser field, and ionize over the barrier without any recollision. We discuss how this energy gain occurs, with the electron orbit favoring one side of the nucleus or the other, depending on which side corresponds with the rising potential-energy curve.