  We investigate multi-electron effects in strong-field ionization of Helium
using a semi-classical model that, unlike other commonly used theoretical
approaches, takes into account electron-electron correlation. Our approach has
an additional advantage of allowing to selectively switch off different
contributions from the parent ion (such as the remaining electron or the
nuclear charge) and thereby investigate in detail how the final electron angle
in the attoclock experiment is influenced by these contributions. We find that
the bound electron exerts a significant effect on the final electron momenta
distribution that can, however, be accounted for by an appropriately selected
mean field. Our results show excellent agreement with other widely used
theoretical models done within a single active electron approximation.

Atomic Physics