Abstract
Non-perturbative time-dependent calculations of single and double ionization of a one-dimensional model of atomic calcium by short and intense laser pulses were performed at various wavelengths. The comparison of the probabilities calculated within a two-active electron (TAE) approach with those obtained using a single-active electron (SAE) approximation clearly demonstrates the crucial role played by the electronic correlation and by doubly excited states within this model, even for the formation of Ca+.