Time-Dependent B-Spline R-Matrix Approach to Double Ionization of Atoms by XUV Laser Pulses

We have extended our {\it ab initio\/} and non-perturbative time-dependent approach to describe the effect of intense XUV laser pulses on a general atom~[1] to handle the double ionization process. After using a highly flexible $B$-Spline $R$-matrix method~[2] to generate field-free Hamiltonian and electric dipole matrices, the initial state is propagated in time using an efficient Arnoldi-Lanczos scheme. Test calculations for double ionization of He by a single laser pulse yield good agreement with benchmark results obtained with other methods, such as recent finite-element discrete-variable approaches~[3,4]. The method is then applied to two-color pump-probe processes, for which momentum and energy distributions of the two outgoing electrons are presented. [1]~X.~Guan {\it et al.}, Phys. Rev. A~{\bf 76}, 053411 (2006). [2]~O.~Zatsarinny, Comp. Phys. Commun. {\bf 174}, 273 (2006). [3]~J.~Feist {\it et al.}, Phys. Rev. A~{\bf 77}, 043420 (2007). [4]~X.~Guan {\it et al.}, Phys. Rev. A~{\bf 77}, 043421 (2007).