Two-electron atoms in short intense laser pulses

We discuss a method of solving the time-dependent Schr\"odinger equation for atoms with two active electrons in a strong laser field, which we used in a previous paper [A. Scrinzi and B. Piraux, Phys. Rev. A 56, R13 (1997)] to calculate ionization, double excitation, and harmonic generation in helium by short laser pulses. The method employs complex scaling and an expansion in an explicitly correlated basis. Convergence of the calculations is documented and error estimates are provided. The results for He at peak intensities up to 10¹⁵ W/cm² and wavelength 248 nm are accurate to at least 10%. Similarly accurate calculations are presented for electron detachment and double excitation of the negative hydrogen ion.