One-, two- and three-photon l-partial ionization cross sections from the ground state of the following helium-like atoms/ions: He, Li+, Ne8+ and Ar16+ are presented in this thesis. The expressions for the cross sections are based on the lowest-order perturbation theory for the electric eld while the calculations are made with the use of an ab-initio code using a conguration-interaction method. Two-electron eigenstates are expanded on the corresponding one-electron eigenstate basis which are expressed as a set of nonorthogonal B-spline polynomials in a nite interval. The dipole matrix elements, used to compute the cross-sections, are calculated in two gauges: length and velocity, and they generally have good relative agreement granting the results a degree of condence. It was found that cross sections are dominated by photo-resonance peaks as well as by peaks associated with two-electron excitation autoionizing resonances. It is observed that in the two-photon cross sections (in the non-resonant regions) the 1D channel overwhelms the 1S one. The general trend of decreasing cross sections with increasing atomic number (Z) of the target (i.e. from He to Ar16+) is observed.