Multiphoton double ionization of the He atom

Time-dependent close-coupling (TDCC) calculations are made for the multiphoton double ionization of the He atom under the influence of a fast pulse XUV laser. One set of TDCC calculations employs $l_1 m_1 l_2 m_2$ coupling on a 2D ($r_1,r_2$) numerical lattice, a second set of TDCC calculations employs $m_1 m_2$ coupling on a 4D ($r_1, \theta_1, r_2, \theta_2$) numerical lattice, and a third set of TDCC calculations employs $m_1 m_2$ coupling on a 4D ($\rho_1, z_1, \rho_2, z_2$) numerical lattice. Studies are made to see which TDCC method is the most efficient at explaining measurements as the number of photons absorbed is increased.