Single photoionization of highly charged atomic ions including the full electromagnetic-field potential

A previous fully relativistic time-dependent close-coupling method [Phys. Rev. A 81, 063431 (2010)], developed to study the photoionization of highly charged atomic ions, is substantially modified to include the full electromagnetic-field potential. Expansion of a one active electron wave function for the time-dependent Dirac equation in spin-orbit eigenfunctions yields close-coupled equations for bispinor radial wave functions. A spherical Bessel function expansion is then used to go beyond the Lorentz gauge dipole approximation to include higher order radiation field operators in both the Lorentz and Coulomb gauges. We test the high-order close-coupling method on the single photoionization of U91+.