  Stimulated by a recent measurement of coherent control in photoionization of
atomic barium, we have calculated one- and two-photon ionization cross sections
of the aligned 6s6p^1P_1 state of barium in the energy range between the
5d_{3/2} and 5d_{5/2} states of Ba^+. We have also measured these
photionization spectra in the same energy region, driving the one- or
two-photon processes with the second or first harmonic of a tunable dye laser,
respectively. Our calculations employ the eigenchannel R-matrix method and
multichannel quantum defect theory to calculate the rich array of autoionizing
resonances in this energy range. The non-resonant two-photon process is
described using lowest-order perturbation theory for the photon-atom
interactions, with a discretized intermediate state one-electron continuum. The
calculations provide an absolute normalization for the experiment, and they
accurately reproduce the rich resonance structures in both the one and
two-photon cross sections, and confirm other aspects of experimental
observations. These results demonstrate the ability of these computationally
inexpensive methods to reproduce the experimental observables in one- and
two-photon ionization of heavy alkaline earths, and they lay the groundwork for
future studies of the phase-controlled interference between one-photon and
two-photon ionization processes.
