Measurement of the Rb(5D_5/2) photoionization cross section using trapped atoms

We report on measurements of the cross section for photoionization of Rb atoms in the highly excited 5D_5/2 level at wavelengths ranging from 1064 to 532 nm (photoelectron energies of 0.175 to 1.34 eV). We efficiently populate the 5D_5/2 level using coherent two-photon excitation of trapped atoms with pulses in the counterintuitive order. The absolute photoionization cross sections are then measured via the increased loss of atoms from the magneto-optical trap when it is illuminated by the photoionizing light. Our results are in good agreement with new calculations based on the valence-electron parametric potential method.