Photoelectron Angular Distributions for Near-Threshold Two-Photon Ionization of Cesium and Rubidium Atoms

Photoelectron angular distributions have been measured for nonresonant two-photon ionization of cesium and rubidium atoms just above the ionization threshold. The photoelectron energies ranged from 25 to 100 meV. The results are compared with theoretical estimates based on nonrelativistic atomic wave functions. Initial results are also presented for above-threshold ionization in cesium.