Photoelectron angular distributions for cesium, rubidium, and sodium atoms using multiphoton ionization

Photoelectron angular distributions were investigated in cesium, rubidium, and sodium atoms using resonant and nonresonant multiphoton excitation techniques. The experiments were carried out by using a frequency-tunable dye laser as the excitation light source and a spherical sector electrostatic energy analyzer in conjunction with a dual channel plate detector. Photoelectron angular distribution measurements were performed for two-photon resonant, three photon ionization via the nd 2D states in cesium (n = 15-23), rubidium (n = 11-23), and sodium (n = 6-9) atoms. In all three cases, the j = 3/2 and j = 5/2 fine-structure levels of the nd 2D states were excited coherently, which could then couple with each other during the time that the laser pulse was on. The effect of this fine-structure coupling on the photoelectron angular distributions is reported. Photoelectron angular distributions were investigated for two-photon nonresonant ionization of cesium and rubidium atoms. These measurements were carried out as a function of the laser excitation wavelength in a region near the two-photon ionization threshold. Results of angular distributions for photoelectrons with kinetic energy in the range of approx. =25-100 MeV are reported