Two-photon ionization of caesium via the 62P3/2intermediate state: analysis of photoelectron spin polarization and saturation effects

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Abstract
The authors have investigated the two-step process 62S1/2 to 62P3/2 to (epsilon 2S1/2, epsilon 2D3/2, epsilon 2D5/2) in Cs for circular polarization of the radiation in both steps. Theoretical expressions are presented for the photoelectron spin polarization Pz and the ion count-rate 'asymmetry' Ai (ratio of ion rates for right or left circular polarization in the second step), based on the hyperfine-coupling scheme for the first step. These expressions contain ratios of the three radial matrix elements involved in the ionizing step. The experimental determination of Pz and Ai, for different groups of hyperfine transitions, permits an evaluation of these ratios. The experiment was performed on a Cs atomic beam using a pulsed GaAs laser at 8521 AA for the first step and a pulsed Ar-ion laser at 5017-4545 AA for the second step. Effects of saturation in the first transition are studied and optimal conditions for use of the process in a spin-polarized electron source are discussed.