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

Abstract

The authors have investigated the two-step process 6²S_1/2 to 6²P_3/2 to (epsilon ²S_1/2, epsilon ²D_3/2, epsilon ²D_5/2) in Cs for circular polarization of the radiation in both steps. Theoretical expressions are presented for the photoelectron spin polarization P_z and the ion count-rate 'asymmetry' A_i (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 P_z and A_i, 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.