Intensity ratios of ^2D_5/2,3/2 ← ^2S doublets in the two-photon absorption spectrum of Rb and Cs

Abstract
Absorption ratios of doublets arising from n2D5/2,3/2 ← n′2S transitions in Rb (n = 5–9, n′ = 5) and Cs (n = 7–13, n′ = 6) were measured by Doppler-free two-photon spectroscopy using a thermionic ion detector. The observed ratios agree with calculated values for transitions to the higher levels but differ significantly for levels n = 5 in Rb and n = 7, 8 in Cs. These experiments also provide new lower bounds for the ionization potentials of Rb2 (3.62 eV) and Cs2 (3.682 eV).