Nonlinear optical approach to matrix - element spectroscopy of the 5 s 2 S 1 / 2 → 5 p 2 P j → 5 d 2 D j ′ transitions in 87 Rb

We present in this paper results of a nonlinear optical spectroscopy approach to measurement of excited-state transition matrix elements. Recent advances in the quality of excited-state transition matrix elements have permitted renormalization of earlier measurements of transition amplitudes associated with the 5s S1/2 → 5p Pj → 5d D3/2 two-photon transitions in atomic 87Rb. Previous measurements were made to high precision, but further improvement of the accuracy was limited by uncertainties in data describing the influence of energetically distant transitions. Availability of more reliable matrix elements, including relativistic all-order calculations of transition matrix elements in alkali atoms, has since significantly improved the situation. In the present paper, we show that theoretical relative transition amplitudes for the excited state 5p Pj → 5d D3/2 doublet (ratio = 1.098(9)) are now in excellent agreement with experiment (ratio = 1.090(6)). This result, combined with our recent work on caesium, shows that it is possible to determine relative line strengths, for transitions connecting atomic excited states, with precision previously found only in state-of-the-art measurements of alkali resonance doublets. Detailed discussion of the experimental technique and supporting data, including polarization measurements on the 5s S1/2 → 5p Pj → 5d D5/2 transitions, is also presented. (Some figures in this article are in colour only in the electronic version) 0953-4075/06/112545+16$30.00 © 2006 IOP Publishing Ltd Printed in the UK 2545 2546 S B Bayram et al