Hyperfine-structure investigation of highly excited ²D levels in ⁸⁷Rb and ¹³³Cs using a cw tunable dye laser in a two-step excitation scheme

The hyperfine structure of several highly excited ²D states in ⁸⁷Rb and ¹³³Cs has been measured. The D-state atoms were produced in a two-step-excitation process. In the first step, multiple scattering of the strong alkali-metal D₁ and D₂ lines from an rf lamp was used to excite atoms into the first excited ²P levels. The intense tunable radiation from a cw dye laser was used in the second step to transfer P-state atoms into highly excited D states. Level-crossing and optical-double-resonance techniques were used for the determination of the absolute values of the hyperfine-interaction constants. The following results (in MHz) were obtained for the magnetic dipole and the electric quadrupole interaction constants a and b: For ⁸⁷Rb, |a(6²D_3/2)|=7.84(5), |b(6²D_3/2)|=0.53(6) (b/a>0), |a(²D_5/2)|=3.6(7), |a(7²D_3/2)|=4.53(3), |b(7²D_3/2)|=0.26(4) (b/a>0), |a(7²D_5/2)|=2.2(5). For ¹³³Cs, |a(8²D_3/2)|=3.98(8), |a(8²D_5/2)|=0.9(4), |a(9²D_3/2)|=2.37(3), |a(9²D_5/2)|=0.5(2), |a(10²D_3/2)|=1.52(3), |a(10²D_5/2)|=0.4(2). The a factors generally deviate strongly from the values expected in a one-electron picture of the alkali-metal atom indicating the importance of polarization and correlation effects for these states. For ⁸⁷Rb a comparison with a recent calculation including polarization effects is made. The b factors for ⁸⁷Rb are the first significant values allowing a calculation of an alkali-metal-atom nuclear quadrupole moment from non-P-state data.