Precision measurement of hyperfine constants and isotope shift of the Rb 6S1/2 state via a two-photon transition

Using Doppler-free two-photon spectroscopy of the Rb 5S₁/₂ to 6S₁/₂ transition in a temperature-controlled vapor cell, for both naturally occurring isotopes, we measure to high accuracy the hyperfine splittings and constants, as well as the isotope shift of the 6S₁/₂ state. We lock a tunable microwave-driven electro-optic modulator sideband of the 993-nm laser to an ultrastable high-finesse cavity, thus achieving microwave frequency accuracy for the relative laser tuning. The line shapes are fit with a Voigt profile to extract line centers in order to calculate the hyperfine splittings, magnetic dipole hyperfine constants, isotope shift, and hyperfine anomaly. For the hyperfine splittings of the 6S₁/₂ state in ^85Rb and ^87Rb, respectively, we find 717. 195 (3) 0. 16em{0ex}MHz and 1614. 709 (3) 0. 16em{0ex}MHz. For the hyperfine constants A for the 6S₁/₂ states, we find 239. 065 (2) 0. 16em{0ex}MHz and 807. 355 (2) 0. 16em{0ex}MHz for ^85Rb and ^87Rb, respectively, and -99. 189 (3) 0. 16em{0ex}MHz for the isotope shift (^85Rb minus ^87Rb). These hyperfine splittings and constants are 10 to 25 times more accurate than previously published results. We measure the hyperfine anomaly ^85^87 of the 6S₁/₂ state to be -0. 00350 (1), which is about 20 times more accurate than previously published results.