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)0.16em0exMHz and 1614.709(3)0.16em0exMHz. For the hyperfine constants A for the 6S1/2 states, we find 239.065(2)0.16em0exMHz and 807.355(2)0.16em0exMHz for ⁸⁵Rb and ⁸⁷Rb, respectively, and -99.189(3)0.16em0exMHz 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 ⁸⁵Δ⁸⁷ of the 6S1/2 state to be -0.00350(1), which is about 20 times more accurate than previously published results.