Precision Measurement of Hyperfine Constants and Isotope Shift of the Rb 6S State via a Two-Photon Transition

Using Doppler-free two-photon spectroscopy of the Rb 5S - 6S transition in a temperature-controlled vapor cell, for both naturally occurring isotopes, we have measured the hyperfine splittings and constants of the 6S state, and the isotope shift of the transition, to an accuracy of about 4 kHz. We locked a tunable microwave-driven EOM sideband of the 993 nm laser to an ultrastable very high finesse optical cavity, thus achieving microwave frequency accuracy for the relative laser tuning. The lineshapes are fit with a true Voigt profile. Our preliminary results are 717.200(4) and 1614.710(5) MHz for the hyperfine splittings, and 239.067(2) and 807.355(2) MHz for the hyperfine constants A, of the 85 and 87 Rb 6S state respectively, and -99.188(6) MHz for the isotope shift. These hyperfine constants are about 15 to 40 times more accurate than previously published results.