Isotope shift and hyperfine structure measurements of 4s 2S1/2 → 6s 2S1/2 two-photon transition of potassium isotopes

Hyperfine splittings for the 39K and 41K isotopes and the isotope shift for the 4s 2S1/2 → 6s 2S1/2 two-photon transition have been measured using sub-Doppler fluorescence spectroscopy. We have accurately measured the transition isotope shift, and a discrepancy has been found in the earlier reported transition isotope shift value, which has been corrected. The resulting hyperfine splitting values of 418.2 (5) and 230.4 (1.3) MHz for the 39K and 41K isotopes respectively are in agreement with previous measurements. The precision of the absolute frequency values for the two-photon transition has been improved by about two orders. Our measured magnetic dipole constants for the upper 6 2S1/2 state for the 39K and the 41K isotopes are consistent with the earlier measured values.