Transition frequencies of the D lines of ³⁹K, ⁴⁰K, and ⁴¹K measured with a femtosecond laser frequency comb

We report measurements of the transition frequencies 4s  ²S_1/2–4p  ²P_1/2 and 4s  ²S_1/2–4p  ²P_3/2 of the potassium isotopes 39, 40, and 41 through an atomic beam experiment with a fractional uncertainty of about 2×10^–10. For frequency calibration, a fs-laser comb referenced to a Cs atomic clock was used. Compared to previous results, hyperfine constants for the states 4p  ²P_1/2 and 4p  ²P_3/2 and isotope shifts are given with a considerably reduced uncertainty. This paper also resolves the discrepancy of transition frequencies measured by Banerjee et al. [Phys. Rev. A 70, 052505 (2004)] and Scherf et al. [Z. Phys. D 36, 31 (1996)] and the hyperfine constant A(³⁹K,²P_1/2) reported by Banerjee et al. [Europhys. Lett. 65, 172 (2004)] and Bendali et al. [J. Phys. B 14, 4231 (1981)].

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