摘要
The two-photon transitions 4S <sub>1/2</sub> → 6S <sub>1/2</sub> and 4S <sub>1/2</sub> → 4D <sub>5/2</sub> in atomic potassium have been observed free of the first-order Doppler effect. The rate for the S-D transition, which has been detected for the first time, is two orders of magnitude lower than that for the S-S transition; the observed signal to noise ratios for the S-S and S-D transitions were respectively >200 and ~3. The laser excitation frequencies are located in the near vicinity of 1/6 of the 1S-2S transition interval of hydrogen, deuterium and the hydrogen-like atom, muonium. These potassium transitions may therefore provide a suitable frequency transfer standard for all these systems and a useful link between them.