We constructed an optical Ramsey atomic interferometer, which has a resolution of 8 fm for the difference between arms of the interferometer, and used it to examine the phase shift due to the ac Stark effect of the excited state of the intercombination line ${(}^1$${\mathit{S}}_0$${\mathrm{-}}^3$${\mathit{P}}_1$) of Ca. It was clearly observed that the phase shift is in proportion to the field power and in inverse proportion to the detuning frequency of the laser. The proportionality coefficient obtained was in good agreement with the theoretical one.

• Received 8 April 1993

DOI:https://doi.org/10.1103/PhysRevA.48.1364