Wavelength-dependent ac Stark shift of the ¹S₀‐³P₁ transition at 657 nm in Ca

We have measured the ac Stark shift of the 4s^2 1S₀–4s4p ³P₁ line in ⁴⁰Ca for perturbing laser wavelengths between 780 nm and 1064 nm with a time domain Ramsey-Bordé atom interferometer. We found a zero crossing of the shift for the m_S=0–m_P=0 transition and σ polarized perturbation at 800.8(22) nm. The data was analyzed by a model deriving the energy shift from known transition wavelengths and strengths. To fit our data, we adjusted the Einstein A coefficients of the 4s3d ³D–4s4p ³P and 4s5s ³S–4s4p ³P fine structure multiplets. With these we can predict vanishing ac Stark shifts for the ¹S₀ m=0–³P₁ m=1 transition and σ⁻ light at 983(12) nm and at 735.5(20) nm for the transition to the ³P₀ level.