A symmetrical atom interferometer with a thermal calcium atom beam has been developed using a narrow linewidth diode laser stabilized to the resonance of a high-finesse cavity. The linewidth of the diode laser was estimated to be less than 1 Hz relative to the cavity resonance in noise measurement over the range of 100 Hz to 1 MHz, and the phase instability of the interference fringes obtained from the Allan deviation was improved to 2 mrad at an integration time of 300 s. Using this atom interferometer, the ac Stark phase shift between the ${}^1$$S_0$ and ${}^3$$P_1$ states of a Ca atom was measured as a function of a laser power near the resonance of the ${}^1{S}_0{-}^1{P}_1$ transition at a wavelength of 423 nm. The decay rate of the ${}^1$$P_1$ state was determined to be $\gamma =1.91\left(33\right)\times {10}^8$ s${}^{-1}$.

• Received 27 May 2011

DOI:https://doi.org/10.1103/PhysRevA.84.023633